gnu.crypto.mac

Class TMMH16

Implemented Interfaces:
Cloneable, IMac

public class TMMH16
extends BaseMac
implements Cloneable

TMMH is a universal hash function suitable for message authentication in the Wegman-Carter paradigm, as in the Stream Cipher Security Transform. It is simple, quick, and especially appropriate for Digital Signal Processors and other processors with a fast multiply operation, though a straightforward implementation requires storage equal in length to the largest message to be hashed.

TMMH is a simple hash function which maps a key and a message to a hash value. There are two versions of TMMH: TMMH/16 and TMMH/32. TMMH can be used as a message authentication code, as described in Section 5 (see References).

The key, message, and hash value are all octet strings, and the lengths of these quantities are denoted as KEY_LENGTH, MESSAGE_LENGTH, and TAG_LENGTH, respectively. The values of KEY_LENGTH and TAG_LENGTH MUST be fixed for any particular fixed value of the key, and must obey the alignment restrictions described below.

The parameter MAX_HASH_LENGTH, which denotes the maximum value which MESSAGE_LENGTH may take, is equal to KEY_LENGTH - TAG_LENGTH.

References:

  1. The Truncated Multi-Modular Hash Function (TMMH), David A. McGrew.
Version:
$Revision: 1.6 $

Field Summary

static String
KEYSTREAM
static String
PREFIX
static String
TAG_LENGTH

Fields inherited from class gnu.crypto.mac.BaseMac

name, truncatedSize, underlyingHash

Fields inherited from interface gnu.crypto.mac.IMac

MAC_KEY_MATERIAL, TRUNCATED_SIZE

Constructor Summary

TMMH16()
Trivial 0-arguments constructor.

Method Summary

byte[]
digest()
Completes the MAC by performing final operations such as padding and resetting the instance.
byte[]
digest(IRandom prng)
Similar to the same method with no arguments, but uses the designated random number generator to compute needed keying material.
void
init(Map attributes)
Initialises the algorithm with designated attributes.
int
macSize()
Returns the output length in bytes of this MAC algorithm.
void
reset()
Resets the algorithm instance for re-initialisation and use with other characteristics.
boolean
selfTest()
A basic test.
void
update(byte b)
Continues a MAC operation using the input byte.
void
update(byte b, IRandom prng)
Similar to the same method with one argument, but uses the designated random number generator to compute needed keying material.
void
update(byte[] b, int offset, int len)
Continues a MAC operation, by filling the buffer, processing data in the algorithm's MAC_SIZE-bit block(s), updating the context and count, and buffering the remaining bytes in buffer for the next operation.
void
update(byte[] b, int offset, int len, IRandom prng)
Similar to the same method with three arguments, but uses the designated random number generator to compute needed keying material.

Methods inherited from class gnu.crypto.mac.BaseMac

clone, digest, init, macSize, name, reset, selfTest, update, update

Field Details

KEYSTREAM

public static final String KEYSTREAM

PREFIX

public static final String PREFIX

TAG_LENGTH

public static final String TAG_LENGTH

Constructor Details

TMMH16

public TMMH16()
Trivial 0-arguments constructor.

Method Details

digest

public byte[] digest()
Completes the MAC by performing final operations such as padding and resetting the instance.
Specified by:
digest in interface IMac
Overrides:
digest in interface BaseMac
Returns:
the array of bytes representing the MAC value.

digest

public byte[] digest(IRandom prng)
Similar to the same method with no arguments, but uses the designated random number generator to compute needed keying material.
Parameters:
prng - the source of randomness to use.
Returns:
the final result of the algorithm.

init

public void init(Map attributes)
            throws InvalidKeyException,
                   IllegalStateException
Initialises the algorithm with designated attributes. Permissible names and values are described in the class documentation above.
Specified by:
init in interface IMac
Overrides:
init in interface BaseMac
Parameters:
attributes - a set of name-value pairs that describe the desired future instance behaviour.

macSize

public int macSize()
Returns the output length in bytes of this MAC algorithm.
Specified by:
macSize in interface IMac
Overrides:
macSize in interface BaseMac
Returns:
the output length in bytes of this MAC algorithm.

reset

public void reset()
Resets the algorithm instance for re-initialisation and use with other characteristics. This method always succeeds.
Specified by:
reset in interface IMac
Overrides:
reset in interface BaseMac

selfTest

public boolean selfTest()
A basic test. Ensures that the MAC of a pre-determined message is equal to a known pre-computed value.
Specified by:
selfTest in interface IMac
Overrides:
selfTest in interface BaseMac
Returns:
true if the implementation passes a basic self-test. Returns false otherwise.

update

public void update(byte b)
Continues a MAC operation using the input byte.
Specified by:
update in interface IMac
Overrides:
update in interface BaseMac
Parameters:
b - the input byte to digest.

update

public void update(byte b,
                   IRandom prng)
Similar to the same method with one argument, but uses the designated random number generator to compute needed keying material.
Parameters:
b - the byte to process.
prng - the source of randomness to use.

update

public void update(byte[] b,
                   int offset,
                   int len)
Continues a MAC operation, by filling the buffer, processing data in the algorithm's MAC_SIZE-bit block(s), updating the context and count, and buffering the remaining bytes in buffer for the next operation.
Specified by:
update in interface IMac
Overrides:
update in interface BaseMac
Parameters:
offset - start of meaningful bytes in input block.

update

public void update(byte[] b,
                   int offset,
                   int len,
                   IRandom prng)
Similar to the same method with three arguments, but uses the designated random number generator to compute needed keying material.
Parameters:
b - the byte array to process.
offset - the starting offset in b to start considering the bytes to process.
len - the number of bytes in b starting from offset to process.
prng - the source of randomness to use.

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