##
3.3 `SSL` -- An interface to the SSL-specific parts of OpenSSL

This module handles things specific to SSL. There are two objects defined: Context, Connection.

`SSLv2_METHOD`
`SSLv3_METHOD`
`SSLv23_METHOD`
`TLSv1_METHOD`
  These constants represent the different SSL methods to use when creating a context object.

`VERIFY_NONE`
`VERIFY_PEER`
`VERIFY_FAIL_IF_NO_PEER_CERT`
  These constants represent the verification mode used by the Context object's `set_verify` method.

`FILETYPE_PEM`
`FILETYPE_ASN1`
  File type constants used with the `use_certificate_file` and `use_privatekey_file` methods of Context objects.

`OP_SINGLE_DH_USE`
`OP_EPHEMERAL_RSA`
`OP_NO_SSLv2`
`OP_NO_SSLv3`
`OP_NO_TLSv1`
  Constants used with `set_options` of Context objects. `OP_SINGLE_DH_USE` means to always create a new key when using ephemeral Diffie-Hellman. `OP_EPHEMERAL_RSA` means to always use ephemeral RSA keys when doing RSA operations. `OP_NO_SSLv2`, `OP_NO_SSLv3` and `OP_NO_TLSv1` means to disable those specific protocols. This is interesting if you're using e.g. `SSLv23_METHOD` to get an SSLv2-compatible handshake, but don't want to use SSLv2.

`SSLEAY_VERSION`
`SSLEAY_CFLAGS`
`SSLEAY_BUILT_ON`
`SSLEAY_PLATFORM`
`SSLEAY_DIR`
  Constants used with `SSLeay_version` to specify what OpenSSL version information to retrieve. See the man page for the `SSLeay_version` C API for details.

`OPENSSL_VERSION_NUMBER`
  An integer giving the version number of the OpenSSL library used to build this version of pyOpenSSL. See the man page for the `SSLeay_version` C API for details.

`SSLeay_version`(type)
  Retrieve a string describing some aspect of the underlying OpenSSL version. The type passed in should be one of the `SSLEAY_*` constants defined in this module.

`ContextType`
  See `Context`.

class `Context`(method)
  A class representing SSL contexts. Contexts define the parameters of one or more SSL connections.

  method should be `SSLv2_METHOD`, `SSLv3_METHOD`, `SSLv23_METHOD` or `TLSv1_METHOD`.

`ConnectionType`
  See `Connection`.

class `Connection`(context, socket)
  A class representing SSL connections.

  context should be an instance of `Context` and socket should be a socket 3 object. socket may be None; in this case, the Connection is created with a memory BIO: see the `bio_read`, `bio_write`, and `bio_shutdown` methods.

exception `Error`
  This exception is used as a base class for the other SSL-related exceptions, but may also be raised directly.

  Whenever this exception is raised directly, it has a list of error messages from the OpenSSL error queue, where each item is a tuple `(lib, function, reason)`. Here lib, function and reason are all strings, describing where and what the problem is. See err(3) for more information.

exception `ZeroReturnError`
  This exception matches the error return code `SSL_ERROR_ZERO_RETURN`, and is raised when the SSL Connection has been closed. In SSL 3.0 and TLS 1.0, this only occurs if a closure alert has occurred in the protocol, i.e. the connection has been closed cleanly. Note that this does not necessarily mean that the transport layer (e.g. a socket) has been closed.

  It may seem a little strange that this is an exception, but it does match an `SSL_ERROR` code, and is very convenient.

exception `WantReadError`
  The operation did not complete; the same I/O method should be called again later, with the same arguments. Any I/O method can lead to this since new handshakes can occur at any time.

  The wanted read is for dirty data sent over the network, not the clean data inside the tunnel. For a socket based SSL connection, read means data coming at us over the network. Until that read succeeds, the attempted `OpenSSL.SSL.Connection.recv`, `OpenSSL.SSL.Connection.send`, or `OpenSSL.SSL.Connection.do_handshake` is prevented or incomplete. You probably want to `select()` on the socket before trying again.

exception `WantWriteError`
  See `WantReadError`. The socket send buffer may be too full to write more data.

exception `WantX509LookupError`
  The operation did not complete because an application callback has asked to be called again. The I/O method should be called again later, with the same arguments. Note: This won't occur in this version, as there are no such callbacks in this version.

exception `SysCallError`
  The `SysCallError` occurs when there's an I/O error and OpenSSL's error queue does not contain any information. This can mean two things: An error in the transport protocol, or an end of file that violates the protocol. The parameter to the exception is always a pair `(errnum, errstr)`.

#### Footnotes

... socket 3
  Actually, all that is required is an object that behaves like a socket, you could even use files, even though it'd be tricky to get the handshakes right!

Subsections

- 3.3.1 Context objects
- 3.3.2 Connection objects