ssl — TLS/SSL wrapper for socket objects¶Source code: Lib/ssl.py
This module provides access to Transport Layer Security (often known as “Secure Sockets Layer”) encryption and peer authentication facilities for network sockets, both client-side and server-side. This module uses the OpenSSL library. It is available on all modern Unix systems, Windows, Mac OS X, and probably additional platforms, as long as OpenSSL is installed on that platform.
Note
Some behavior may be platform dependent, since calls are made to the operating system socket APIs. The installed version of OpenSSL may also cause variations in behavior. For example, TLSv1.1 and TLSv1.2 come with openssl version 1.0.1.
Warning
Don’t use this module without reading the Security considerations. Doing so may lead to a false sense of security, as the default settings of the ssl module are not necessarily appropriate for your application.
This section documents the objects and functions in the ssl module; for more
general information about TLS, SSL, and certificates, the reader is referred to
the documents in the “See Also” section at the bottom.
This module provides a class, ssl.SSLSocket, which is derived from the
socket.socket type, and provides a socket-like wrapper that also
encrypts and decrypts the data going over the socket with SSL. It supports
additional methods such as getpeercert(), which retrieves the
certificate of the other side of the connection, and cipher(),which
retrieves the cipher being used for the secure connection.
For more sophisticated applications, the ssl.SSLContext class
helps manage settings and certificates, which can then be inherited
by SSL sockets created through the SSLContext.wrap_socket() method.
Changed in version 3.6: OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported. In the future the ssl module will require at least OpenSSL 1.0.2 or 1.1.0.
ssl.SSLError¶Raised to signal an error from the underlying SSL implementation
(currently provided by the OpenSSL library). This signifies some
problem in the higher-level encryption and authentication layer that’s
superimposed on the underlying network connection. This error
is a subtype of OSError. The error code and message of
SSLError instances are provided by the OpenSSL library.
Changed in version 3.3: SSLError used to be a subtype of socket.error.
library¶A string mnemonic designating the OpenSSL submodule in which the error
occurred, such as SSL, PEM or X509. The range of possible
values depends on the OpenSSL version.
New in version 3.3.
reason¶A string mnemonic designating the reason this error occurred, for
example CERTIFICATE_VERIFY_FAILED. The range of possible
values depends on the OpenSSL version.
New in version 3.3.
ssl.SSLZeroReturnError¶A subclass of SSLError raised when trying to read or write and
the SSL connection has been closed cleanly. Note that this doesn’t
mean that the underlying transport (read TCP) has been closed.
New in version 3.3.
ssl.SSLWantReadError¶A subclass of SSLError raised by a non-blocking SSL socket when trying to read or write data, but more data needs
to be received on the underlying TCP transport before the request can be
fulfilled.
New in version 3.3.
ssl.SSLWantWriteError¶A subclass of SSLError raised by a non-blocking SSL socket when trying to read or write data, but more data needs
to be sent on the underlying TCP transport before the request can be
fulfilled.
New in version 3.3.
ssl.SSLSyscallError¶A subclass of SSLError raised when a system error was encountered
while trying to fulfill an operation on a SSL socket. Unfortunately,
there is no easy way to inspect the original errno number.
New in version 3.3.
ssl.SSLEOFError¶A subclass of SSLError raised when the SSL connection has been
terminated abruptly. Generally, you shouldn’t try to reuse the underlying
transport when this error is encountered.
New in version 3.3.
ssl.CertificateError¶Raised to signal an error with a certificate (such as mismatching
hostname). Certificate errors detected by OpenSSL, though, raise
an SSLError.
The following function allows for standalone socket creation. Starting from
Python 3.2, it can be more flexible to use SSLContext.wrap_socket()
instead.
ssl.wrap_socket(sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version={see docs}, ca_certs=None, do_handshake_on_connect=True, suppress_ragged_eofs=True, ciphers=None)¶Takes an instance sock of socket.socket, and returns an instance
of ssl.SSLSocket, a subtype of socket.socket, which wraps
the underlying socket in an SSL context. sock must be a
SOCK_STREAM socket; other socket types are unsupported.
For client-side sockets, the context construction is lazy; if the
underlying socket isn’t connected yet, the context construction will be
performed after connect() is called on the socket. For
server-side sockets, if the socket has no remote peer, it is assumed
to be a listening socket, and the server-side SSL wrapping is
automatically performed on client connections accepted via the
accept() method. wrap_socket() may raise SSLError.
The keyfile and certfile parameters specify optional files which
contain a certificate to be used to identify the local side of the
connection. See the discussion of Certificates for more
information on how the certificate is stored in the certfile.
The parameter server_side is a boolean which identifies whether
server-side or client-side behavior is desired from this socket.
The parameter cert_reqs specifies whether a certificate is required from
the other side of the connection, and whether it will be validated if
provided. It must be one of the three values CERT_NONE
(certificates ignored), CERT_OPTIONAL (not required, but validated
if provided), or CERT_REQUIRED (required and validated). If the
value of this parameter is not CERT_NONE, then the ca_certs
parameter must point to a file of CA certificates.
The ca_certs file contains a set of concatenated “certification
authority” certificates, which are used to validate certificates passed from
the other end of the connection. See the discussion of
Certificates for more information about how to arrange the
certificates in this file.
The parameter ssl_version specifies which version of the SSL protocol to
use. Typically, the server chooses a particular protocol version, and the
client must adapt to the server’s choice. Most of the versions are not
interoperable with the other versions. If not specified, the default is
PROTOCOL_TLS; it provides the most compatibility with other
versions.
Here’s a table showing which versions in a client (down the side) can connect to which versions in a server (along the top):
Footnotes
| [1] | (1, 2) SSLContext disables SSLv2 with OP_NO_SSLv2 by default. |
| [2] | (1, 2) SSLContext disables SSLv3 with OP_NO_SSLv3 by default. |
Note
Which connections succeed will vary depending on the version of OpenSSL. For example, before OpenSSL 1.0.0, an SSLv23 client would always attempt SSLv2 connections.
The ciphers parameter sets the available ciphers for this SSL object. It should be a string in the OpenSSL cipher list format.
The parameter do_handshake_on_connect specifies whether to do the SSL
handshake automatically after doing a socket.connect(), or whether the
application program will call it explicitly, by invoking the
SSLSocket.do_handshake() method. Calling
SSLSocket.do_handshake() explicitly gives the program control over the
blocking behavior of the socket I/O involved in the handshake.
The parameter suppress_ragged_eofs specifies how the
SSLSocket.recv() method should signal unexpected EOF from the other end
of the connection. If specified as True (the default), it returns a
normal EOF (an empty bytes object) in response to unexpected EOF errors
raised from the underlying socket; if False, it will raise the
exceptions back to the caller.
Changed in version 3.2: New optional argument ciphers.
A convenience function helps create SSLContext objects for common
purposes.
ssl.create_default_context(purpose=Purpose.SERVER_AUTH, cafile=None, capath=None, cadata=None)¶Return a new SSLContext object with default settings for
the given purpose. The settings are chosen by the ssl module,
and usually represent a higher security level than when calling the
SSLContext constructor directly.
cafile, capath, cadata represent optional CA certificates to
trust for certificate verification, as in
SSLContext.load_verify_locations(). If all three are
None, this function can choose to trust the system’s default
CA certificates instead.
The settings are: PROTOCOL_TLS, OP_NO_SSLv2, and
OP_NO_SSLv3 with high encryption cipher suites without RC4 and
without unauthenticated cipher suites. Passing SERVER_AUTH
as purpose sets verify_mode to CERT_REQUIRED
and either loads CA certificates (when at least one of cafile, capath or
cadata is given) or uses SSLContext.load_default_certs() to load
default CA certificates.
Note
The protocol, options, cipher and other settings may change to more restrictive values anytime without prior deprecation. The values represent a fair balance between compatibility and security.
If your application needs specific settings, you should create a
SSLContext and apply the settings yourself.
