ssl - OpenSSL SSL/TLS library
See the individual manual pages for details.
The OpenSSL ssl library implements several versions of the
Secure Sockets Layer, Transport Layer Security, and Datagram Transport Layer
Security protocols. This page gives a brief overview of the extensive API
and data types provided by the library.
An SSL_CTX object is created as a framework to establish
TLS/SSL enabled connections (see SSL_CTX_new(3)). Various options
regarding certificates, algorithms etc. can be set in this object.
When a network connection has been created, it can be assigned to
an SSL object. After the SSL object has been created using
SSL_new(3), SSL_set_fd(3) or SSL_set_bio(3) can be used
to associate the network connection with the object.
When the TLS/SSL handshake is performed using SSL_accept(3)
or SSL_connect(3) respectively. SSL_read_ex(3),
SSL_read(3), SSL_write_ex(3) and SSL_write(3) are used
to read and write data on the TLS/SSL connection. SSL_shutdown(3) can
be used to shut down the TLS/SSL connection.
Here are some of the main data structures in the library.
- SSL_METHOD
(SSL Method)
- This is a dispatch structure describing the internal ssl library
methods/functions which implement the various protocol versions (SSLv3
TLSv1, ...). It's needed to create an SSL_CTX.
- SSL_CIPHER
(SSL Cipher)
- This structure holds the algorithm information for a particular cipher
which are a core part of the SSL/TLS protocol. The available ciphers are
configured on a SSL_CTX basis and the actual ones used are then
part of the SSL_SESSION.
- SSL_CTX (SSL
Context)
- This is the global context structure which is created by a server or
client once per program life-time and which holds mainly default values
for the SSL structures which are later created for the
connections.
- SSL_SESSION
(SSL Session)
- This is a structure containing the current TLS/SSL session details for a
connection: SSL_CIPHERs, client and server certificates, keys,
etc.
- SSL (SSL
Connection)
- This is the main SSL/TLS structure which is created by a server or client
per established connection. This actually is the core structure in the SSL
API. At run-time the application usually deals with this structure which
has links to mostly all other structures.
Currently the OpenSSL ssl library provides the following C
header files containing the prototypes for the data structures and
functions:
- <openssl/ssl.h>
- This is the common header file for the SSL/TLS API. Include it into your
program to make the API of the ssl library available. It internally
includes both more private SSL headers and headers from the crypto
library. Whenever you need hard-core details on the internals of the SSL
API, look inside this header file. This file also includes the others
listed below.
- <openssl/ssl2.h>
- Unused. Present for backwards compatibility only.
- <openssl/ssl3.h>
- This is the sub header file dealing with the SSLv3 protocol only.
- <openssl/tls1.h>
- This is the sub header file dealing with the TLSv1 protocol only.
Copyright 2000-2018 The OpenSSL Project Authors. All Rights
Reserved.
Licensed under the Apache License 2.0 (the "License").
You may not use this file except in compliance with the License. You can
obtain a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.