SSL - OpenSSL SSL/TLS library DESCRIPTIONThe 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 STRUCTURESCurrently 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 FILESCurrently 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 FUNCTIONSCurrently 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(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 B<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 C<export> flag will be set
if the reason for needing a temp key is that an export ciphersuite
is in use, in which case, C<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(SSL_SESSION *a,
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(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(SSL_SESSION *s);
long SSL_SESSION_get_timeout(SSL_SESSION *s);
unsigned long SSL_SESSION_hash(SSL_SESSION *a);
SSL_SESSION *SSL_SESSION_new(void);
int SSL_SESSION_print(BIO *bp, SSL_SESSION *x);
int SSL_SESSION_print_fp(FILE *fp, SSL_SESSION *x);