The OpenSSL ssl library implements the Secure Sockets Layer (SSL v2/v3) and
Transport Layer Security (TLS v1) protocols. It provides a rich API which is
documented here.
At first the library must be initialized; see
SSL_library_init(3).
Then 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.
Then the TLS/SSL handshake is performed using
SSL_accept(3) or SSL_connect(3)
respectively.
SSL_read(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.
DATA STRUCTURES
Currently the OpenSSL ssl library functions deals with the following data
structures:
SSL_METHOD (SSL Method)
That's a dispatch structure describing the internal ssl library
methods/functions which implement the various protocol versions (SSLv1, SSLv2
and 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 actually used ones are then part of the
SSL_SESSION.
SSL_CTX (SSL Context)
That's 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)
That's 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.
Under run-time the application usually deals with this structure which has
links to mostly all other structures.
HEADER FILES
Currently the OpenSSL ssl library provides the following C header files
containing the prototypes for the data structures and and functions:
ssl.h
That's 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.
ssl2.h
That's the sub header file dealing with the SSLv2 protocol only.
Usually you don't have to include it explicitly because
it's already included by ssl.h.
ssl3.h
That's the sub header file dealing with the SSLv3 protocol only.
Usually you don't have to include it explicitly because
it's already included by ssl.h.
ssl23.h
That's the sub header file dealing with the combined use of the SSLv2 and
SSLv3 protocols.
Usually you don't have to include it explicitly because
it's already included by ssl.h.
tls1.h
That's the sub header file dealing with the TLSv1 protocol only.
Usually you don't have to include it explicitly because
it's already included by ssl.h.
API FUNCTIONS
Currently the OpenSSL ssl library exports 214 API functions.
They are documented in the following:
DEALING WITH PROTOCOL METHODS
Here we document the various API functions which deal with the SSL/TLS
protocol methods defined in SSL_METHOD structures.
SSL_METHOD *SSLv2_client_method(void);
Constructor for the SSLv2 SSL_METHOD structure for a dedicated client.
SSL_METHOD *SSLv2_server_method(void);
Constructor for the SSLv2 SSL_METHOD structure for a dedicated server.
SSL_METHOD *SSLv2_method(void);
Constructor for the SSLv2 SSL_METHOD structure for combined client and server.
SSL_METHOD *SSLv3_client_method(void);
Constructor for the SSLv3 SSL_METHOD structure for a dedicated client.
SSL_METHOD *SSLv3_server_method(void);
Constructor for the SSLv3 SSL_METHOD structure for a dedicated server.
SSL_METHOD *SSLv3_method(void);
Constructor for the SSLv3 SSL_METHOD structure for combined client and server.
SSL_METHOD *TLSv1_client_method(void);
Constructor for the TLSv1 SSL_METHOD structure for a dedicated client.
SSL_METHOD *TLSv1_server_method(void);
Constructor for the TLSv1 SSL_METHOD structure for a dedicated server.
SSL_METHOD *TLSv1_method(void);
Constructor for the TLSv1 SSL_METHOD structure for combined client and server.
DEALING WITH CIPHERS
Here we document the various API functions which deal with the SSL/TLS
ciphers defined in SSL_CIPHER structures.
char *SSL_CIPHER_description(SSL_CIPHER *cipher, char *buf, int len);
Write a string to buf (with a maximum size of len) containing a human
readable description of cipher. Returns buf.
int SSL_CIPHER_get_bits(SSL_CIPHER *cipher, int *alg_bits);
Determine the number of bits in cipher. Because of export crippled ciphers
there are two bits: The bits the algorithm supports in general (stored to
alg_bits) and the bits which are actually used (the return value).
Return the internal name of cipher as a string. These are the various
strings defined by the SSL2_TXT_xxx, SSL3_TXT_xxx and TLS1_TXT_xxx
definitions in the header files.
char *SSL_CIPHER_get_version(SSL_CIPHER *cipher);
Returns a string like ""TLSv1/SSLv3"`` or ''"SSLv2"" which indicates the
SSL/TLS protocol version to which cipher belongs (i.e. where it was defined
in the specification the first time).