Note
If you find that when certain older clients or servers attempt to connect
with a SSLContext created by this function that they get an error
stating “Protocol or cipher suite mismatch”, it may be that they only
support SSL3.0 which this function excludes using the
OP_NO_SSLv3. SSL3.0 is widely considered to be completely broken. If you still wish to continue to
use this function but still allow SSL 3.0 connections you can re-enable
them using:
ctx = ssl.create_default_context(Purpose.CLIENT_AUTH)
ctx.options &= ~ssl.OP_NO_SSLv3
New in version 3.4.
Changed in version 3.4.4: RC4 was dropped from the default cipher string.
Changed in version 3.6: ChaCha20/Poly1305 was added to the default cipher string.
3DES was dropped from the default cipher string.
ssl.RAND_bytes(num)¶Return num cryptographically strong pseudo-random bytes. Raises an
SSLError if the PRNG has not been seeded with enough data or if the
operation is not supported by the current RAND method. RAND_status()
can be used to check the status of the PRNG and RAND_add() can be used
to seed the PRNG.
For almost all applications os.urandom() is preferable.
Read the Wikipedia article, Cryptographically secure pseudorandom number generator (CSPRNG), to get the requirements of a cryptographically generator.
New in version 3.3.
ssl.RAND_pseudo_bytes(num)¶Return (bytes, is_cryptographic): bytes are num pseudo-random bytes,
is_cryptographic is True if the bytes generated are cryptographically
strong. Raises an SSLError if the operation is not supported by the
current RAND method.
Generated pseudo-random byte sequences will be unique if they are of sufficient length, but are not necessarily unpredictable. They can be used for non-cryptographic purposes and for certain purposes in cryptographic protocols, but usually not for key generation etc.
For almost all applications os.urandom() is preferable.
New in version 3.3.
Deprecated since version 3.6: OpenSSL has deprecated ssl.RAND_pseudo_bytes(), use
ssl.RAND_bytes() instead.
ssl.RAND_status()¶Return True if the SSL pseudo-random number generator has been seeded
with ‘enough’ randomness, and False otherwise. You can use
ssl.RAND_egd() and ssl.RAND_add() to increase the randomness of
the pseudo-random number generator.
ssl.RAND_egd(path)¶If you are running an entropy-gathering daemon (EGD) somewhere, and path is the pathname of a socket connection open to it, this will read 256 bytes of randomness from the socket, and add it to the SSL pseudo-random number generator to increase the security of generated secret keys. This is typically only necessary on systems without better sources of randomness.
See http://egd.sourceforge.net/ or http://prngd.sourceforge.net/ for sources of entropy-gathering daemons.
Availability: not available with LibreSSL and OpenSSL > 1.1.0
ssl.RAND_add(bytes, entropy)¶Mix the given bytes into the SSL pseudo-random number generator. The
parameter entropy (a float) is a lower bound on the entropy contained in
string (so you can always use 0.0). See RFC 1750 for more
information on sources of entropy.
Changed in version 3.5: Writable bytes-like object is now accepted.
ssl.match_hostname(cert, hostname)¶Verify that cert (in decoded format as returned by
SSLSocket.getpeercert()) matches the given hostname. The rules
applied are those for checking the identity of HTTPS servers as outlined
in RFC 2818 and RFC 6125. In addition to HTTPS, this function
should be suitable for checking the identity of servers in various
SSL-based protocols such as FTPS, IMAPS, POPS and others.
CertificateError is raised on failure. On success, the function
returns nothing:
>>> cert = {'subject': ((('commonName', 'example.com'),),)}
>>> ssl.match_hostname(cert, "example.com")
>>> ssl.match_hostname(cert, "example.org")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/py3k/Lib/ssl.py", line 130, in match_hostname
ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'
New in version 3.2.
Changed in version 3.3.3: The function now follows RFC 6125, section 6.4.3 and does neither
match multiple wildcards (e.g. *.*.com or *a*.example.org) nor
a wildcard inside an internationalized domain names (IDN) fragment.
IDN A-labels such as www*.xn--pthon-kva.org are still supported,
but x*.python.org no longer matches xn--tda.python.org.
Changed in version 3.5: Matching of IP addresses, when present in the subjectAltName field of the certificate, is now supported.
ssl.cert_time_to_seconds(cert_time)¶Return the time in seconds since the Epoch, given the cert_time
string representing the “notBefore” or “notAfter” date from a
certificate in "%b %d %H:%M:%S %Y %Z" strptime format (C
locale).
Here’s an example:
>>> import ssl
>>> timestamp = ssl.cert_time_to_seconds("Jan 5 09:34:43 2018 GMT")
>>> timestamp
1515144883
>>> from datetime import datetime
>>> print(datetime.utcfromtimestamp(timestamp))
2018-01-05 09:34:43
“notBefore” or “notAfter” dates must use GMT (RFC 5280).
Changed in version 3.5: Interpret the input time as a time in UTC as specified by ‘GMT’ timezone in the input string. Local timezone was used previously. Return an integer (no fractions of a second in the input format)
ssl.get_server_certificate(addr, ssl_version=PROTOCOL_TLS, ca_certs=None)¶Given the address addr of an SSL-protected server, as a (hostname,
port-number) pair, fetches the server’s certificate, and returns it as a
PEM-encoded string. If ssl_version is specified, uses that version of
the SSL protocol to attempt to connect to the server. If ca_certs is
specified, it should be a file containing a list of root certificates, the
same format as used for the same parameter in wrap_socket(). The call
will attempt to validate the server certificate against that set of root
certificates, and will fail if the validation attempt fails.
Changed in version 3.3: This function is now IPv6-compatible.
Changed in version 3.5: The default ssl_version is changed from PROTOCOL_SSLv3 to
PROTOCOL_TLS for maximum compatibility with modern servers.
ssl.DER_cert_to_PEM_cert(DER_cert_bytes)¶Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded string version of the same certificate.
ssl.PEM_cert_to_DER_cert(PEM_cert_string)¶Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of bytes for that same certificate.
ssl.get_default_verify_paths()¶Returns a named tuple with paths to OpenSSL’s default cafile and capath.
The paths are the same as used by
SSLContext.set_default_verify_paths(). The return value is a
named tuple DefaultVerifyPaths:
cafile - resolved path to cafile or None if the file doesn’t exist,capath - resolved path to capath or None if the directory doesn’t exist,openssl_cafile_env - OpenSSL’s environment key that points to a cafile,openssl_cafile - hard coded path to a cafile,openssl_capath_env - OpenSSL’s environment key that points to a capath,openssl_capath - hard coded path to a capath directoryAvailability: LibreSSL ignores the environment vars
openssl_cafile_env and openssl_capath_env
New in version 3.4.
ssl.enum_certificates(store_name)¶Retrieve certificates from Windows’ system cert store. store_name may be
one of CA, ROOT or MY. Windows may provide additional cert
stores, too.
The function returns a list of (cert_bytes, encoding_type, trust) tuples.
The encoding_type specifies the encoding of cert_bytes. It is either
x509_asn for X.509 ASN.1 data or pkcs_7_asn for
PKCS#7 ASN.1 data. Trust specifies the purpose of the certificate as a set
of OIDS or exactly True if the certificate is trustworthy for all
purposes.
Example:
>>> ssl.enum_certificates("CA")
[(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),
(b'data...', 'x509_asn', True)]
Availability: Windows.
New in version 3.4.
ssl.enum_crls(store_name)¶Retrieve CRLs from Windows’ system cert store. store_name may be
one of CA, ROOT or MY. Windows may provide additional cert
stores, too.
The function returns a list of (cert_bytes, encoding_type, trust) tuples.
The encoding_type specifies the encoding of cert_bytes. It is either
x509_asn for X.509 ASN.1 data or pkcs_7_asn for
PKCS#7 ASN.1 data.
Availability: Windows.
New in version 3.4.
All constants are now
enum.IntEnumorenum.IntFlagcollections.New in version 3.6.
ssl.CERT_NONE¶Possible value for SSLContext.verify_mode, or the cert_reqs
parameter to wrap_socket(). In this mode (the default), no
certificates will be required from the other side of the socket connection.
If a certificate is received from the other end, no attempt to validate it
is made.
See the discussion of Security considerations below.
ssl.CERT_OPTIONAL¶Possible value for SSLContext.verify_mode, or the cert_reqs
parameter to wrap_socket(). In this mode no certificates will be
required from the other side of the socket connection; but if they
are provided, validation will be attempted and an SSLError
will be raised on failure.
