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ssl(3) OpenSSL ssl(3)
NAME
SSL - OpenSSL SSL/TLS library
SYNOPSIS
DESCRIPTION
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.
const SSL_METHOD *SSLv23_method(void);
Constructor for the version-flexible SSL_METHOD structure for
clients, servers or both. See SSL_CTX_new(3) for details.
const SSL_METHOD *SSLv23_client_method(void);
Constructor for the version-flexible SSL_METHOD structure for
clients.
const SSL_METHOD *SSLv23_client_method(void);
Constructor for the version-flexible SSL_METHOD structure for
servers.
const SSL_METHOD *TLSv1_2_method(void);
Constructor for the TLSv1.2 SSL_METHOD structure for clients,
servers or both.
const SSL_METHOD *TLSv1_2_client_method(void);
Constructor for the TLSv1.2 SSL_METHOD structure for clients.
const SSL_METHOD *TLSv1_2_server_method(void);
Constructor for the TLSv1.2 SSL_METHOD structure for servers.
const SSL_METHOD *TLSv1_1_method(void);
Constructor for the TLSv1.1 SSL_METHOD structure for clients,
servers or both.
const SSL_METHOD *TLSv1_1_client_method(void);
Constructor for the TLSv1.1 SSL_METHOD structure for clients.
const SSL_METHOD *TLSv1_1_server_method(void);
Constructor for the TLSv1.1 SSL_METHOD structure for servers.
const SSL_METHOD *TLSv1_method(void);
Constructor for the TLSv1 SSL_METHOD structure for clients, servers
or both.
const SSL_METHOD *TLSv1_client_method(void);
Constructor for the TLSv1 SSL_METHOD structure for clients.
const SSL_METHOD *TLSv1_server_method(void);
Constructor for the TLSv1 SSL_METHOD structure for servers.
const SSL_METHOD *SSLv3_method(void);
Constructor for the SSLv3 SSL_METHOD structure for clients, servers
or both.
const SSL_METHOD *SSLv3_client_method(void);
Constructor for the SSLv3 SSL_METHOD structure for clients.
const SSL_METHOD *SSLv3_server_method(void);
Constructor for the SSLv3 SSL_METHOD structure for servers.
const SSL_METHOD *SSLv2_method(void);
Constructor for the SSLv2 SSL_METHOD structure for clients, servers
or both.
const SSL_METHOD *SSLv2_client_method(void);
Constructor for the SSLv2 SSL_METHOD structure for clients.
const SSL_METHOD *SSLv2_server_method(void);
Constructor for the SSLv2 SSL_METHOD structure for servers.
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).
const char *SSL_CIPHER_get_name(SSL_CIPHER *cipher);
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_flush_sessions(SSL_CTX *s, long t);
void SSL_CTX_free(SSL_CTX *a);
char *SSL_CTX_get_app_data(SSL_CTX *ctx);
X509_STORE *SSL_CTX_get_cert_store(SSL_CTX *ctx);
STACK *SSL_CTX_get_client_CA_list(const SSL_CTX *ctx);
int (*SSL_CTX_get_client_cert_cb(SSL_CTX *ctx))(SSL *ssl, X509 **x509,
EVP_PKEY **pkey);
void SSL_CTX_get_default_read_ahead(SSL_CTX *ctx);
char *SSL_CTX_get_ex_data(const SSL_CTX *s, int idx);
int SSL_CTX_get_ex_new_index(long argl, char *argp, int
(*new_func);(void), int (*dup_func)(void), void (*free_func)(void))
void (*SSL_CTX_get_info_callback(SSL_CTX *ctx))(SSL *ssl, int cb, int
ret);
int SSL_CTX_get_quiet_shutdown(const SSL_CTX *ctx);
void SSL_CTX_get_read_ahead(SSL_CTX *ctx);
int SSL_CTX_get_session_cache_mode(SSL_CTX *ctx);
long SSL_CTX_get_timeout(const SSL_CTX *ctx);
int (*SSL_CTX_get_verify_callback(const SSL_CTX *ctx))(int ok,
X509_STORE_CTX *ctx);
int SSL_CTX_get_verify_mode(SSL_CTX *ctx);
int SSL_CTX_load_verify_locations(SSL_CTX *ctx, char *CAfile, char
*CApath);
long SSL_CTX_need_tmp_RSA(SSL_CTX *ctx);
