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@deftypefun {int} {gnutls_priority_init} (gnutls_priority_t * @var{priority_cache}, const char * @var{priorities}, const char ** @var{err_pos})
@var{priority_cache}: is a @code{gnutls_prioritity_t} structure.
@var{priorities}: is a string describing priorities
@var{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 @code{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:@code{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.
"EXPORT" means all ciphersuites are enabled, including the
low-security 40 bit ciphers.
"NONE" means nothing is enabled. This disables even protocols and
compression methods.
" @code{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.
@strong{Examples:}
"NONE:+VERS-TLS-ALL:+MAC-ALL:+RSA:+AES-128-CBC:+SIGN-ALL:+COMP-NULL"
"NORMAL:-ARCFOUR-128" means normal ciphers except for ARCFOUR-128.
"SECURE128:-VERS-SSL3.0:+COMP-DEFLATE" means that only secure ciphers are
enabled, SSL3.0 is disabled, and libz compression enabled.
"NONE:+VERS-TLS-ALL:+AES-128-CBC:+RSA:+SHA1:+COMP-NULL:+SIGN-RSA-SHA1",
"NONE:+VERS-TLS-ALL:+AES-128-CBC:+ECDHE-RSA:+SHA1:+COMP-NULL:+SIGN-RSA-SHA1:+CURVE-SECP256R1",
"SECURE256:+SECURE128",
Note that "NORMAL:@code{COMPAT} " is the most compatible mode.
@strong{Returns:} On syntax error @code{GNUTLS_E_INVALID_REQUEST} is returned,
@code{GNUTLS_E_SUCCESS} on success, or an error code.
@end deftypefun
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