Use of this setting requires a valid set of CA certificates to
be passed, either to SSLContext.load_verify_locations() or as a
value of the ca_certs parameter to wrap_socket().
ssl.CERT_REQUIRED¶Possible value for SSLContext.verify_mode, or the cert_reqs
parameter to wrap_socket(). In this mode, certificates are
required from the other side of the socket connection; an SSLError
will be raised if no certificate is provided, or if its validation fails.
Use of this setting requires a valid set of CA certificates to
be passed, either to SSLContext.load_verify_locations() or as a
value of the ca_certs parameter to wrap_socket().
ssl.VerifyMode¶enum.IntEnum collection of CERT_* constants.
New in version 3.6.
ssl.VERIFY_DEFAULT¶Possible value for SSLContext.verify_flags. In this mode, certificate
revocation lists (CRLs) are not checked. By default OpenSSL does neither
require nor verify CRLs.
New in version 3.4.
ssl.VERIFY_CRL_CHECK_LEAF¶Possible value for SSLContext.verify_flags. In this mode, only the
peer cert is check but non of the intermediate CA certificates. The mode
requires a valid CRL that is signed by the peer cert’s issuer (its direct
ancestor CA). If no proper has been loaded
SSLContext.load_verify_locations, validation will fail.
New in version 3.4.
ssl.VERIFY_CRL_CHECK_CHAIN¶Possible value for SSLContext.verify_flags. In this mode, CRLs of
all certificates in the peer cert chain are checked.
New in version 3.4.
ssl.VERIFY_X509_STRICT¶Possible value for SSLContext.verify_flags to disable workarounds
for broken X.509 certificates.
New in version 3.4.
ssl.VERIFY_X509_TRUSTED_FIRST¶Possible value for SSLContext.verify_flags. It instructs OpenSSL to
prefer trusted certificates when building the trust chain to validate a
certificate. This flag is enabled by default.
New in version 3.4.4.
ssl.VerifyFlags¶enum.IntFlag collection of VERIFY_* constants.
New in version 3.6.
ssl.PROTOCOL_TLS¶Selects the highest protocol version that both the client and server support. Despite the name, this option can select “TLS” protocols as well as “SSL”.
New in version 3.6.
ssl.PROTOCOL_TLS_CLIENT¶Auto-negotiate the highest protocol version like PROTOCOL_SSLv23,
but only support client-side SSLSocket connections. The protocol
enables CERT_REQUIRED and check_hostname by
default.
New in version 3.6.
ssl.PROTOCOL_TLS_SERVER¶Auto-negotiate the highest protocol version like PROTOCOL_SSLv23,
but only support server-side SSLSocket connections.
New in version 3.6.
ssl.PROTOCOL_SSLv23¶Alias for data:PROTOCOL_TLS.
Deprecated since version 3.6: Use PROTOCOL_TLS instead.
ssl.PROTOCOL_SSLv2¶Selects SSL version 2 as the channel encryption protocol.
This protocol is not available if OpenSSL is compiled with the
OPENSSL_NO_SSL2 flag.
Warning
SSL version 2 is insecure. Its use is highly discouraged.
Deprecated since version 3.6: OpenSSL has removed support for SSLv2.
ssl.PROTOCOL_SSLv3¶Selects SSL version 3 as the channel encryption protocol.
This protocol is not be available if OpenSSL is compiled with the
OPENSSL_NO_SSLv3 flag.
Warning
SSL version 3 is insecure. Its use is highly discouraged.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default
protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
ssl.PROTOCOL_TLSv1¶Selects TLS version 1.0 as the channel encryption protocol.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default
protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
ssl.PROTOCOL_TLSv1_1¶Selects TLS version 1.1 as the channel encryption protocol. Available only with openssl version 1.0.1+.
New in version 3.4.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default
protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
ssl.PROTOCOL_TLSv1_2¶Selects TLS version 1.2 as the channel encryption protocol. This is the most modern version, and probably the best choice for maximum protection, if both sides can speak it. Available only with openssl version 1.0.1+.
New in version 3.4.
Deprecated since version 3.6: OpenSSL has deprecated all version specific protocols. Use the default
protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.
ssl.OP_ALL¶Enables workarounds for various bugs present in other SSL implementations.
This option is set by default. It does not necessarily set the same
flags as OpenSSL’s SSL_OP_ALL constant.
New in version 3.2.
ssl.OP_NO_SSLv2¶Prevents an SSLv2 connection. This option is only applicable in
conjunction with PROTOCOL_TLS. It prevents the peers from
choosing SSLv2 as the protocol version.
New in version 3.2.
Deprecated since version 3.6: SSLv2 is deprecated
ssl.OP_NO_SSLv3¶Prevents an SSLv3 connection. This option is only applicable in
conjunction with PROTOCOL_TLS. It prevents the peers from
choosing SSLv3 as the protocol version.
New in version 3.2.
Deprecated since version 3.6: SSLv3 is deprecated
ssl.OP_NO_TLSv1¶Prevents a TLSv1 connection. This option is only applicable in
conjunction with PROTOCOL_TLS. It prevents the peers from
choosing TLSv1 as the protocol version.
New in version 3.2.
ssl.OP_NO_TLSv1_1¶Prevents a TLSv1.1 connection. This option is only applicable in conjunction
with PROTOCOL_TLS. It prevents the peers from choosing TLSv1.1 as
the protocol version. Available only with openssl version 1.0.1+.
New in version 3.4.
ssl.OP_NO_TLSv1_2¶Prevents a TLSv1.2 connection. This option is only applicable in conjunction
with PROTOCOL_TLS. It prevents the peers from choosing TLSv1.2 as
the protocol version. Available only with openssl version 1.0.1+.
New in version 3.4.
ssl.OP_CIPHER_SERVER_PREFERENCE¶Use the server’s cipher ordering preference, rather than the client’s. This option has no effect on client sockets and SSLv2 server sockets.
New in version 3.3.
ssl.OP_SINGLE_DH_USE¶Prevents re-use of the same DH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
New in version 3.3.
ssl.OP_SINGLE_ECDH_USE¶Prevents re-use of the same ECDH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
New in version 3.3.
ssl.OP_NO_COMPRESSION¶Disable compression on the SSL channel. This is useful if the application protocol supports its own compression scheme.
This option is only available with OpenSSL 1.0.0 and later.
New in version 3.3.
ssl.Options¶enum.IntFlag collection of OP_* constants.
ssl.OP_NO_TICKET¶Prevent client side from requesting a session ticket.
New in version 3.6.
ssl.HAS_ALPN¶Whether the OpenSSL library has built-in support for the Application-Layer Protocol Negotiation TLS extension as described in RFC 7301.
New in version 3.5.
ssl.HAS_ECDH¶Whether the OpenSSL library has built-in support for Elliptic Curve-based Diffie-Hellman key exchange. This should be true unless the feature was explicitly disabled by the distributor.
New in version 3.3.
ssl.HAS_SNI¶Whether the OpenSSL library has built-in support for the Server Name Indication extension (as defined in RFC 4366).
New in version 3.2.
ssl.HAS_NPN¶Whether the OpenSSL library has built-in support for Next Protocol
Negotiation as described in the NPN draft specification. When true,
you can use the SSLContext.set_npn_protocols() method to advertise
which protocols you want to support.
New in version 3.3.
ssl.CHANNEL_BINDING_TYPES¶List of supported TLS channel binding types. Strings in this list
can be used as arguments to SSLSocket.get_channel_binding().
New in version 3.3.
ssl.OPENSSL_VERSION¶The version string of the OpenSSL library loaded by the interpreter:
>>> ssl.OPENSSL_VERSION
'OpenSSL 1.0.2k 26 Jan 2017'
New in version 3.2.
ssl.OPENSSL_VERSION_INFO¶A tuple of five integers representing version information about the OpenSSL library:
>>> ssl.OPENSSL_VERSION_INFO
(1, 0, 2, 11, 15)
New in version 3.2.
ssl.OPENSSL_VERSION_NUMBER¶The raw version number of the OpenSSL library, as a single integer:
>>> ssl.OPENSSL_VERSION_NUMBER
268443839
>>> hex(ssl.OPENSSL_VERSION_NUMBER)
'0x100020bf'
New in version 3.2.
ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE¶ssl.ALERT_DESCRIPTION_INTERNAL_ERROR¶ALERT_DESCRIPTION_*Alert Descriptions from RFC 5246 and others. The IANA TLS Alert Registry contains this list and references to the RFCs where their meaning is defined.
Used as the return value of the callback function in
SSLContext.set_servername_callback().
New in version 3.4.
ssl.AlertDescription¶enum.IntEnum collection of ALERT_DESCRIPTION_* constants.
New in version 3.6.
Purpose.SERVER_AUTH¶Option for create_default_context() and
SSLContext.load_default_certs(). This value indicates that the
context may be used to authenticate Web servers (therefore, it will
be used to create client-side sockets).
New in version 3.4.
Purpose.CLIENT_AUTH¶Option for create_default_context() and
SSLContext.load_default_certs(). This value indicates that the
context may be used to authenticate Web clients (therefore, it will
be used to create server-side sockets).
New in version 3.4.
ssl.SSLErrorNumber¶enum.IntEnum collection of SSL_ERROR_* constants.
New in version 3.6.
ssl.SSLSocket(socket.socket)¶SSL sockets provide the following methods of Socket Objects:
accept()bind()close()connect()detach()fileno()getpeername(), getsockname()getsockopt(), setsockopt()gettimeout(), settimeout(),
setblocking()listen()makefile()recv(), recv_into()
(but passing a non-zero flags argument is not allowed)send(), sendall() (with
the same limitation)sendfile() (but os.sendfile will be used
for plain-text sockets only, else send() will be used)shutdown()However, since the SSL (and TLS) protocol has its own framing atop of TCP, the SSL sockets abstraction can, in certain respects, diverge from the specification of normal, OS-level sockets. See especially the notes on non-blocking sockets.
Usually, SSLSocket are not created directly, but using the
SSLContext.wrap_socket() method.
Changed in version 3.5: The sendfile() method was added.
Changed in version 3.5: The shutdown() does not reset the socket timeout each time bytes
are received or sent. The socket timeout is now to maximum total duration
of the shutdown.
Deprecated since version 3.6: It is deprecated to create a SSLSocket instance directly, use
SSLContext.wrap_socket() to wrap a socket.
SSL sockets also have the following additional methods and attributes:
SSLSocket.read(len=1024, buffer=None)¶Read up to len bytes of data from the SSL socket and return the result as
a bytes instance. If buffer is specified, then read into the buffer
instead, and return the number of bytes read.
Raise SSLWantReadError or SSLWantWriteError if the socket is
non-blocking and the read would block.
As at any time a re-negotiation is possible, a call to read() can also
cause write operations.
Changed in version 3.5: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to read up to len bytes.
Deprecated since version 3.6: Use recv() instead of read().
SSLSocket.write(buf)¶Write buf to the SSL socket and return the number of bytes written. The buf argument must be an object supporting the buffer interface.
Raise SSLWantReadError or SSLWantWriteError if the socket is
non-blocking and the write would block.
As at any time a re-negotiation is possible, a call to write() can
also cause read operations.
Changed in version 3.5: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to write buf.
Deprecated since version 3.6: Use send() instead of write().
Note
The read() and write() methods are the
low-level methods that read and write unencrypted, application-level data
and decrypt/encrypt it to encrypted, wire-level data. These methods
require an active SSL connection, i.e. the handshake was completed and
SSLSocket.unwrap() was not called.
Normally you should use the socket API methods like
recv() and send() instead of these
methods.
SSLSocket.do_handshake()¶Perform the SSL setup handshake.
Changed in version 3.4: The handshake method also performs match_hostname() when the
check_hostname attribute of the socket’s
context is true.
Changed in version 3.5: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration of the handshake.
SSLSocket.getpeercert(binary_form=False)¶If there is no certificate for the peer on the other end of the connection,
return None. If the SSL handshake hasn’t been done yet, raise
ValueError.
If the binary_form parameter is False, and a certificate was
received from the peer, this method returns a dict instance. If the
certificate was not validated, the dict is empty. If the certificate was
validated, it returns a dict with several keys, amongst them subject
(the principal for which the certificate was issued) and issuer
(the principal issuing the certificate). If a certificate contains an
instance of the Subject Alternative Name extension (see RFC 3280),
there will also be a subjectAltName key in the dictionary.
The subject and issuer fields are tuples containing the sequence
of relative distinguished names (RDNs) given in the certificate’s data
structure for the respective fields, and each RDN is a sequence of
name-value pairs. Here is a real-world example:
{'issuer': ((('countryName', 'IL'),),
(('organizationName', 'StartCom Ltd.'),),
(('organizationalUnitName',
'Secure Digital Certificate Signing'),),
(('commonName',
'StartCom Class 2 Primary Intermediate Server CA'),)),
'notAfter': 'Nov 22 08:15:19 2013 GMT',
'notBefore': 'Nov 21 03:09:52 2011 GMT',
'serialNumber': '95F0',
'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),),
(('countryName', 'US'),),
(('stateOrProvinceName', 'California'),),
(('localityName', 'San Francisco'),),
(('organizationName', 'Electronic Frontier Foundation, Inc.'),),
(('commonName', '*.eff.org'),),
(('emailAddress', 'hostmaster@eff.org'),)),
'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')),
'version': 3}
Note
To validate a certificate for a particular service, you can use the
match_hostname() function.
If the binary_form parameter is True, and a certificate was
provided, this method returns the DER-encoded form of the entire certificate
as a sequence of bytes, or None if the peer did not provide a
certificate. Whether the peer provides a certificate depends on the SSL
socket’s role:
getpeercert() will return
None if you used CERT_NONE (rather than
CERT_OPTIONAL or CERT_REQUIRED).Changed in version 3.2: The returned dictionary includes additional items such as issuer
and notBefore.
Changed in version 3.4: ValueError is raised when the handshake isn’t done.
The returned dictionary includes additional X509v3 extension items
such as crlDistributionPoints, caIssuers and OCSP URIs.
SSLSocket.cipher()¶Returns a three-value tuple containing the name of the cipher being used, the
version of the SSL protocol that defines its use, and the number of secret
bits being used. If no connection has been established, returns None.
Return the list of ciphers shared by the client during the handshake. Each
entry of the returned list is a three-value tuple containing the name of the
cipher, the version of the SSL protocol that defines its use, and the number
of secret bits the cipher uses. shared_ciphers() returns
None if no connection has been established or the socket is a client
socket.
New in version 3.5.
SSLSocket.compression()¶Return the compression algorithm being used as a string, or None
if the connection isn’t compressed.
If the higher-level protocol supports its own compression mechanism,
you can use OP_NO_COMPRESSION to disable SSL-level compression.
New in version 3.3.
SSLSocket.get_channel_binding(cb_type="tls-unique")¶Get channel binding data for current connection, as a bytes object. Returns
None if not connected or the handshake has not been completed.
The cb_type parameter allow selection of the desired channel binding
type. Valid channel binding types are listed in the
CHANNEL_BINDING_TYPES list. Currently only the ‘tls-unique’ channel
binding, defined by RFC 5929, is supported. ValueError will be
raised if an unsupported channel binding type is requested.
New in version 3.3.
SSLSocket.selected_alpn_protocol()¶Return the protocol that was selected during the TLS handshake. If
SSLContext.set_alpn_protocols() was not called, if the other party does
not support ALPN, if this socket does not support any of the client’s
proposed protocols, or if the handshake has not happened yet, None is
returned.
New in version 3.5.
SSLSocket.selected_npn_protocol()¶Return the higher-level protocol that was selected during the TLS/SSL
handshake. If SSLContext.set_npn_protocols() was not called, or
if the other party does not support NPN, or if the handshake has not yet
happened, this will return None.
New in version 3.3.
SSLSocket.unwrap()¶Performs the SSL shutdown handshake, which removes the TLS layer from the underlying socket, and returns the underlying socket object. This can be used to go from encrypted operation over a connection to unencrypted. The returned socket should always be used for further communication with the other side of the connection, rather than the original socket.