SSL_CTX *SSL_CTX_new(const SSL_METHOD *meth);
int SSL_CTX_remove_session(SSL_CTX *ctx, SSL_SESSION *c);
int SSL_CTX_sess_accept(SSL_CTX *ctx);
int SSL_CTX_sess_accept_good(SSL_CTX *ctx);
int SSL_CTX_sess_accept_renegotiate(SSL_CTX *ctx);
int SSL_CTX_sess_cache_full(SSL_CTX *ctx);
int SSL_CTX_sess_cb_hits(SSL_CTX *ctx);
int SSL_CTX_sess_connect(SSL_CTX *ctx);
int SSL_CTX_sess_connect_good(SSL_CTX *ctx);
int SSL_CTX_sess_connect_renegotiate(SSL_CTX *ctx);
int SSL_CTX_sess_get_cache_size(SSL_CTX *ctx);
SSL_SESSION *(*SSL_CTX_sess_get_get_cb(SSL_CTX *ctx))(SSL *ssl,
unsigned char *data, int len, int *copy);
int (*SSL_CTX_sess_get_new_cb(SSL_CTX *ctx)(SSL *ssl, SSL_SESSION
*sess);
void (*SSL_CTX_sess_get_remove_cb(SSL_CTX *ctx)(SSL_CTX *ctx,
SSL_SESSION *sess);
int SSL_CTX_sess_hits(SSL_CTX *ctx);
int SSL_CTX_sess_misses(SSL_CTX *ctx);
int SSL_CTX_sess_number(SSL_CTX *ctx);
void SSL_CTX_sess_set_cache_size(SSL_CTX *ctx,t);
void SSL_CTX_sess_set_get_cb(SSL_CTX *ctx, SSL_SESSION *(*cb)(SSL *ssl,
unsigned char *data, int len, int *copy));
void SSL_CTX_sess_set_new_cb(SSL_CTX *ctx, int (*cb)(SSL *ssl,
SSL_SESSION *sess));
void SSL_CTX_sess_set_remove_cb(SSL_CTX *ctx, void (*cb)(SSL_CTX *ctx,
SSL_SESSION *sess));
int SSL_CTX_sess_timeouts(SSL_CTX *ctx);
LHASH *SSL_CTX_sessions(SSL_CTX *ctx);
void SSL_CTX_set_app_data(SSL_CTX *ctx, void *arg);
void SSL_CTX_set_cert_store(SSL_CTX *ctx, X509_STORE *cs);
void SSL_CTX_set_cert_verify_cb(SSL_CTX *ctx, int (*cb)(), char *arg)
int SSL_CTX_set_cipher_list(SSL_CTX *ctx, char *str);
void SSL_CTX_set_client_CA_list(SSL_CTX *ctx, STACK *list);
void SSL_CTX_set_client_cert_cb(SSL_CTX *ctx, int (*cb)(SSL *ssl, X509
**x509, EVP_PKEY **pkey));
void SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx, int (*cb);(void))
void SSL_CTX_set_default_read_ahead(SSL_CTX *ctx, int m);
int SSL_CTX_set_default_verify_paths(SSL_CTX *ctx);
int SSL_CTX_set_ex_data(SSL_CTX *s, int idx, char *arg);
void SSL_CTX_set_info_callback(SSL_CTX *ctx, void (*cb)(SSL *ssl, int
cb, int ret));
void SSL_CTX_set_msg_callback(SSL_CTX *ctx, void (*cb)(int write_p, int
version, int content_type, const void *buf, size_t len, SSL *ssl, void
*arg));
void SSL_CTX_set_msg_callback_arg(SSL_CTX *ctx, void *arg);
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_read_ahead(SSL_CTX *ctx, int m);
void SSL_CTX_set_session_cache_mode(SSL_CTX *ctx, int mode);
int SSL_CTX_set_ssl_version(SSL_CTX *ctx, const 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);
X509 *SSL_CTX_get0_certificate(const SSL_CTX *ctx);
EVP_PKEY *SSL_CTX_get0_privatekey(const SSL_CTX *ctx);
void SSL_CTX_set_psk_client_callback(SSL_CTX *ctx, unsigned int
(*callback)(SSL *ssl, const char *hint, char *identity, unsigned int
max_identity_len, unsigned char *psk, unsigned int max_psk_len));
int SSL_CTX_use_psk_identity_hint(SSL_CTX *ctx, const char *hint);
void SSL_CTX_set_psk_server_callback(SSL_CTX *ctx, unsigned int
(*callback)(SSL *ssl, const char *identity, unsigned char *psk, int
max_psk_len));
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);
void SSL_SESSION_set_app_data(SSL_SESSION *s, char *a);
int SSL_SESSION_set_ex_data(SSL_SESSION *s, int idx, char *arg);
long SSL_SESSION_set_time(SSL_SESSION *s, long t);
long SSL_SESSION_set_timeout(SSL_SESSION *s, long t);
DEALING WITH CONNECTIONS
Here we document the various API functions which deal with the SSL/TLS
connection defined in the SSL structure.
