CRYPT_CHECKSALT(3) Library Functions Manual CRYPT_CHECKSALT(3)

crypt_checksalt
validate a crypt setting string

Crypt Library (libcrypt, -lcrypt)

#include <crypt.h>

int
crypt_checksalt(const char *setting);

crypt_checksalt checks the setting string against the system configuration and reports whether the hashing method and parameters it specifies are acceptable. It is intended to be used by programs such as login(1) to determine whether the user's passphrase should be re-hashed using the currently preferred hashing method.

The return value is 0 if there is nothing wrong with this setting. Otherwise, it is one of the following constants:
setting is a fully correct setting string. This constant is guaranteed to equal 0.
setting is not a valid setting string; either it specifies a hashing method that is not known to this version of libxcrypt, or it specifies invalid parameters for the method.
setting specifies a hashing method that is no longer allowed to be used at all; crypt will fail if passed this setting. Manual intervention will be required to reactivate the user's account.
setting specifies a hashing method that is no longer considered strong enough for use with new passphrases. crypt will still authenticate a passphrase against this setting, but if authentication succeeds, the passphrase should be re-hashed using the currently preferred method.
setting specifies cost parameters that are considered too cheap for use with new passphrases. crypt will still authenticate a passphrase against this setting, but if authentication succeeds, the passphrase should be re-hashed using the currently preferred method.

<crypt.h> will define the macro CRYPT_CHECKSALT_AVAILABLE if crypt_checksalt is available in the current version of libxcrypt.

Since full configurability is not yet implemented, the current implementation will only ever return CRYPT_SALT_OK (0) or CRYPT_SALT_INVALID when invoked.

The function crypt_checksalt is not part of any standard. It was added to libxcrypt in version 4.3.0.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
Thread safety MT-Safe

crypt(3), crypt_gensalt(3), crypt(5)
November 8, 2018 libxcrypt