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SSL_get_shared_ciphersciphers supported by both client and server

#include <openssl/ssl.h>

char *
SSL_get_shared_ciphers(const SSL *ssl, char *buf, int len);

() puts the names of the ciphers that are supported by both the client and the server of ssl into the buffer buf. Names are separated by colons. At most len bytes are written to buf including the terminating NUL character.

If ssl contains no session, if the session contains no shared ciphers, or if len is less than 2, SSL_get_shared_ciphers() returns NULL. Otherwise, it returns buf.

SSL_get_shared_ciphers() appeared before SSLeay 0.8 and has been available since OpenBSD 2.4.

If the list is too long to fit into len bytes, it is silently truncated after the last cipher name that fits, and all following ciphers are skipped. If the buffer is very short such that even the first cipher name does not fit, an empty string is returned even when some shared ciphers are actually available.

There is no easy way to find out how much space is required for buf or whether the supplied space was sufficient.

March 21, 2018 OpenBSD-6.3