SSLSocket.version()¶Return the actual SSL protocol version negotiated by the connection
as a string, or None is no secure connection is established.
As of this writing, possible return values include "SSLv2",
"SSLv3", "TLSv1", "TLSv1.1" and "TLSv1.2".
Recent OpenSSL versions may define more return values.
New in version 3.5.
SSLSocket.pending()¶Returns the number of already decrypted bytes available for read, pending on the connection.
SSLSocket.context¶The SSLContext object this SSL socket is tied to. If the SSL
socket was created using the top-level wrap_socket() function
(rather than SSLContext.wrap_socket()), this is a custom context
object created for this SSL socket.
New in version 3.2.
SSLSocket.server_side¶A boolean which is True for server-side sockets and False for
client-side sockets.
New in version 3.2.
SSLSocket.server_hostname¶Hostname of the server: str type, or None for server-side
socket or if the hostname was not specified in the constructor.
New in version 3.2.
SSLSocket.session¶The SSLSession for this SSL connection. The session is available
for client and server side sockets after the TLS handshake has been
performed. For client sockets the session can be set before
do_handshake() has been called to reuse a session.
New in version 3.6.
SSLSocket.session_reused¶New in version 3.6.
New in version 3.2.
An SSL context holds various data longer-lived than single SSL connections, such as SSL configuration options, certificate(s) and private key(s). It also manages a cache of SSL sessions for server-side sockets, in order to speed up repeated connections from the same clients.
ssl.SSLContext(protocol=PROTOCOL_TLS)¶Create a new SSL context. You may pass protocol which must be one
of the PROTOCOL_* constants defined in this module.
PROTOCOL_TLS is currently recommended for maximum
interoperability and default value.
See also
create_default_context() lets the ssl module choose
security settings for a given purpose.
Changed in version 3.6: The context is created with secure default values. The options
OP_NO_COMPRESSION, OP_CIPHER_SERVER_PREFERENCE,
OP_SINGLE_DH_USE, OP_SINGLE_ECDH_USE,
OP_NO_SSLv2 (except for PROTOCOL_SSLv2),
and OP_NO_SSLv3 (except for PROTOCOL_SSLv3) are
set by default. The initial cipher suite list contains only HIGH
ciphers, no NULL ciphers and no MD5 ciphers (except for
PROTOCOL_SSLv2).
SSLContext objects have the following methods and attributes:
SSLContext.cert_store_stats()¶Get statistics about quantities of loaded X.509 certificates, count of X.509 certificates flagged as CA certificates and certificate revocation lists as dictionary.
Example for a context with one CA cert and one other cert:
>>> context.cert_store_stats()
{'crl': 0, 'x509_ca': 1, 'x509': 2}
New in version 3.4.
SSLContext.load_cert_chain(certfile, keyfile=None, password=None)¶Load a private key and the corresponding certificate. The certfile string must be the path to a single file in PEM format containing the certificate as well as any number of CA certificates needed to establish the certificate’s authenticity. The keyfile string, if present, must point to a file containing the private key in. Otherwise the private key will be taken from certfile as well. See the discussion of Certificates for more information on how the certificate is stored in the certfile.
The password argument may be a function to call to get the password for decrypting the private key. It will only be called if the private key is encrypted and a password is necessary. It will be called with no arguments, and it should return a string, bytes, or bytearray. If the return value is a string it will be encoded as UTF-8 before using it to decrypt the key. Alternatively a string, bytes, or bytearray value may be supplied directly as the password argument. It will be ignored if the private key is not encrypted and no password is needed.
If the password argument is not specified and a password is required, OpenSSL’s built-in password prompting mechanism will be used to interactively prompt the user for a password.
An SSLError is raised if the private key doesn’t
match with the certificate.
Changed in version 3.3: New optional argument password.
SSLContext.load_default_certs(purpose=Purpose.SERVER_AUTH)¶Load a set of default “certification authority” (CA) certificates from
default locations. On Windows it loads CA certs from the CA and
ROOT system stores. On other systems it calls
SSLContext.set_default_verify_paths(). In the future the method may
load CA certificates from other locations, too.
The purpose flag specifies what kind of CA certificates are loaded. The
default settings Purpose.SERVER_AUTH loads certificates, that are
flagged and trusted for TLS web server authentication (client side
sockets). Purpose.CLIENT_AUTH loads CA certificates for client
certificate verification on the server side.
New in version 3.4.
SSLContext.load_verify_locations(cafile=None, capath=None, cadata=None)¶Load a set of “certification authority” (CA) certificates used to validate
other peers’ certificates when verify_mode is other than
CERT_NONE. At least one of cafile or capath must be specified.
This method can also load certification revocation lists (CRLs) in PEM or
DER format. In order to make use of CRLs, SSLContext.verify_flags
must be configured properly.
The cafile string, if present, is the path to a file of concatenated CA certificates in PEM format. See the discussion of Certificates for more information about how to arrange the certificates in this file.
The capath string, if present, is the path to a directory containing several CA certificates in PEM format, following an OpenSSL specific layout.
The cadata object, if present, is either an ASCII string of one or more PEM-encoded certificates or a bytes-like object of DER-encoded certificates. Like with capath extra lines around PEM-encoded certificates are ignored but at least one certificate must be present.
Changed in version 3.4: New optional argument cadata
SSLContext.get_ca_certs(binary_form=False)¶Get a list of loaded “certification authority” (CA) certificates. If the
binary_form parameter is False each list
entry is a dict like the output of SSLSocket.getpeercert(). Otherwise
the method returns a list of DER-encoded certificates. The returned list
does not contain certificates from capath unless a certificate was
requested and loaded by a SSL connection.
Note
Certificates in a capath directory aren’t loaded unless they have been used at least once.
New in version 3.4.
SSLContext.get_ciphers()¶Get a list of enabled ciphers. The list is in order of cipher priority.
See SSLContext.set_ciphers().
Example:
>>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
>>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA')
>>> ctx.get_ciphers() # OpenSSL 1.0.x
[{'alg_bits': 256,
'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(256) Mac=AEAD',
'id': 50380848,
'name': 'ECDHE-RSA-AES256-GCM-SHA384',
'protocol': 'TLSv1/SSLv3',
'strength_bits': 256},
{'alg_bits': 128,
'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(128) Mac=AEAD',
'id': 50380847,
'name': 'ECDHE-RSA-AES128-GCM-SHA256',
'protocol': 'TLSv1/SSLv3',
'strength_bits': 128}]
>>> ctx.get_ciphers() # OpenSSL 1.1+
[{'aead': True,
'alg_bits': 256,
'auth': 'auth-rsa',
'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(256) Mac=AEAD',
'digest': None,
'id': 50380848,
'kea': 'kx-ecdhe',
'name': 'ECDHE-RSA-AES256-GCM-SHA384',
'protocol': 'TLSv1.2',
'strength_bits': 256,
'symmetric': 'aes-256-gcm'},
{'aead': True,
'alg_bits': 128,
'auth': 'auth-rsa',
'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(128) Mac=AEAD',
'digest': None,
'id': 50380847,
'kea': 'kx-ecdhe',
'name': 'ECDHE-RSA-AES128-GCM-SHA256',
'protocol': 'TLSv1.2',
'strength_bits': 128,
'symmetric': 'aes-128-gcm'}]
Availability: OpenSSL 1.0.2+
New in version 3.6.
SSLContext.set_default_verify_paths()¶Load a set of default “certification authority” (CA) certificates from a filesystem path defined when building the OpenSSL library. Unfortunately, there’s no easy way to know whether this method succeeds: no error is returned if no certificates are to be found. When the OpenSSL library is provided as part of the operating system, though, it is likely to be configured properly.
SSLContext.set_ciphers(ciphers)¶Set the available ciphers for sockets created with this context.
It should be a string in the OpenSSL cipher list format.
If no cipher can be selected (because compile-time options or other
configuration forbids use of all the specified ciphers), an
SSLError will be raised.
Note
when connected, the SSLSocket.cipher() method of SSL sockets will
give the currently selected cipher.
