Ubuntu Manpage: gnutls_priority_init

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Provided by: gnutls-doc_3.5.18-1ubuntu1.6_all

NAME

       gnutls_priority_init - API function

SYNOPSIS

       #include <gnutls/gnutls.h>

       int  gnutls_priority_init(gnutls_priority_t  *  priority_cache,  const  char  * priorities, const char **
       err_pos);

ARGUMENTS

       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

DESCRIPTION

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.

"@KEYWORD1,KEYWORD2,..." The system administrator imposed settings. The provided keyword(s) will be
expanded from a configuration-time provided file - default is: /etc/gnutls/default-priorities. Any
attributes that follow it, will be appended to the expanded string. If multiple keywords are provided,
separated by commas, then the first keyword that exists in the configuration file will be used. At least
one of the keywords must exist, or this function will return an error. Typical usage would be to specify
an application specified keyword first, followed by "SYSTEM" as a default fallback. e.g., " LIBVIRT
,SYSTEM:!-VERS-SSL3.0" will first try to find a config file entry matching "LIBVIRT", but if that does
not exist will use the entry for "SYSTEM". If "SYSTEM" does not exist either, an error will be returned.
In all cases, the SSL3.0 protocol will be disabled. The system priority file entries 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.

EXAMPLES

       "NONE:+VERS-TLS-ALL:+MAC-ALL:+RSA:+AES-128-CBC:+SIGN-ALL:+COMP-NULL"

       "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.

       "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:%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).

RETURNS

       On syntax error GNUTLS_E_INVALID_REQUEST is returned, GNUTLS_E_SUCCESS on success, or an error code.

REPORTING BUGS

       Report bugs to <bugs@gnutls.org>.
       Home page: http://www.gnutls.org

COPYRIGHT

       Copyright © 2001-2022 Free Software Foundation, Inc., and others.
       Copying  and distribution of this file, with or without modification, are permitted in any medium without
       royalty provided the copyright notice and this notice are preserved.