DEALING WITH PROTOCOL CONTEXTS
Here we document the various API functions which deal with the SSL/TLS
protocol context defined in the SSL_CTX structure.
int SSL_CTX_add_client_CA(SSL_CTX *ctx, X509 *x);
long SSL_CTX_add_extra_chain_cert(SSL_CTX *ctx, X509 *x509);
int SSL_CTX_add_session(SSL_CTX *ctx, SSL_SESSION *c);
int SSL_CTX_check_private_key(const SSL_CTX *ctx);
long SSL_CTX_ctrl(SSL_CTX *ctx, int cmd, long larg, char *parg);
void SSL_CTX_set_options(SSL_CTX *ctx, unsigned long op);
void SSL_CTX_set_quiet_shutdown(SSL_CTX *ctx, int mode);
void SSL_CTX_set_session_cache_mode(SSL_CTX *ctx, int mode);
int SSL_CTX_set_ssl_version(SSL_CTX *ctx, SSL_METHOD *meth);
void SSL_CTX_set_timeout(SSL_CTX *ctx, long t);
long SSL_CTX_set_tmp_dh(SSL_CTX* ctx, DH *dh);
long SSL_CTX_set_tmp_dh_callback(SSL_CTX *ctx, DH *(*cb)(void));
long SSL_CTX_set_tmp_rsa(SSL_CTX *ctx, RSA *rsa);
SSL_CTX_set_tmp_rsa_callback
"long SSL_CTX_set_tmp_rsa_callback(SSL_CTX *ctx, RSA *(*cb)(SSL *ssl, int export, int keylength));"
Sets the callback which will be called when a temporary private key is
required. The "export" flag will be set if the reason for needing
a temp key is that an export ciphersuite is in use, in which case,
"keylength" will contain the required keylength in bits. Generate a key of
appropriate size (using ???) and return it.
SSL_set_tmp_rsa_callback
long SSL_set_tmp_rsa_callback(SSL *ssl, RSA *(*cb)(SSL *ssl, int export, int keylength));
The same as SSL_CTX_set_tmp_rsa_callback, except it operates on an SSL
session instead of a context.
void SSL_CTX_set_verify(SSL_CTX *ctx, int mode, int (*cb);(void))
int SSL_CTX_use_PrivateKey(SSL_CTX *ctx, EVP_PKEY *pkey);
int SSL_CTX_use_PrivateKey_ASN1(int type, SSL_CTX *ctx, unsigned char *d, long len);
int SSL_CTX_use_PrivateKey_file(SSL_CTX *ctx, char *file, int type);
int SSL_CTX_use_RSAPrivateKey(SSL_CTX *ctx, RSA *rsa);
int SSL_CTX_use_RSAPrivateKey_ASN1(SSL_CTX *ctx, unsigned char *d, long len);
int SSL_CTX_use_RSAPrivateKey_file(SSL_CTX *ctx, char *file, int type);
int SSL_CTX_use_certificate(SSL_CTX *ctx, X509 *x);
int SSL_CTX_use_certificate_ASN1(SSL_CTX *ctx, int len, unsigned char *d);
int SSL_CTX_use_certificate_file(SSL_CTX *ctx, char *file, int type);
DEALING WITH SESSIONS
Here we document the various API functions which deal with the SSL/TLS
sessions defined in the SSL_SESSION structures.
int SSL_SESSION_cmp(const SSL_SESSION *a, const SSL_SESSION *b);
void SSL_SESSION_free(SSL_SESSION *ss);
char *SSL_SESSION_get_app_data(SSL_SESSION *s);
char *SSL_SESSION_get_ex_data(const SSL_SESSION *s, int idx);
int SSL_SESSION_get_ex_new_index(long argl, char *argp, int (*new_func);(void), int (*dup_func)(void), void (*free_func)(void))
long SSL_SESSION_get_time(const SSL_SESSION *s);
long SSL_SESSION_get_timeout(const SSL_SESSION *s);
unsigned long SSL_SESSION_hash(const SSL_SESSION *a);
SSL_SESSION *SSL_SESSION_new(void);
int SSL_SESSION_print(BIO *bp, const SSL_SESSION *x);
int SSL_SESSION_print_fp(FILE *fp, const SSL_SESSION *x);