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.

Method Summary

byte[]	doFinal(byte[] data) Encrypts or decrypts, depending on the mode already set, a designated array of bytes and returns the result.
byte[]	doFinal(byte[] data, int offset, int length) Encrypts or decrypts, depending on the mode already set, a designated array of bytes and returns the result.
void	init(KDF kdf, 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

init

public void init(KDF kdf,
                 byte[] iv,
                 Direction dir)
          throws SaslException

Initialises a SASL-SRP CALG implementation.

Parameters:

kdf - the key derivation function.

iv - the initial vector value to use.

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

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.

doFinal

public byte[] doFinal(byte[] data,
                      int offset,
                      int length)
               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.

offset - where to start in data.

length - how many bytes to consider in data.

Returns:

the decrypted/encrypted result.

Throws:

ConfidentialityException - if an exception occurs duirng the process.