libressl-SSL_get_shared_ciphers(3)

libressl-SSL_get_shared_ciphers3

Ciphers supported by both client and server

Usage

SSL Library (libssl, -lssl) libcrypto

#include <openssl/ssl.h>

char *

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

Overview

If ssl contains a session in server mode, SSL_get_shared_ciphers() puts as many names of ciphers that are supported by both the client and the server into the buffer buf as the buffer is long enough to contain. Names are separated by colons. At most len bytes are written to buf including the terminating NUL character.

Return values

SSL_get_shared_ciphers() returns buf on success or NULL on failure. The following situations cause failure:

  • SSL_is_server(3) is false, i.e., ssl is not set to server mode.

  • SSL_get_ciphers(3) is NULL or empty, i.e., no ciphers are available for use by the server.

  • SSL_get_session(3) is NULL, i.e., ssl contains no session.

  • SSL_get_client_ciphers(3) is NULL or empty, i.e., ssl contains no information about ciphers supported by the client, or the client does not support any ciphers.

  • The len argument is less than 2.

History

SSL_get_shared_ciphers() first appeared in SSLeay 0.4.5b and has been available since OpenBSD 2.4.

Bugs

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.

From libressl 4.4.0-1 in Arch Linux 2026-11-01. Parsed by carta from the page's mdoc source.