crypt One-way string hashing &reftitle.description; stringcrypt stringstr stringsalt crypt will return a hashed string using the standard Unix DES-based algorithm or alternative algorithms that may be available on the system. Some operating systems support more than one type of hash. In fact, sometimes the standard DES-based algorithm is replaced by an MD5-based algorithm. The hash type is triggered by the salt argument. Prior to 5.3, PHP would determine the available algorithms at install-time based on the system's crypt(). If no salt is provided, PHP will auto-generate either a standard two character (DES) salt, or a twelve character (MD5), depending on the availability of MD5 crypt(). PHP sets a constant named CRYPT_SALT_LENGTH which indicates the longest valid salt allowed by the available hashes. The standard DES-based crypt returns the salt as the first two characters of the output. It also only uses the first eight characters of str, so longer strings that start with the same eight characters will generate the same result (when the same salt is used). On systems where the crypt() function supports multiple hash types, the following constants are set to 0 or 1 depending on whether the given type is available: CRYPT_STD_DES - Standard DES-based hash with a two character salt from the alphabet "./0-9A-Za-z". Using invalid characters in the salt will cause crypt() to fail. CRYPT_EXT_DES - Extended DES-based hash. The "salt" is a 9-character string consisting of an underscore followed by 4 bytes of iteration count and 4 bytes of salt. These are encoded as printable characters, 6 bits per character, least significant character first. The values 0 to 63 are encoded as "./0-9A-Za-z". Using invalid characters in the salt will cause crypt() to fail. CRYPT_MD5 - MD5 hashing with a twelve character salt starting with $1$ CRYPT_BLOWFISH - Blowfish hashing with a salt as follows: "$2a$", a two digit cost parameter, "$", and 22 digits from the alphabet "./0-9A-Za-z". Using characters outside of this range in the salt will cause crypt() to return a zero-length string. The two digit cost parameter is the base-2 logarithm of the iteration count for the underlying Blowfish-based hashing algorithmeter and must be in range 04-31, values outside this range will cause crypt() to fail. CRYPT_SHA256 - SHA-256 hash with a sixteen character salt prefixed with $5$. If the salt string starts with 'rounds=<N>$', the numeric value of N is used to indicate how many times the hashing loop should be executed, much like the cost parameter on Blowfish. The default number of rounds is 5000, there is a minimum of 1000 and a maximum of 999,999,999. Any selection of N outside this range will be truncated to the nearest limit. CRYPT_SHA512 - SHA-512 hash with a sixteen character salt prefixed with $6$. If the salt string starts with 'rounds=<N>$', the numeric value of N is used to indicate how many times the hashing loop should be executed, much like the cost parameter on Blowfish. The default number of rounds is 5000, there is a minimum of 1000 and a maximum of 999,999,999. Any selection of N outside this range will be truncated to the nearest limit. As of PHP 5.3.0, PHP contains its own implementation and will use that if the system lacks of support for one or more of the algorithms. &reftitle.parameters; str The string to be hashed. salt An optional salt string to base the hashing on. If not provided, the behaviour is defined by the algorithm implementation and can lead to unexpected results. &reftitle.returnvalues; Returns the hashed string or a string that is shorter than 13 characters and is guaranteed to differ from the salt on failure. &reftitle.changelog; &Version; &Description; 5.3.2 Added SHA-256 and SHA-512 crypt based on Ulrich Drepper's implementation. 5.3.2 Fixed Blowfish behaviour on invalid rounds to return "failure" string ("*0" or "*1"), instead of falling back to DES. 5.3.0 PHP now contains its own implementation for the MD5 crypt, Standard DES, Extended DES and the Blowfish algorithms and will use that if the system lacks of support for one or more of the algorithms. &reftitle.examples; ]]> ]]> ]]> &example.outputs.similar; &reftitle.notes; There is no decrypt function, since crypt uses a one-way algorithm. &reftitle.seealso; md5 The Mcrypt extension The Unix man page for your crypt function for more information