string crypt(string str, string [salt]);crypt() will encrypt a string using the standard Unix DES encryption method. Arguments are a string to be encrypted and an optional two-character salt string to base the encryption on. See the Unix man page for your crypt function for more information.
If the salt argument is not provided, it will be randomly generated by PHP.
Some operating systems support more than one type of encryption. In fact, sometimes the standard DES 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 2-character DES salt by default unless the default encryption type on the system is MD5 in which case a random MD5-compatible salt is generated.
There is no decrypt function, since crypt() uses a one-way algorithm.