int SSL_accept(SSL *ssl);
int SSL_add_dir_cert_subjects_to_stack(STACK *stack, const char *dir);
int SSL_add_file_cert_subjects_to_stack(STACK *stack, const char
*file);
int SSL_add_client_CA(SSL *ssl, X509 *x);
char *SSL_alert_desc_string(int value);
char *SSL_alert_desc_string_long(int value);
char *SSL_alert_type_string(int value);
char *SSL_alert_type_string_long(int value);
int SSL_check_private_key(const SSL *ssl);
void SSL_clear(SSL *ssl);
long SSL_clear_num_renegotiations(SSL *ssl);
int SSL_connect(SSL *ssl);
void SSL_copy_session_id(SSL *t, const SSL *f);
long SSL_ctrl(SSL *ssl, int cmd, long larg, char *parg);
int SSL_do_handshake(SSL *ssl);
SSL *SSL_dup(SSL *ssl);
STACK *SSL_dup_CA_list(STACK *sk);
void SSL_free(SSL *ssl);
SSL_CTX *SSL_get_SSL_CTX(const SSL *ssl);
char *SSL_get_app_data(SSL *ssl);
X509 *SSL_get_certificate(const SSL *ssl);
const char *SSL_get_cipher(const SSL *ssl);
int SSL_get_cipher_bits(const SSL *ssl, int *alg_bits);
char *SSL_get_cipher_list(const SSL *ssl, int n);
char *SSL_get_cipher_name(const SSL *ssl);
char *SSL_get_cipher_version(const SSL *ssl);
STACK *SSL_get_ciphers(const SSL *ssl);
STACK *SSL_get_client_CA_list(const SSL *ssl);
SSL_CIPHER *SSL_get_current_cipher(SSL *ssl);
long SSL_get_default_timeout(const SSL *ssl);
int SSL_get_error(const SSL *ssl, int i);
char *SSL_get_ex_data(const SSL *ssl, int idx);
int SSL_get_ex_data_X509_STORE_CTX_idx(void);
int SSL_get_ex_new_index(long argl, char *argp, int (*new_func);(void),
int (*dup_func)(void), void (*free_func)(void))
int SSL_get_fd(const SSL *ssl);
void (*SSL_get_info_callback(const SSL *ssl);)()
STACK *SSL_get_peer_cert_chain(const SSL *ssl);
X509 *SSL_get_peer_certificate(const SSL *ssl);
EVP_PKEY *SSL_get_privatekey(const SSL *ssl);
int SSL_get_quiet_shutdown(const SSL *ssl);
BIO *SSL_get_rbio(const SSL *ssl);
int SSL_get_read_ahead(const SSL *ssl);
SSL_SESSION *SSL_get_session(const SSL *ssl);
char *SSL_get_shared_ciphers(const SSL *ssl, char *buf, int len);
int SSL_get_shutdown(const SSL *ssl);
const SSL_METHOD *SSL_get_ssl_method(SSL *ssl);
int SSL_get_state(const SSL *ssl);
long SSL_get_time(const SSL *ssl);
long SSL_get_timeout(const SSL *ssl);
int (*SSL_get_verify_callback(const SSL *ssl))(int,X509_STORE_CTX *)
int SSL_get_verify_mode(const SSL *ssl);
long SSL_get_verify_result(const SSL *ssl);
char *SSL_get_version(const SSL *ssl);
BIO *SSL_get_wbio(const SSL *ssl);
int SSL_in_accept_init(SSL *ssl);
int SSL_in_before(SSL *ssl);
int SSL_in_connect_init(SSL *ssl);
int SSL_in_init(SSL *ssl);
int SSL_is_init_finished(SSL *ssl);
STACK *SSL_load_client_CA_file(char *file);
void SSL_load_error_strings(void);
SSL *SSL_new(SSL_CTX *ctx);
long SSL_num_renegotiations(SSL *ssl);
int SSL_peek(SSL *ssl, void *buf, int num);
int SSL_pending(const SSL *ssl);
int SSL_read(SSL *ssl, void *buf, int num);
int SSL_renegotiate(SSL *ssl);
char *SSL_rstate_string(SSL *ssl);
char *SSL_rstate_string_long(SSL *ssl);
long SSL_session_reused(SSL *ssl);
void SSL_set_accept_state(SSL *ssl);
void SSL_set_app_data(SSL *ssl, char *arg);
