gnu.crypto.mac
Class UMac32

java.lang.Object
  gnu.crypto.mac.BaseMac
      gnu.crypto.mac.UMac32

All Implemented Interfaces:

java.lang.Cloneable, IMac

public class UMac32

extends BaseMac

The implementation of the UMAC (Universal Message Authentication Code).

The UMAC algorithms described are parameterized. This means that various low-level choices, like the endian convention and the underlying cryptographic primitive, have not been fixed. One must choose values for these parameters before the authentication tag generated by UMAC (for a given message, key, and nonce) becomes fully-defined. In this document we provide two collections of parameter settings, and have named the sets UMAC16 and UMAC32. The parameter sets have been chosen based on experimentation and provide good performance on a wide variety of processors. UMAC16 is designed to excel on processors which provide small-scale SIMD parallelism of the type found in Intel's MMX and Motorola's AltiVec instruction sets, while UMAC32 is designed to do well on processors with good 32- and 64- bit support. UMAC32 may take advantage of SIMD parallelism in future processors.

UMAC has been designed to allow implementations which accommodate on-line authentication. This means that pieces of the message may be presented to UMAC at different times (but in correct order) and an on-line implementation will be able to process the message correctly without the need to buffer more than a few dozen bytes of the message. For simplicity, the algorithms in this specification are presented as if the entire message being authenticated were available at once.

To authenticate a message, Msg, one first applies the universal hash function, resulting in a string which is typically much shorter than the original message. The pseudorandom function is applied to a nonce, and the result is used in the manner of a Vernam cipher: the authentication tag is the xor of the output from the hash function and the output from the pseudorandom function. Thus, an authentication tag is generated as

    AuthTag = f(Nonce) xor h(Msg)
 

Here f is the pseudorandom function shared between the sender and the receiver, and h is a universal hash function shared by the sender and the receiver. In UMAC, a shared key is used to key the pseudorandom function f, and then f is used for both tag generation and internally to generate all of the bits needed by the universal hash function.

The universal hash function that we use is called UHASH. It combines several software-optimized algorithms into a multi-layered structure. The algorithm is moderately complex. Some of this complexity comes from extensive speed optimizations.

For the pseudorandom function we use the block cipher of the Advanced Encryption Standard (AES).

The UMAC32 parameters, considered in this implementation are:

                                   UMAC32
                                   ------
        WORD-LEN                        4
        UMAC-OUTPUT-LEN                 8
        L1-KEY-LEN                   1024
        UMAC-KEY-LEN                   16
        ENDIAN-FAVORITE               BIG *
        L1-OPERATIONS-SIGN       UNSIGNED
 

Please note that this UMAC32 differs from the one described in the paper by the ENDIAN-FAVORITE value.

References:

1. UMAC: Message Authentication Code using Universal Hashing.
   T. Krovetz, J. Black, S. Halevi, A. Hevia, H. Krawczyk, and P. Rogaway.

Version:

$Revision: 1.2 $

Field Summary

(package private) static int	KEY_LEN
(package private) static int	L1_KEY_LEN
static java.lang.String	NONCE_MATERIAL Property name of the user-supplied Nonce.
(package private) static int	OUTPUT_LEN

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

UMac32()
Trivial 0-arguments constructor.

Method Summary

java.lang.Object	clone() Returns a clone copy of this instance.
byte[]	digest() Completes the MAC by performing final operations such as padding and resetting the instance.
void	init(java.util.Map attributes) Initialising a UMAC instance consists of defining values for the following parameters: Key Material: as the value of the attribute entry keyed by IMac.MAC_KEY_MATERIAL.
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, 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.

Methods inherited from class gnu.crypto.mac.BaseMac

name

Methods inherited from class java.lang.Object

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

Field Detail

NONCE_MATERIAL

public static final java.lang.String NONCE_MATERIAL

Property name of the user-supplied Nonce. The value associated to this property name is taken to be a byte array.

See Also:

Constant Field Values

OUTPUT_LEN

static final int OUTPUT_LEN

See Also:

Constant Field Values

L1_KEY_LEN

static final int L1_KEY_LEN

See Also:

Constant Field Values

KEY_LEN

static final int KEY_LEN

See Also:

Constant Field Values

Constructor Detail

UMac32

public UMac32()

Trivial 0-arguments constructor.

Method Detail

clone

public java.lang.Object clone()

Description copied from interface: IMac

Returns a clone copy of this instance.

Specified by:

clone in interface IMac

Specified by:

clone in class BaseMac

macSize

public int macSize()

Description copied from interface: IMac

Returns the output length in bytes of this MAC algorithm.

Specified by:

macSize in interface IMac

Overrides:

macSize in class BaseMac

init

public void init(java.util.Map attributes)
          throws java.security.InvalidKeyException,
                 java.lang.IllegalStateException

Initialising a UMAC instance consists of defining values for the following parameters:

1. Key Material: as the value of the attribute entry keyed by IMac.MAC_KEY_MATERIAL. The value is taken to be a byte array containing the user-specified key material. The length of this array, if/when defined SHOULD be exactly equal to KEY_LEN.
2. Nonce Material: as the value of the attribute entry keyed by NONCE_MATERIAL. The value is taken to be a byte array containing the user-specified nonce material. The length of this array, if/when defined SHOULD be (a) greater than zero, and (b) less or equal to 16 (the size of the AES block).

For convenience, this implementation accepts that not both parameters be always specified.

• If the Key Material is specified, but the Nonce Material is not, then this implementation, re-uses the previously set Nonce Material after (a) converting the bytes to an unsigned integer, (b) incrementing the number by one, and (c) converting it back to 16 bytes.
• If the Nonce Material is specified, but the Key Material is not, then this implementation re-uses the previously set Key Material.

This method throws an exception if no Key Material is specified in the input map, and there is no previously set/defined Key Material (from an earlier invocation of this method). If a Key Material can be used, but no Nonce Material is defined or previously set/defined, then a default value of all-zeroes shall be used.

Specified by:

init in interface IMac

Specified by:

init in class BaseMac

Parameters:

attributes - one or both of required parameters.

Throws:

java.security.InvalidKeyException - the key material specified is not of the correct length.

java.lang.IllegalStateException

update

public void update(byte b)

Description copied from interface: IMac

Continues a MAC operation using the input byte.

Specified by:

update in interface IMac

Overrides:

update in class BaseMac

update

public void update(byte[] b,
                   int offset,
                   int len)

Description copied from interface: IMac

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 class BaseMac

digest

public byte[] digest()

Description copied from interface: IMac

Completes the MAC by performing final operations such as padding and resetting the instance.

Specified by:

digest in interface IMac

Specified by:

digest in class BaseMac

reset

public void reset()

Description copied from interface: IMac

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 class BaseMac

selfTest

public boolean selfTest()

Description copied from interface: IMac

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

Specified by:

selfTest in class BaseMac