NAME

SSL_psk_server_cb_func, SSL_psk_find_session_cb_func, SSL_CTX_use_psk_identity_hint, SSL_use_psk_identity_hint, SSL_CTX_set_psk_server_callback, SSL_set_psk_server_callback, SSL_CTX_set_psk_find_session_callback, SSL_set_psk_find_session_callback - set PSK identity hint to use

SYNOPSIS

 #include <openssl/ssl.h>
 
 typedef int (*SSL_psk_find_session_cb_func)(SSL *ssl,
                                             const unsigned char *identity,
                                             size_t identity_len,
                                             SSL_SESSION **sess);
 
 
 void SSL_CTX_set_psk_find_session_callback(SSL_CTX *ctx,
                                            SSL_psk_find_session_cb_func cb);
 void SSL_set_psk_find_session_callback(SSL *s, SSL_psk_find_session_cb_func cb);
 
 typedef unsigned int (*SSL_psk_server_cb_func)(SSL *ssl,
                                                const char *identity,
                                                unsigned char *psk,
                                                unsigned int max_psk_len);
 
 int SSL_CTX_use_psk_identity_hint(SSL_CTX *ctx, const char *hint);
 int SSL_use_psk_identity_hint(SSL *ssl, const char *hint);
 
 void SSL_CTX_set_psk_server_callback(SSL_CTX *ctx, SSL_psk_server_cb_func cb);
 void SSL_set_psk_server_callback(SSL *ssl, SSL_psk_server_cb_func cb);

DESCRIPTION

A server application wishing to use TLSv1.3 PSKs should set a callback using either SSL_CTX_set_psk_find_session_callback() or SSL_set_psk_find_session_callback() as appropriate.

The callback function is given a pointer to the SSL connection in ssl and an identity in identity of length identity_len. The callback function should identify an SSL_SESSION object that provides the PSK details and store it in *sess. The SSL_SESSION object should, as a minimum, set the master key, the ciphersuite and the protocol version. See SSL_session_reused(3) will return true.

RETURN VALUES

SSL_CTX_use_psk_identity_hint() and SSL_use_psk_identity_hint() return 1 on success, 0 otherwise.

Return values from the TLSv1.2 and below server callback are interpreted as follows:

0

PSK identity was not found. An "unknown_psk_identity" alert message will be sent and the connection setup fails.

>0

PSK identity was found and the server callback has provided the PSK successfully in parameter psk. Return value is the length of psk in bytes. It is an error to return a value greater than max_psk_len.

If the PSK identity was not found but the callback instructs the protocol to continue anyway, the callback must provide some random data to psk and return the length of the random data, so the connection will fail with decryption_error before it will be finished completely.

The SSL_psk_find_session_cb_func callback should return 1 on success or 0 on failure. In the event of failure the connection setup fails.

NOTES

There are no known security issues with sharing the same PSK between TLSv1.2 (or below) and TLSv1.3. However the RFC has this note of caution:

"While there is no known way in which the same PSK might produce related output in both versions, only limited analysis has been done. Implementations can ensure safety from cross-protocol related output by not reusing PSKs between TLS 1.3 and TLS 1.2."

COPYRIGHT

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.

OpenSSL.vip