crypt One-way string encryption (hashing) &reftitle.description; stringcrypt stringstr stringsalt crypt will return an encrypted string using the standard Unix DES-based encryption algorithm or alternative algorithms that may be available on the system. Some operating systems support more than one type of encryption. In fact, sometimes the standard DES-based encryption is replaced by an MD5-based encryption algorithm. The encryption type is triggered by the salt argument. At install time, PHP determines the capabilities of the crypt function and will accept salts for other encryption types. If no salt is provided, PHP will auto-generate a standard two character salt by default, unless the default encryption type on the system is MD5, in which case a random MD5-compatible salt is generated. PHP sets a constant named CRYPT_SALT_LENGTH which tells you whether a regular two character salt applies to your system or the longer twelve character salt is applicable. The standard DES-based encryption 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 encryption types, the following constants are set to 0 or 1 depending on whether the given type is available: CRYPT_STD_DES - Standard DES-based encryption with a two character salt CRYPT_EXT_DES - Extended DES-based encryption. 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". CRYPT_MD5 - MD5 encryption with a twelve character salt starting with $1$ CRYPT_BLOWFISH - Blowfish encryption with a salt as follows: "$2a$", a two digit cost parameter, "$", and 22 base 64 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 select DES-based encryption instead, with a salt of '$2'. CRYPT_SHA256 - SHA-256 encryption 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 encryption. 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 encryption 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 encryption. 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 encrypted. salt An optional salt string to base the encryption on. If not provided, one will be randomly generated by PHP each time you call this function. If you are using the supplied salt, you should be aware that the salt is generated once. If you are calling this function repeatedly, this may impact both appearance and security. &reftitle.returnvalues; Returns the encrypted string. &reftitle.changelog; &Version; &Description; 5.3.2 Added SHA-256 and SHA-512 crypt based on Ulrich Drepper's implementation. 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