gnu.crypto.sasl.srp
Class CALG

java.lang.Object
  gnu.crypto.sasl.srp.CALG

public final class CALG

extends java.lang.Object

A Factory class that returns CALG (Confidentiality Algorithm) instances that operate as described in the draft-burdis-cat-sasl-srp-08.

The designated CALG block cipher should be used in OFB (Output Feedback Block) mode in the ISO variant, as described in The Handbook of Applied Cryptography, algorithm 7.20.

Let k be the block size of the chosen symmetric key block cipher algorithm; e.g. for AES this is 128 bits or 16 octets. The OFB mode used shall be of length/size k.

It is recommended that block ciphers operating in OFB mode be used with an Initial Vector (the mode's IV). In such a mode of operation - OFB with key re-use - the IV need not be secret. For the mechanism in question the IVs shall be a random octet sequence of k bytes.

The input data to the confidentiality protection algorithm shall be a multiple of the symmetric cipher block size k. When the input length is not a multiple of k octets, the data shall be padded according to the following scheme:

Assuming the length of the input is l octets, (k - (l mod k)) octets, all having the value (k - (l mod k)), shall be appended to the original data. In other words, the input is padded at the trailing end with one of the following sequences:

                    01 -- if l mod k = k-1
                   02 02 -- if l mod k = k-2
                             ...
                             ...
                             ...
                 k k ... k k -- if l mod k = 0

The padding can be removed unambiguously since all input is padded and no padding sequence is a suffix of another. This padding method is well-defined if and only if k < 256 octets, which is the case with symmetric key block ciphers today, and in the forseeable future.

Version:

$Revision: 1.2 $

Method Summary

byte[]	doFinal(byte[] data) Encrypts or decrypts, depending on the mode already set, a designated array of bytes and returns the result.
static CALG	getInstance(java.lang.String algorithm) Returns an instance of a SASL-SRP CALG implementation.
void	init(byte[] K, byte[] iv, Direction dir) Initialises a SASL-SRP CALG implementation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getInstance

public static CALG getInstance(java.lang.String algorithm)

Returns an instance of a SASL-SRP CALG implementation.

Parameters:

algorithm - the name of the symmetric cipher algorithm.

Returns:

an instance of this object.

init

public void init(byte[] K,
                 byte[] iv,
                 Direction dir)
          throws javax.security.sasl.SaslException

Initialises a SASL-SRP CALG implementation.

Parameters:

K - the shared secret.

iv - the initial vector value to use.

dir - whether this CALG is used for encryption or decryption.

Throws:

javax.security.sasl.SaslException

doFinal

public byte[] doFinal(byte[] data)
               throws ConfidentialityException

Encrypts or decrypts, depending on the mode already set, a designated array of bytes and returns the result.

Parameters:

data - the data to encrypt/decrypt

Returns:

the decrypted/encrypted result.

Throws:

ConfidentialityException - if an exception occurs duirng the process.