SSLContext.set_alpn_protocols(protocols)¶Specify which protocols the socket should advertise during the SSL/TLS
handshake. It should be a list of ASCII strings, like ['http/1.1',
'spdy/2'], ordered by preference. The selection of a protocol will happen
during the handshake, and will play out according to RFC 7301. After a
successful handshake, the SSLSocket.selected_alpn_protocol() method will
return the agreed-upon protocol.
This method will raise NotImplementedError if HAS_ALPN is
False.
OpenSSL 1.1.0+ will abort the handshake and raise SSLError when
both sides support ALPN but cannot agree on a protocol.
New in version 3.5.
SSLContext.set_npn_protocols(protocols)¶Specify which protocols the socket should advertise during the SSL/TLS
handshake. It should be a list of strings, like ['http/1.1', 'spdy/2'],
ordered by preference. The selection of a protocol will happen during the
handshake, and will play out according to the NPN draft specification. After a
successful handshake, the SSLSocket.selected_npn_protocol() method will
return the agreed-upon protocol.
This method will raise NotImplementedError if HAS_NPN is
False.
New in version 3.3.
SSLContext.set_servername_callback(server_name_callback)¶Register a callback function that will be called after the TLS Client Hello handshake message has been received by the SSL/TLS server when the TLS client specifies a server name indication. The server name indication mechanism is specified in RFC 6066 section 3 - Server Name Indication.
Only one callback can be set per SSLContext. If server_name_callback
is None then the callback is disabled. Calling this function a
subsequent time will disable the previously registered callback.
The callback function, server_name_callback, will be called with three
arguments; the first being the ssl.SSLSocket, the second is a string
that represents the server name that the client is intending to communicate
(or None if the TLS Client Hello does not contain a server name)
and the third argument is the original SSLContext. The server name
argument is the IDNA decoded server name.
A typical use of this callback is to change the ssl.SSLSocket‘s
SSLSocket.context attribute to a new object of type
SSLContext representing a certificate chain that matches the server
name.
Due to the early negotiation phase of the TLS connection, only limited
methods and attributes are usable like
SSLSocket.selected_alpn_protocol() and SSLSocket.context.
SSLSocket.getpeercert(), SSLSocket.getpeercert(),
SSLSocket.cipher() and SSLSocket.compress() methods require that
the TLS connection has progressed beyond the TLS Client Hello and therefore
will not contain return meaningful values nor can they be called safely.
The server_name_callback function must return None to allow the
TLS negotiation to continue. If a TLS failure is required, a constant
ALERT_DESCRIPTION_* can be
returned. Other return values will result in a TLS fatal error with
ALERT_DESCRIPTION_INTERNAL_ERROR.
If there is an IDNA decoding error on the server name, the TLS connection
will terminate with an ALERT_DESCRIPTION_INTERNAL_ERROR fatal TLS
alert message to the client.
If an exception is raised from the server_name_callback function the TLS
connection will terminate with a fatal TLS alert message
ALERT_DESCRIPTION_HANDSHAKE_FAILURE.
This method will raise NotImplementedError if the OpenSSL library
had OPENSSL_NO_TLSEXT defined when it was built.
New in version 3.4.
SSLContext.load_dh_params(dhfile)¶Load the key generation parameters for Diffie-Helman (DH) key exchange. Using DH key exchange improves forward secrecy at the expense of computational resources (both on the server and on the client). The dhfile parameter should be the path to a file containing DH parameters in PEM format.
This setting doesn’t apply to client sockets. You can also use the
OP_SINGLE_DH_USE option to further improve security.
New in version 3.3.
SSLContext.set_ecdh_curve(curve_name)¶Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH) key
exchange. ECDH is significantly faster than regular DH while arguably
as secure. The curve_name parameter should be a string describing
a well-known elliptic curve, for example prime256v1 for a widely
supported curve.
This setting doesn’t apply to client sockets. You can also use the
OP_SINGLE_ECDH_USE option to further improve security.
This method is not available if HAS_ECDH is False.
New in version 3.3.
See also
SSLContext.wrap_socket(sock, server_side=False, do_handshake_on_connect=True, suppress_ragged_eofs=True, server_hostname=None, session=None)¶Wrap an existing Python socket sock and return an SSLSocket
object. sock must be a SOCK_STREAM socket; other socket
types are unsupported.
The returned SSL socket is tied to the context, its settings and
certificates. The parameters server_side, do_handshake_on_connect
and suppress_ragged_eofs have the same meaning as in the top-level
wrap_socket() function.
On client connections, the optional parameter server_hostname specifies
the hostname of the service which we are connecting to. This allows a
single server to host multiple SSL-based services with distinct certificates,
quite similarly to HTTP virtual hosts. Specifying server_hostname will
raise a ValueError if server_side is true.
session, see session.
Changed in version 3.5: Always allow a server_hostname to be passed, even if OpenSSL does not have SNI.
Changed in version 3.6: session argument was added.
SSLContext.wrap_bio(incoming, outgoing, server_side=False, server_hostname=None, session=None)¶Create a new SSLObject instance by wrapping the BIO objects
incoming and outgoing. The SSL routines will read input data from the
incoming BIO and write data to the outgoing BIO.
The server_side, server_hostname and session parameters have the
same meaning as in SSLContext.wrap_socket().
Changed in version 3.6: session argument was added.
SSLContext.session_stats()¶Get statistics about the SSL sessions created or managed by this context. A dictionary is returned which maps the names of each piece of information to their numeric values. For example, here is the total number of hits and misses in the session cache since the context was created:
>>> stats = context.session_stats()
>>> stats['hits'], stats['misses']
(0, 0)
SSLContext.check_hostname¶Whether to match the peer cert’s hostname with match_hostname() in
SSLSocket.do_handshake(). The context’s
verify_mode must be set to CERT_OPTIONAL or
CERT_REQUIRED, and you must pass server_hostname to
wrap_socket() in order to match the hostname.
Example:
import socket, ssl
context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
context.verify_mode = ssl.CERT_REQUIRED
context.check_hostname = True
context.load_default_certs()
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ssl_sock = context.wrap_socket(s, server_hostname='www.verisign.com')
ssl_sock.connect(('www.verisign.com', 443))
New in version 3.4.
Note
This features requires OpenSSL 0.9.8f or newer.
SSLContext.options¶An integer representing the set of SSL options enabled on this context.
The default value is OP_ALL, but you can specify other options
such as OP_NO_SSLv2 by ORing them together.
Note
With versions of OpenSSL older than 0.9.8m, it is only possible
to set options, not to clear them. Attempting to clear an option
(by resetting the corresponding bits) will raise a ValueError.
Changed in version 3.6: SSLContext.options returns Options flags:
>>> ssl.create_default_context().options
<Options.OP_ALL|OP_NO_SSLv3|OP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>
SSLContext.protocol¶The protocol version chosen when constructing the context. This attribute is read-only.
SSLContext.verify_flags¶The flags for certificate verification operations. You can set flags like
VERIFY_CRL_CHECK_LEAF by ORing them together. By default OpenSSL
does neither require nor verify certificate revocation lists (CRLs).
Available only with openssl version 0.9.8+.
New in version 3.4.
Changed in version 3.6: SSLContext.verify_flags returns VerifyFlags flags:
>>> ssl.create_default_context().verify_flags
<VerifyFlags.VERIFY_X509_TRUSTED_FIRST: 32768>
SSLContext.verify_mode¶Whether to try to verify other peers’ certificates and how to behave
if verification fails. This attribute must be one of
CERT_NONE, CERT_OPTIONAL or CERT_REQUIRED.
Changed in version 3.6: SSLContext.verify_mode returns VerifyMode enum:
>>> ssl.create_default_context().verify_mode
<VerifyMode.CERT_REQUIRED: 2>
Certificates in general are part of a public-key / private-key system. In this system, each principal, (which may be a machine, or a person, or an organization) is assigned a unique two-part encryption key. One part of the key is public, and is called the public key; the other part is kept secret, and is called the private key. The two parts are related, in that if you encrypt a message with one of the parts, you can decrypt it with the other part, and only with the other part.
