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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_CLIENT_HELLO_CB(3) OpenSSL SSL_CTX_SET_CLIENT_HELLO_CB(3)

NAME

SSL_CTX_set_client_hello_cb, SSL_client_hello_cb_fn, SSL_client_hello_isv2, SSL_client_hello_get0_legacy_version, SSL_client_hello_get0_random, SSL_client_hello_get0_session_id, SSL_client_hello_get0_ciphers, SSL_client_hello_get0_compression_methods, SSL_client_hello_get1_extensions_present, SSL_client_hello_get0_ext - callback functions for early server-side ClientHello processing

SYNOPSIS

typedef int (*SSL_client_hello_cb_fn)(SSL *s, int *al, void *arg); void SSL_CTX_set_client_hello_cb(SSL_CTX *c, SSL_client_hello_cb_fn *f, void *arg); int SSL_client_hello_isv2(SSL *s); unsigned int SSL_client_hello_get0_legacy_version(SSL *s); size_t SSL_client_hello_get0_random(SSL *s, const unsigned char **out); size_t SSL_client_hello_get0_session_id(SSL *s, const unsigned char **out); size_t SSL_client_hello_get0_ciphers(SSL *s, const unsigned char **out); size_t SSL_client_hello_get0_compression_methods(SSL *s, const unsigned char **out); int SSL_client_hello_get1_extensions_present(SSL *s, int **out, size_t *outlen); int SSL_client_hello_get0_ext(SSL *s, int type, const unsigned char **out, size_t *outlen);

DESCRIPTION

SSL_CTX_set_client_hello_cb() sets the callback function, which is automatically called during the early stages of ClientHello processing on the server. The argument supplied when setting the callback is passed back to the callback at runtime. A callback that returns failure (0) will cause the connection to terminate, and callbacks returning failure should indicate what alert value is to be sent in the al parameter. A callback may also return a negative value to suspend the handshake, and the handshake function will return immediately. SSL_get_error(3) will return SSL_ERROR_WANT_CLIENT_HELLO_CB to indicate that the handshake was suspended. It is the job of the ClientHello callback to store information about the state of the last call if needed to continue. On the next call into the handshake function, the ClientHello callback will be called again, and, if it returns success, normal handshake processing will continue from that point. SSL_client_hello_isv2() indicates whether the ClientHello was carried in a SSLv2 record and is in the SSLv2 format. The SSLv2 format has substantial differences from the normal SSLv3 format, including using three bytes per cipher suite, and not allowing extensions. Additionally, the SSLv2 format 'challenge' field is exposed via SSL_client_hello_get0_random(), padded to SSL3_RANDOM_SIZE bytes with zeros if needed. For SSLv2 format ClientHellos, SSL_client_hello_get0_compression_methods() returns a dummy list that only includes the null compression method, since the SSLv2 format does not include a mechanism by which to negotiate compression. SSL_client_hello_get0_random(), SSL_client_hello_get0_session_id(), SSL_client_hello_get0_ciphers(), and SSL_client_hello_get0_compression_methods() provide access to the corresponding ClientHello fields, returning the field length and optionally setting an out pointer to the octets of that field. Similarly, SSL_client_hello_get0_ext() provides access to individual extensions from the ClientHello on a per-extension basis. For the provided wire protocol extension type value, the extension value and length are returned in the output parameters (if present). SSL_client_hello_get1_extensions_present() can be used prior to SSL_client_hello_get0_ext(), to determine which extensions are present in the ClientHello before querying for them. The out and outlen parameters are both required, and on success the caller must release the storage allocated for *out using OPENSSL_free(). The contents of *out is an array of integers holding the numerical value of the TLS extension types in the order they appear in the ClientHello. *outlen contains the number of elements in the array. In situations when the ClientHello has no extensions, the function will return success with *out set to NULL and *outlen set to 0.

NOTES

The ClientHello callback provides a vast window of possibilities for application code to affect the TLS handshake. A primary use of the callback is to allow the server to examine the server name indication extension provided by the client in order to select an appropriate certificate to present, and make other configuration adjustments relevant to that server name and its configuration. Such configuration changes can include swapping out the associated SSL_CTX pointer, modifying the server's list of permitted TLS versions, changing the server's cipher list in response to the client's cipher list, etc. It is also recommended that applications utilize a ClientHello callback and not use a servername callback, in order to avoid unexpected behavior that occurs due to the relative order of processing between things like session resumption and the historical servername callback. The SSL_client_hello_* family of functions may only be called from code executing within a ClientHello callback.

RETURN VALUES

The application's supplied ClientHello callback returns SSL_CLIENT_HELLO_SUCCESS on success, SSL_CLIENT_HELLO_ERROR on failure, and SSL_CLIENT_HELLO_RETRY to suspend processing. SSL_client_hello_isv2() returns 1 for SSLv2-format ClientHellos and 0 otherwise. SSL_client_hello_get0_random(), SSL_client_hello_get0_session_id(), SSL_client_hello_get0_ciphers(), and SSL_client_hello_get0_compression_methods() return the length of the corresponding ClientHello fields. If zero is returned, the output pointer should not be assumed to be valid. SSL_client_hello_get0_ext() returns 1 if the extension of type 'type' is present, and 0 otherwise. SSL_client_hello_get1_extensions_present() returns 1 on success and 0 on failure.

SEE ALSO

ssl(7), SSL_CTX_set_tlsext_servername_callback(3), SSL_bytes_to_cipher_list

HISTORY

The SSL ClientHello callback, SSL_client_hello_isv2(), SSL_client_hello_get0_random(), SSL_client_hello_get0_session_id(), SSL_client_hello_get0_ciphers(), SSL_client_hello_get0_compression_methods(), SSL_client_hello_get0_ext(), and SSL_client_hello_get1_extensions_present() were added in OpenSSL 1.1.1.

COPYRIGHT

Copyright 2017-2019 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (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>. 1.1.1p 2022-06-21 SSL_CTX_SET_CLIENT_HELLO_CB(3)

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