void SSL_set_bio(SSL *ssl, BIO *rbio, BIO *wbio);
int SSL_set_cipher_list(SSL *ssl, char *str);
void SSL_set_client_CA_list(SSL *ssl, STACK *list);
void SSL_set_connect_state(SSL *ssl);
int SSL_set_ex_data(SSL *ssl, int idx, char *arg);
int SSL_set_fd(SSL *ssl, int fd);
void SSL_set_info_callback(SSL *ssl, void (*cb);(void))
void SSL_set_msg_callback(SSL *ctx, void (*cb)(int write_p, int
version, int content_type, const void *buf, size_t len, SSL *ssl, void
*arg));
void SSL_set_msg_callback_arg(SSL *ctx, void *arg);
void SSL_set_options(SSL *ssl, unsigned long op);
void SSL_set_quiet_shutdown(SSL *ssl, int mode);
void SSL_set_read_ahead(SSL *ssl, int yes);
int SSL_set_rfd(SSL *ssl, int fd);
int SSL_set_session(SSL *ssl, SSL_SESSION *session);
void SSL_set_shutdown(SSL *ssl, int mode);
int SSL_set_ssl_method(SSL *ssl, const SSL_METHOD *meth);
void SSL_set_time(SSL *ssl, long t);
void SSL_set_timeout(SSL *ssl, long t);
void SSL_set_verify(SSL *ssl, int mode, int (*callback);(void))
void SSL_set_verify_result(SSL *ssl, long arg);
int SSL_set_wfd(SSL *ssl, int fd);
int SSL_shutdown(SSL *ssl);
int SSL_state(const SSL *ssl);
char *SSL_state_string(const SSL *ssl);
char *SSL_state_string_long(const SSL *ssl);
long SSL_total_renegotiations(SSL *ssl);
int SSL_use_PrivateKey(SSL *ssl, EVP_PKEY *pkey);
int SSL_use_PrivateKey_ASN1(int type, SSL *ssl, unsigned char *d, long
len);
int SSL_use_PrivateKey_file(SSL *ssl, char *file, int type);
int SSL_use_RSAPrivateKey(SSL *ssl, RSA *rsa);
int SSL_use_RSAPrivateKey_ASN1(SSL *ssl, unsigned char *d, long len);
int SSL_use_RSAPrivateKey_file(SSL *ssl, char *file, int type);
int SSL_use_certificate(SSL *ssl, X509 *x);
int SSL_use_certificate_ASN1(SSL *ssl, int len, unsigned char *d);
int SSL_use_certificate_file(SSL *ssl, char *file, int type);
int SSL_version(const SSL *ssl);
int SSL_want(const SSL *ssl);
int SSL_want_nothing(const SSL *ssl);
int SSL_want_read(const SSL *ssl);
int SSL_want_write(const SSL *ssl);
int SSL_want_x509_lookup(const SSL *ssl);
int SSL_write(SSL *ssl, const void *buf, int num);
void SSL_set_psk_client_callback(SSL *ssl, unsigned int (*callback)(SSL
*ssl, const char *hint, char *identity, unsigned int max_identity_len,
unsigned char *psk, unsigned int max_psk_len));
int SSL_use_psk_identity_hint(SSL *ssl, const char *hint);
void SSL_set_psk_server_callback(SSL *ssl, unsigned int (*callback)(SSL
*ssl, const char *identity, unsigned char *psk, int max_psk_len));
const char *SSL_get_psk_identity_hint(SSL *ssl);
const char *SSL_get_psk_identity(SSL *ssl);
SEE ALSO
openssl(1), crypto(3), SSL_accept(3), SSL_clear(3), SSL_connect(3),
SSL_CIPHER_get_name(3), SSL_COMP_add_compression_method(3),
SSL_CTX_add_extra_chain_cert(3), SSL_CTX_add_session(3),
SSL_CTX_ctrl(3), SSL_CTX_flush_sessions(3),
SSL_CTX_get_ex_new_index(3), SSL_CTX_get_verify_mode(3),
SSL_CTX_load_verify_locations(3) SSL_CTX_new(3),
SSL_CTX_sess_number(3), SSL_CTX_sess_set_cache_size(3),
SSL_CTX_sess_set_get_cb(3), SSL_CTX_sessions(3),
SSL_CTX_set_cert_store(3), SSL_CTX_set_cert_verify_callback(3),