A certificate contains information about two principals. It contains the name of a subject, and the subject’s public key. It also contains a statement by a second principal, the issuer, that the subject is who he claims to be, and that this is indeed the subject’s public key. The issuer’s statement is signed with the issuer’s private key, which only the issuer knows. However, anyone can verify the issuer’s statement by finding the issuer’s public key, decrypting the statement with it, and comparing it to the other information in the certificate. The certificate also contains information about the time period over which it is valid. This is expressed as two fields, called “notBefore” and “notAfter”.
In the Python use of certificates, a client or server can use a certificate to prove who they are. The other side of a network connection can also be required to produce a certificate, and that certificate can be validated to the satisfaction of the client or server that requires such validation. The connection attempt can be set to raise an exception if the validation fails. Validation is done automatically, by the underlying OpenSSL framework; the application need not concern itself with its mechanics. But the application does usually need to provide sets of certificates to allow this process to take place.
Python uses files to contain certificates. They should be formatted as “PEM” (see RFC 1422), which is a base-64 encoded form wrapped with a header line and a footer line:
-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----
The Python files which contain certificates can contain a sequence of certificates, sometimes called a certificate chain. This chain should start with the specific certificate for the principal who “is” the client or server, and then the certificate for the issuer of that certificate, and then the certificate for the issuer of that certificate, and so on up the chain till you get to a certificate which is self-signed, that is, a certificate which has the same subject and issuer, sometimes called a root certificate. The certificates should just be concatenated together in the certificate file. For example, suppose we had a three certificate chain, from our server certificate to the certificate of the certification authority that signed our server certificate, to the root certificate of the agency which issued the certification authority’s certificate:
-----BEGIN CERTIFICATE-----
... (certificate for your server)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the certificate for the CA)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the root certificate for the CA's issuer)...
-----END CERTIFICATE-----
If you are going to require validation of the other side of the connection’s
certificate, you need to provide a “CA certs” file, filled with the certificate
chains for each issuer you are willing to trust. Again, this file just contains
these chains concatenated together. For validation, Python will use the first
chain it finds in the file which matches. The platform’s certificates file can
be used by calling SSLContext.load_default_certs(), this is done
automatically with create_default_context().
Often the private key is stored in the same file as the certificate; in this
case, only the certfile parameter to SSLContext.load_cert_chain()
and wrap_socket() needs to be passed. If the private key is stored
with the certificate, it should come before the first certificate in
the certificate chain:
-----BEGIN RSA PRIVATE KEY-----
... (private key in base64 encoding) ...
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----
If you are going to create a server that provides SSL-encrypted connection services, you will need to acquire a certificate for that service. There are many ways of acquiring appropriate certificates, such as buying one from a certification authority. Another common practice is to generate a self-signed certificate. The simplest way to do this is with the OpenSSL package, using something like the following:
% openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout cert.pem
Generating a 1024 bit RSA private key
.......++++++
.............................++++++
writing new private key to 'cert.pem'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:MyState
Locality Name (eg, city) []:Some City
Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc.
Organizational Unit Name (eg, section) []:My Group
Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com
Email Address []:ops@myserver.mygroup.myorganization.com
%
The disadvantage of a self-signed certificate is that it is its own root certificate, and no one else will have it in their cache of known (and trusted) root certificates.
To test for the presence of SSL support in a Python installation, user code should use the following idiom:
try:
import ssl
except ImportError:
pass
else:
... # do something that requires SSL support
This example creates a SSL context with the recommended security settings for client sockets, including automatic certificate verification:
>>> context = ssl.create_default_context()
If you prefer to tune security settings yourself, you might create a context from scratch (but beware that you might not get the settings right):
>>> context = ssl.SSLContext(ssl.PROTOCOL_TLS)
>>> context.verify_mode = ssl.CERT_REQUIRED
>>> context.check_hostname = True
>>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")
(this snippet assumes your operating system places a bundle of all CA
certificates in /etc/ssl/certs/ca-bundle.crt; if not, you’ll get an
error and have to adjust the location)
When you use the context to connect to a server, CERT_REQUIRED
validates the server certificate: it ensures that the server certificate
was signed with one of the CA certificates, and checks the signature for
correctness:
>>> conn = context.wrap_socket(socket.socket(socket.AF_INET),
... server_hostname="www.python.org")
>>> conn.connect(("www.python.org", 443))
You may then fetch the certificate:
>>> cert = conn.getpeercert()
Visual inspection shows that the certificate does identify the desired service
(that is, the HTTPS host www.python.org):
>>> pprint.pprint(cert)
{'OCSP': ('http://ocsp.digicert.com',),
'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',),
'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl',
'http://crl4.digicert.com/sha2-ev-server-g1.crl'),
'issuer': ((('countryName', 'US'),),
(('organizationName', 'DigiCert Inc'),),
(('organizationalUnitName', 'www.digicert.com'),),
(('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)),
'notAfter': 'Sep 9 12:00:00 2016 GMT',
'notBefore': 'Sep 5 00:00:00 2014 GMT',
'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26',
'subject': ((('businessCategory', 'Private Organization'),),
(('1.3.6.1.4.1.311.60.2.1.3', 'US'),),
(('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),
(('serialNumber', '3359300'),),
(('streetAddress', '16 Allen Rd'),),
(('postalCode', '03894-4801'),),
(('countryName', 'US'),),
(('stateOrProvinceName', 'NH'),),
(('localityName', 'Wolfeboro,'),),
(('organizationName', 'Python Software Foundation'),),
(('commonName', 'www.python.org'),)),
'subjectAltName': (('DNS', 'www.python.org'),
('DNS', 'python.org'),
('DNS', 'pypi.python.org'),
('DNS', 'docs.python.org'),
('DNS', 'testpypi.python.org'),
('DNS', 'bugs.python.org'),
('DNS', 'wiki.python.org'),
('DNS', 'hg.python.org'),
('DNS', 'mail.python.org'),
('DNS', 'packaging.python.org'),
('DNS', 'pythonhosted.org'),
('DNS', 'www.pythonhosted.org'),
('DNS', 'test.pythonhosted.org'),
('DNS', 'us.pycon.org'),
('DNS', 'id.python.org')),
'version': 3}
Now the SSL channel is established and the certificate verified, you can proceed to talk with the server:
>>> conn.sendall(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n")
>>> pprint.pprint(conn.recv(1024).split(b"\r\n"))
[b'HTTP/1.1 200 OK',
b'Date: Sat, 18 Oct 2014 18:27:20 GMT',
b'Server: nginx',
b'Content-Type: text/html; charset=utf-8',
b'X-Frame-Options: SAMEORIGIN',
b'Content-Length: 45679',
b'Accept-Ranges: bytes',
b'Via: 1.1 varnish',
b'Age: 2188',
b'X-Served-By: cache-lcy1134-LCY',
b'X-Cache: HIT',
b'X-Cache-Hits: 11',
b'Vary: Cookie',
b'Strict-Transport-Security: max-age=63072000; includeSubDomains',
b'Connection: close',
b'',
b'']
See the discussion of Security considerations below.
For server operation, typically you’ll need to have a server certificate, and
private key, each in a file. You’ll first create a context holding the key
and the certificate, so that clients can check your authenticity. Then
you’ll open a socket, bind it to a port, call listen() on it, and start
waiting for clients to connect:
import socket, ssl
context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")
bindsocket = socket.socket()
bindsocket.bind(('myaddr.mydomain.com', 10023))
bindsocket.listen(5)
When a client connects, you’ll call accept() on the socket to get the
new socket from the other end, and use the context’s SSLContext.wrap_socket()
method to create a server-side SSL socket for the connection:
while True:
newsocket, fromaddr = bindsocket.accept()
connstream = context.wrap_socket(newsocket, server_side=True)
try:
deal_with_client(connstream)
finally:
connstream.shutdown(socket.SHUT_RDWR)
connstream.close()
Then you’ll read data from the connstream and do something with it till you
are finished with the client (or the client is finished with you):
def deal_with_client(connstream):
data = connstream.recv(1024)
# empty data means the client is finished with us
while data:
if not do_something(connstream, data):
# we'll assume do_something returns False
# when we're finished with client
break
data = connstream.recv(1024)
# finished with client
And go back to listening for new client connections (of course, a real server would probably handle each client connection in a separate thread, or put the sockets in non-blocking mode and use an event loop).
