|gnutls_priority_t * priority_cache||is a gnutls_prioritity_t type.|
|const char * priorities||is a string describing priorities (may be NULL)|
|const char ** err_pos||In case of an error this will have the position in the string the error occurred|
Sets priorities for the ciphers, key exchange methods, macs and compression methods. The priority_cache should be deinitialized using gnutls_priority_deinit().
The priorities option allows you to specify a colon separated list of the cipher priorities to enable. Some keywords are defined to provide quick access to common preferences.
Unless there is a special need, use the "NORMAL" keyword to apply a reasonable security level, or "NORMAL:COMPAT" for compatibility.
"PERFORMANCE" means all the "secure" ciphersuites are enabled, limited to 128 bit ciphers and sorted by terms of speed performance.
"LEGACY" the NORMAL settings for GnuTLS 3.2.x or earlier. There is no verification profile set, and the allowed DH primes are considered weak today.
"NORMAL" means all "secure" ciphersuites. The 256-bit ciphers are included as a fallback only. The ciphers are sorted by security margin.
"PFS" means all "secure" ciphersuites that support perfect forward secrecy. The 256-bit ciphers are included as a fallback only. The ciphers are sorted by security margin.
"SECURE128" means all "secure" ciphersuites of security level 128-bit or more.
"SECURE192" means all "secure" ciphersuites of security level 192-bit or more.
"SUITEB128" means all the NSA SuiteB ciphersuites with security level of 128.
"SUITEB192" means all the NSA SuiteB ciphersuites with security level of 192.
"NONE" means nothing is enabled. This disables even protocols and compression methods.
" KEYWORD " The system administrator imposed settings. The provided keywords will be expanded from a configuration-time provided file - default is: /etc/gnutls/default-priorities. Any keywords that follow it, will be appended to the expanded string. If there is no system string, then the function will fail. The system file should be formatted as "KEYWORD=VALUE", e.g., "SYSTEM=NORMAL:+ARCFOUR-128".
Special keywords are "!", "-" and "+". "!" or "-" appended with an algorithm will remove this algorithm. "+" appended with an algorithm will add this algorithm.
Check the GnuTLS manual section "Priority strings" for detailed information.
"NORMAL:+ARCFOUR-128" means normal ciphers plus ARCFOUR-128.
"SECURE128:-VERS-SSL3.0:+COMP-DEFLATE" means that only secure ciphers are enabled, SSL3.0 is disabled, and libz compression enabled.
Note that "NORMAL:COMPAT" is the most compatible mode.
A NULL priorities string indicates the default priorities to be used (this is available since GnuTLS 3.3.0).
On syntax error GNUTLS_E_INVALID_REQUEST is returned, GNUTLS_E_SUCCESS on success, or an error code.
Report bugs to <firstname.lastname@example.org>.
Home page: http://www.gnutls.org
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