SSL_CTX_set_cipher_list(3), SSL_CTX_set_client_CA_list(3),
SSL_CTX_set_client_cert_cb(3), SSL_CTX_set_default_passwd_cb(3),
SSL_CTX_set_generate_session_id(3), SSL_CTX_set_info_callback(3),
SSL_CTX_set_max_cert_list(3), SSL_CTX_set_mode(3),
SSL_CTX_set_msg_callback(3), SSL_CTX_set_options(3),
SSL_CTX_set_quiet_shutdown(3), SSL_CTX_set_read_ahead(3),
SSL_CTX_set_session_cache_mode(3), SSL_CTX_set_session_id_context(3),
SSL_CTX_set_ssl_version(3), SSL_CTX_set_timeout(3),
SSL_CTX_set_tmp_rsa_callback(3), SSL_CTX_set_tmp_dh_callback(3),
SSL_CTX_set_verify(3), SSL_CTX_use_certificate(3),
SSL_alert_type_string(3), SSL_do_handshake(3), SSL_get_SSL_CTX(3),
SSL_get_ciphers(3), SSL_get_client_CA_list(3),
SSL_get_default_timeout(3), SSL_get_error(3),
SSL_get_ex_data_X509_STORE_CTX_idx(3), SSL_get_ex_new_index(3),
SSL_get_fd(3), SSL_get_peer_cert_chain(3), SSL_get_rbio(3),
SSL_get_session(3), SSL_get_verify_result(3), SSL_get_version(3),
SSL_library_init(3), SSL_load_client_CA_file(3), SSL_new(3),
SSL_pending(3), SSL_read(3), SSL_rstate_string(3),
SSL_session_reused(3), SSL_set_bio(3), SSL_set_connect_state(3),
SSL_set_fd(3), SSL_set_session(3), SSL_set_shutdown(3),
SSL_shutdown(3), SSL_state_string(3), SSL_want(3), SSL_write(3),
SSL_SESSION_free(3), SSL_SESSION_get_ex_new_index(3),
SSL_SESSION_get_time(3), d2i_SSL_SESSION(3),
SSL_CTX_set_psk_client_callback(3), SSL_CTX_use_psk_identity_hint(3),
SSL_get_psk_identity(3)
HISTORY
The ssl(3) document appeared in OpenSSL 0.9.2
1.0.2h 2016-05-03 ssl(3)
SSL_CTX_set_tmp_rsa_callback(3) OpenSSL SSL_CTX_set_tmp_rsa_callback(3)
NAME
SSL_CTX_set_tmp_rsa_callback, SSL_CTX_set_tmp_rsa,
SSL_CTX_need_tmp_rsa, SSL_set_tmp_rsa_callback, SSL_set_tmp_rsa,
SSL_need_tmp_rsa - handle RSA keys for ephemeral key exchange
SYNOPSIS
#include <openssl/ssl.h>
void SSL_CTX_set_tmp_rsa_callback(SSL_CTX *ctx,
RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength));
long SSL_CTX_set_tmp_rsa(SSL_CTX *ctx, RSA *rsa);
long SSL_CTX_need_tmp_rsa(SSL_CTX *ctx);
void SSL_set_tmp_rsa_callback(SSL_CTX *ctx,
RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength));
long SSL_set_tmp_rsa(SSL *ssl, RSA *rsa)
long SSL_need_tmp_rsa(SSL *ssl)
RSA *(*tmp_rsa_callback)(SSL *ssl, int is_export, int keylength);
DESCRIPTION
SSL_CTX_set_tmp_rsa_callback() sets the callback function for ctx to be
used when a temporary/ephemeral RSA key is required to
tmp_rsa_callback. The callback is inherited by all SSL objects newly
created from ctx with <SSL_new(3)|SSL_new(3)>. Already created SSL
objects are not affected.
SSL_CTX_set_tmp_rsa() sets the temporary/ephemeral RSA key to be used
to be rsa. The key is inherited by all SSL objects newly created from
ctx with <SSL_new(3)|SSL_new(3)>. Already created SSL objects are not
affected.
SSL_CTX_need_tmp_rsa() returns 1, if a temporary/ephemeral RSA key is
needed for RSA-based strength-limited 'exportable' ciphersuites because
a RSA key with a keysize larger than 512 bits is installed.
SSL_set_tmp_rsa_callback() sets the callback only for ssl.