SSL sockets behave slightly different than regular sockets in non-blocking mode. When working with non-blocking sockets, there are thus several things you need to be aware of:
Most SSLSocket methods will raise either
SSLWantWriteError or SSLWantReadError instead of
BlockingIOError if an I/O operation would
block. SSLWantReadError will be raised if a read operation on
the underlying socket is necessary, and SSLWantWriteError for
a write operation on the underlying socket. Note that attempts to
write to an SSL socket may require reading from the underlying
socket first, and attempts to read from the SSL socket may require
a prior write to the underlying socket.
Changed in version 3.5: In earlier Python versions, the SSLSocket.send() method
returned zero instead of raising SSLWantWriteError or
SSLWantReadError.
Calling select() tells you that the OS-level socket can be
read from (or written to), but it does not imply that there is sufficient
data at the upper SSL layer. For example, only part of an SSL frame might
have arrived. Therefore, you must be ready to handle SSLSocket.recv()
and SSLSocket.send() failures, and retry after another call to
select().
Conversely, since the SSL layer has its own framing, a SSL socket may
still have data available for reading without select()
being aware of it. Therefore, you should first call
SSLSocket.recv() to drain any potentially available data, and then
only block on a select() call if still necessary.
(of course, similar provisions apply when using other primitives such as
poll(), or those in the selectors module)
The SSL handshake itself will be non-blocking: the
SSLSocket.do_handshake() method has to be retried until it returns
successfully. Here is a synopsis using select() to wait for
the socket’s readiness:
while True:
try:
sock.do_handshake()
break
except ssl.SSLWantReadError:
select.select([sock], [], [])
except ssl.SSLWantWriteError:
select.select([], [sock], [])
See also
The asyncio module supports non-blocking SSL sockets and provides a
higher level API. It polls for events using the selectors module and
handles SSLWantWriteError, SSLWantReadError and
BlockingIOError exceptions. It runs the SSL handshake asynchronously
as well.
New in version 3.5.
Ever since the SSL module was introduced in Python 2.6, the SSLSocket
class has provided two related but distinct areas of functionality:
The network IO API is identical to that provided by socket.socket,
from which SSLSocket also inherits. This allows an SSL socket to be
used as a drop-in replacement for a regular socket, making it very easy to add
SSL support to an existing application.
Combining SSL protocol handling and network IO usually works well, but there
are some cases where it doesn’t. An example is async IO frameworks that want to
use a different IO multiplexing model than the “select/poll on a file
descriptor” (readiness based) model that is assumed by socket.socket
and by the internal OpenSSL socket IO routines. This is mostly relevant for
platforms like Windows where this model is not efficient. For this purpose, a
reduced scope variant of SSLSocket called SSLObject is
provided.
ssl.SSLObject¶A reduced-scope variant of SSLSocket representing an SSL protocol
instance that does not contain any network IO methods. This class is
typically used by framework authors that want to implement asynchronous IO
for SSL through memory buffers.
This class implements an interface on top of a low-level SSL object as implemented by OpenSSL. This object captures the state of an SSL connection but does not provide any network IO itself. IO needs to be performed through separate “BIO” objects which are OpenSSL’s IO abstraction layer.
An SSLObject instance can be created using the
wrap_bio() method. This method will create the
SSLObject instance and bind it to a pair of BIOs. The incoming
BIO is used to pass data from Python to the SSL protocol instance, while the
outgoing BIO is used to pass data the other way around.
The following methods are available:
contextserver_sideserver_hostnamesessionsession_reusedread()write()getpeercert()selected_npn_protocol()cipher()shared_ciphers()compression()pending()do_handshake()unwrap()get_channel_binding()When compared to SSLSocket, this object lacks the following
features:
recv() and
send().do_handshake() to start the handshake.SSLEOFError exception.unwrap() call does not return anything,
unlike for an SSL socket where it returns the underlying socket.SSLContext.set_servername_callback() will get an SSLObject
instance instead of a SSLSocket instance as its first parameter.Some notes related to the use of SSLObject:
SSLObject is non-blocking.
This means that for example read() will raise an
SSLWantReadError if it needs more data than the incoming BIO has
available.wrap_bio() call like there is for
wrap_socket(). An SSLObject is always created
via an SSLContext.An SSLObject communicates with the outside world using memory buffers. The
class MemoryBIO provides a memory buffer that can be used for this
purpose. It wraps an OpenSSL memory BIO (Basic IO) object:
ssl.MemoryBIO¶A memory buffer that can be used to pass data between Python and an SSL protocol instance.
pending¶Return the number of bytes currently in the memory buffer.
eof¶A boolean indicating whether the memory BIO is current at the end-of-file position.
read(n=-1)¶Read up to n bytes from the memory buffer. If n is not specified or negative, all bytes are returned.
write(buf)¶Write the bytes from buf to the memory BIO. The buf argument must be an object supporting the buffer protocol.
The return value is the number of bytes written, which is always equal to the length of buf.
New in version 3.6.
For client use, if you don’t have any special requirements for your
security policy, it is highly recommended that you use the
create_default_context() function to create your SSL context.
It will load the system’s trusted CA certificates, enable certificate
validation and hostname checking, and try to choose reasonably secure
protocol and cipher settings.
For example, here is how you would use the smtplib.SMTP class to
create a trusted, secure connection to a SMTP server:
>>> import ssl, smtplib
>>> smtp = smtplib.SMTP("mail.python.org", port=587)
>>> context = ssl.create_default_context()
>>> smtp.starttls(context=context)
(220, b'2.0.0 Ready to start TLS')
If a client certificate is needed for the connection, it can be added with
SSLContext.load_cert_chain().
By contrast, if you create the SSL context by calling the SSLContext
constructor yourself, it will not have certificate validation nor hostname
checking enabled by default. If you do so, please read the paragraphs below
to achieve a good security level.
When calling the SSLContext constructor directly,
CERT_NONE is the default. Since it does not authenticate the other
peer, it can be insecure, especially in client mode where most of time you
would like to ensure the authenticity of the server you’re talking to.
Therefore, when in client mode, it is highly recommended to use
CERT_REQUIRED. However, it is in itself not sufficient; you also
have to check that the server certificate, which can be obtained by calling
SSLSocket.getpeercert(), matches the desired service. For many
protocols and applications, the service can be identified by the hostname;
in this case, the match_hostname() function can be used. This common
check is automatically performed when SSLContext.check_hostname is
enabled.
In server mode, if you want to authenticate your clients using the SSL layer
(rather than using a higher-level authentication mechanism), you’ll also have
to specify CERT_REQUIRED and similarly check the client certificate.
Note
In client mode,
CERT_OPTIONALandCERT_REQUIREDare equivalent unless anonymous ciphers are enabled (they are disabled by default).
SSL versions 2 and 3 are considered insecure and are therefore dangerous to
use. If you want maximum compatibility between clients and servers, it is
recommended to use PROTOCOL_TLS_CLIENT or
PROTOCOL_TLS_SERVER as the protocol version. SSLv2 and SSLv3 are
disabled by default.
>>> client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
>>> client_context.options |= ssl.OP_NO_TLSv1
>>> client_context.options |= ssl.OP_NO_TLSv1_1
The SSL context created above will only allow TLSv1.2 and later (if
supported by your system) connections to a server. PROTOCOL_TLS_CLIENT
implies certificate validation and hostname checks by default. You have to
load certificates into the context.
If you have advanced security requirements, fine-tuning of the ciphers
enabled when negotiating a SSL session is possible through the
SSLContext.set_ciphers() method. Starting from Python 3.2.3, the
ssl module disables certain weak ciphers by default, but you may want
to further restrict the cipher choice. Be sure to read OpenSSL’s documentation
about the cipher list format.
If you want to check which ciphers are enabled by a given cipher list, use
SSLContext.get_ciphers() or the openssl ciphers command on your
system.
If using this module as part of a multi-processed application (using,
for example the multiprocessing or concurrent.futures modules),
be aware that OpenSSL’s internal random number generator does not properly
handle forked processes. Applications must change the PRNG state of the
parent process if they use any SSL feature with os.fork(). Any
successful call of RAND_add(), RAND_bytes() or
RAND_pseudo_bytes() is sufficient.
See also
socket.socketsocket class