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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);

If ssl contains a session in server mode, () 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.

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

ssl(3), SSL_get_ciphers(3)

SSL_get_shared_ciphers() first appeared in SSLeay 0.4.5b 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.

January 9, 2021 OpenBSD-7.3