SSL_set_tmp_rsa() sets the key only for ssl.
SSL_need_tmp_rsa() returns 1, if a temporary/ephemeral RSA key is
needed, for RSA-based strength-limited 'exportable' ciphersuites
because a RSA key with a keysize larger than 512 bits is installed.
These functions apply to SSL/TLS servers only.
NOTES
When using a cipher with RSA authentication, an ephemeral RSA key
exchange can take place. In this case the session data are negotiated
using the ephemeral/temporary RSA key and the RSA key supplied and
certified by the certificate chain is only used for signing.
Under previous export restrictions, ciphers with RSA keys shorter (512
bits) than the usual key length of 1024 bits were created. To use these
ciphers with RSA keys of usual length, an ephemeral key exchange must
be performed, as the normal (certified) key cannot be directly used.
Using ephemeral RSA key exchange yields forward secrecy, as the
connection can only be decrypted, when the RSA key is known. By
generating a temporary RSA key inside the server application that is
lost when the application is left, it becomes impossible for an
attacker to decrypt past sessions, even if he gets hold of the normal
(certified) RSA key, as this key was used for signing only. The
downside is that creating a RSA key is computationally expensive.
Additionally, the use of ephemeral RSA key exchange is only allowed in
the TLS standard, when the RSA key can be used for signing only, that
is for export ciphers. Using ephemeral RSA key exchange for other
purposes violates the standard and can break interoperability with
clients. It is therefore strongly recommended to not use ephemeral RSA
key exchange and use DHE (Ephemeral Diffie-Hellman) key exchange
instead in order to achieve forward secrecy (see
SSL_CTX_set_tmp_dh_callback(3)).
An application may either directly specify the key or can supply the
key via a callback function. The callback approach has the advantage,
that the callback may generate the key only in case it is actually
needed. As the generation of a RSA key is however costly, it will lead
to a significant delay in the handshake procedure. Another advantage
of the callback function is that it can supply keys of different size
while the explicit setting of the key is only useful for key size of
512 bits to satisfy the export restricted ciphers and does give away
key length if a longer key would be allowed.
The tmp_rsa_callback is called with the keylength needed and the
is_export information. The is_export flag is set, when the ephemeral
RSA key exchange is performed with an export cipher.
EXAMPLES
Generate temporary RSA keys to prepare ephemeral RSA key exchange. As
the generation of a RSA key costs a lot of computer time, they saved
for later reuse. For demonstration purposes, two keys for 512 bits and
1024 bits respectively are generated.
...
/* Set up ephemeral RSA stuff */
RSA *rsa_512 = NULL;
RSA *rsa_1024 = NULL;
rsa_512 = RSA_generate_key(512,RSA_F4,NULL,NULL);
if (rsa_512 == NULL)
evaluate_error_queue();
rsa_1024 = RSA_generate_key(1024,RSA_F4,NULL,NULL);
if (rsa_1024 == NULL)
evaluate_error_queue();
...
RSA *tmp_rsa_callback(SSL *s, int is_export, int keylength)
{
RSA *rsa_tmp=NULL;
switch (keylength) {
case 512:
if (rsa_512)
rsa_tmp = rsa_512;
else { /* generate on the fly, should not happen in this example */
rsa_tmp = RSA_generate_key(keylength,RSA_F4,NULL,NULL);
rsa_512 = rsa_tmp; /* Remember for later reuse */
}
break;
case 1024:
if (rsa_1024)
rsa_tmp=rsa_1024;
else
should_not_happen_in_this_example();
break;
default:
/* Generating a key on the fly is very costly, so use what is there */
if (rsa_1024)
rsa_tmp=rsa_1024;
else
rsa_tmp=rsa_512; /* Use at least a shorter key */
}
return(rsa_tmp);
}
RETURN VALUES
SSL_CTX_set_tmp_rsa_callback() and SSL_set_tmp_rsa_callback() do not
return diagnostic output.
SSL_CTX_set_tmp_rsa() and SSL_set_tmp_rsa() do return 1 on success and
0 on failure. Check the error queue to find out the reason of failure.
SSL_CTX_need_tmp_rsa() and SSL_need_tmp_rsa() return 1 if a temporary
RSA key is needed and 0 otherwise.
SEE ALSO
ssl(3), SSL_CTX_set_cipher_list(3), SSL_CTX_set_options(3),
SSL_CTX_set_tmp_dh_callback(3), SSL_new(3), ciphers(1)
1.0.2h 2016-05-03 SSL_CTX_set_tmp_rsa_callback(3)