gnu.crypto.mac
Class HMac

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

All Implemented Interfaces:

java.lang.Cloneable, IMac

public class HMac

extends BaseMac

The implementation of the HMAC (Keyed-Hash Message Authentication Code).

HMAC can be used in combination with any iterated cryptographic hash function. HMAC also uses a secret key for calculation and verification of the message authentication values. The main goals behind this construction are

• To use, without modifications, available hash functions. In particular, hash functions that perform well in software, and for which code is freely and widely available.
• To preserve the original performance of the hash function without incurring a significant degradation.
• To use and handle keys in a simple way.
• To have a well understood cryptographic analysis of the strength of the authentication mechanism based on reasonable assumptions on the underlying hash function.
• To allow for easy replaceability of the underlying hash function in case that faster or more secure hash functions are found or required.

References:

1. RFC 2104HMAC: Keyed-Hashing for Message Authentication.
   H. Krawczyk, M. Bellare, and R. Canetti.

Version:

$Revision: 1.2 $

Field Summary

protected int	blockSize
protected byte[]	ipad
protected IMessageDigest	ipadHash
protected int	macSize
protected IMessageDigest	opadHash
static java.lang.String	USE_WITH_PKCS5_V2

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

protected

HMac(IMessageDigest underlyingHash) Trivial constructor for use by concrete subclasses.

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) Initialises the algorithm with designated attributes.
void	reset() Resets the algorithm instance for re-initialisation and use with other characteristics.
boolean	selfTest() A basic test.

Methods inherited from class gnu.crypto.mac.BaseMac

macSize, name, update, update

Methods inherited from class java.lang.Object

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

Field Detail

USE_WITH_PKCS5_V2

public static final java.lang.String USE_WITH_PKCS5_V2

See Also:

Constant Field Values

macSize

protected int macSize

blockSize

protected int blockSize

ipadHash

protected IMessageDigest ipadHash

opadHash

protected IMessageDigest opadHash

ipad

protected byte[] ipad

Constructor Detail

HMac

protected HMac(IMessageDigest underlyingHash)

Trivial constructor for use by concrete subclasses.

Parameters:

underlyingHash - the underlying hash algorithm instance.

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

init

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

Description copied from interface: IMac

Initialises the algorithm with designated attributes. Permissible names and values are described in the class documentation above.

Specified by:

init in interface IMac

Specified by:

init in class BaseMac

Throws:

java.security.InvalidKeyException

java.lang.IllegalStateException

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

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

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