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Class Crypt


  • public class Crypt
    extends Object
    GNU libc crypt(3) compatible hash method.

    See crypt(String, String) for further details.

    This class is immutable and thread-safe.

    Since:
    1.7
    • Constructor Detail

      • Crypt

        public Crypt()
    • Method Detail

      • crypt

        public static String crypt(byte[] keyBytes,
                                   String salt)
        Encrypts a password in a crypt(3) compatible way.

        If no salt is provided, a random salt and the default algorithm (currently SHA-512) will be used. See crypt(String, String) for details.

        Parameters:
        keyBytes - plaintext password
        salt - real salt value without prefix or "rounds=". The salt may be null, in which case a salt is generated for you using ThreadLocalRandom; for more secure salts consider using SecureRandom to generate your own salts.
        Returns:
        hash value
        Throws:
        IllegalArgumentException - if the salt does not match the allowed pattern
        IllegalArgumentException - when a NoSuchAlgorithmException is caught.
      • crypt

        public static String crypt(String key,
                                   String salt)
        Encrypts a password in a crypt(3) compatible way.

        The exact algorithm depends on the format of the salt string:

        • SHA-512 salts start with $6$ and are up to 16 chars long.
        • SHA-256 salts start with $5$ and are up to 16 chars long
        • MD5 salts start with $1$ and are up to 8 chars long
        • DES, the traditional UnixCrypt algorithm is used with only 2 chars
        • Only the first 8 chars of the passwords are used in the DES algorithm!
        The magic strings "$apr1$" and "$2a$" are not recognized by this method as its output should be identical with that of the libc implementation.

        The rest of the salt string is drawn from the set [a-zA-Z0-9./] and is cut at the maximum length of if a "$" sign is encountered. It is therefore valid to enter a complete hash value as salt to e.g. verify a password with:

         storedPwd.equals(crypt(enteredPwd, storedPwd))
         

        The resulting string starts with the marker string ($n$), where n is the same as the input salt. The salt is then appended, followed by a "$" sign. This is followed by the actual hash value. For DES the string only contains the salt and actual hash. The total length is dependent on the algorithm used:

        • SHA-512: 106 chars
        • SHA-256: 63 chars
        • MD5: 34 chars
        • DES: 13 chars

        Example:

              crypt("secret", "$1$xxxx") => "$1$xxxx$aMkevjfEIpa35Bh3G4bAc."
              crypt("secret", "xx") => "xxWAum7tHdIUw"
         

        This method comes in a variation that accepts a byte[] array to support input strings that are not encoded in UTF-8 but e.g. in ISO-8859-1 where equal characters result in different byte values.

        Parameters:
        key - plaintext password as entered by the used
        salt - real salt value without prefix or "rounds=". The salt may be null, in which case a salt is generated for you using ThreadLocalRandom; for more secure salts consider using SecureRandom to generate your own salts.
        Returns:
        hash value, i.e. encrypted password including the salt string
        Throws:
        IllegalArgumentException - if the salt does not match the allowed pattern
        IllegalArgumentException - when a NoSuchAlgorithmException is caught. *
        See Also:
        "The man page of the libc crypt (3) function."

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