org.bitpedia.util

Class Sha1

java.lang.Object

java.security.MessageDigestSpi

java.security.MessageDigest

org.bitpedia.util.Sha1

All Implemented Interfaces:

java.lang.Cloneable

public final class Sha1
extends java.security.MessageDigest
implements java.lang.Cloneable

The FIPS PUB 180-2 standard specifies four secure hash algorithms (SHA-1, SHA-256, SHA-384 and SHA-512) for computing a condensed representation of electronic data (message). When a message of any length < 2^^64 bits (for SHA-1 and SHA-256) or < 2^^128 bits (for SHA-384 and SHA-512) is input to an algorithm, the result is an output called a message digest. The message digests range in length from 160 to 512 bits, depending on the algorithm. Secure hash algorithms are typically used with other cryptographic algorithms, such as digital signature algorithms and keyed-hash message authentication codes, or in the generation of random numbers (bits).

The four hash algorithms specified in this "SHS" standard are called secure because, for a given algorithm, it is computationally infeasible 1) to find a message that corresponds to a given message digest, or 2) to find two different messages that produce the same message digest. Any change to a message will, with a very high probability, result in a different message digest. This will result in a verification failure when the secure hash algorithm is used with a digital signature algorithm or a keyed-hash message authentication algorithm.

A "SHS change notice" adds a SHA-224 algorithm for interoperability, which, like SHA-1 and SHA-256, operates on 512-bit blocks and 32-bit words, but truncates the final digest and uses distinct initialization values.

References:

1. NIST FIPS PUB 180-2, "Secure Hash Signature Standard (SHS) with change notice", National Institute of Standards and Technology (NIST), 2002 August 1, and U.S. Department of Commerce, August 26.
   http://csrc.ncsl.nist.gov/CryptoToolkit/Hash.html
2. NIST FIPS PUB 180-1, "Secure Hash Standard", U.S. Department of Commerce, May 1993.
   http://www.itl.nist.gov/div897/pubs/fip180-1.htm
3. Bruce Schneier, "Section 18.7 Secure Hash Algorithm (SHA)", Applied Cryptography, 2nd edition,
   John Wiley & Sons, 1996

Field Summary

Fields

Modifier and Type	Field and Description
static int	HASH_LENGTH This implementation returns a fixed-size digest.

Constructor Summary

Constructors

Constructor and Description
Sha1() Creates a SHA1 object with default initial state.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	clone() Clones this object.
byte[]	engineDigest() Completes the hash computation by performing final operations such as padding.
int	engineDigest(byte[] hashvalue, int offset, int len) Completes the hash computation by performing final operations such as padding.
int	engineGetDigestLength() Returns the digest length in bytes.
protected void	engineReset() Reset athen initialize the digest context.
void	engineUpdate(byte input) Updates the digest using the specified byte.
void	engineUpdate(byte[] input, int offset, int len) Updates the digest using the specified array of bytes, starting at the specified offset.
protected void	init() Initialize the digest context.

Methods inherited from class java.security.MessageDigest

digest, digest, digest, getAlgorithm, getDigestLength, getInstance, getInstance, getInstance, getProvider, isEqual, reset, toString, update, update, update, update

Methods inherited from class java.security.MessageDigestSpi

engineUpdate

Methods inherited from class java.lang.Object

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

Field Detail

HASH_LENGTH

public static final int HASH_LENGTH

This implementation returns a fixed-size digest.

See Also:

Constant Field Values

Constructor Detail

Sha1

public Sha1()

Creates a SHA1 object with default initial state.

Method Detail

clone

public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException

Clones this object.

Overrides:

clone in class java.security.MessageDigest

Throws:

java.lang.CloneNotSupportedException

engineGetDigestLength

public int engineGetDigestLength()

Returns the digest length in bytes. Can be used to allocate your own output buffer when computing multiple digests. Overrides the protected abstract method of java.security.MessageDigestSpi.

Overrides:

engineGetDigestLength in class java.security.MessageDigestSpi

Returns:

the digest length in bytes.

engineReset

protected void engineReset()

Reset athen initialize the digest context. Overrides the protected abstract method of java.security.MessageDigestSpi.

Specified by:

engineReset in class java.security.MessageDigestSpi

init

protected void init()

Initialize the digest context.

engineUpdate

public void engineUpdate(byte input)

Updates the digest using the specified byte. Requires internal buffering, and may be slow. Overrides the protected abstract method of java.security.MessageDigestSpi.

Specified by:

engineUpdate in class java.security.MessageDigestSpi

Parameters:

input - the byte to use for the update.

engineUpdate

public void engineUpdate(byte[] input,
                         int offset,
                         int len)

Updates the digest using the specified array of bytes, starting at the specified offset. Input length can be any size. May require internal buffering, if input blocks are not multiple of 64 bytes. Overrides the protected abstract method of java.security.MessageDigestSpi.

Specified by:

engineUpdate in class java.security.MessageDigestSpi

Parameters:

input - the array of bytes to use for the update.

offset - the offset to start from in the array of bytes.

len - the number of bytes to use, starting at offset.

engineDigest

public byte[] engineDigest()

Completes the hash computation by performing final operations such as padding. Computes the final hash and returns the final value as a byte[20] array. Once engineDigest has been called, the engine will be automatically reset as specified in the JavaSecurity MessageDigest specification. For faster operations with multiple digests, allocate your own array and use engineDigest(byte[], int offset, int len). Overrides the protected abstract method of java.security.MessageDigestSpi.

Specified by:

engineDigest in class java.security.MessageDigestSpi

Returns:

the length of the digest stored in the output buffer.

engineDigest

public int engineDigest(byte[] hashvalue,
                        int offset,
                        int len)
                 throws java.security.DigestException

Completes the hash computation by performing final operations such as padding. Once engineDigest has been called, the engine will be automatically reset (see engineReset). Overrides the protected abstract method of java.security.MessageDigestSpi.

Overrides:

engineDigest in class java.security.MessageDigestSpi

Parameters:

hashvalue - the output buffer in which to store the digest.

offset - offset to start from in the output buffer

len - number of bytes within buf allotted for the digest. Both this default implementation and the SUN provider do not return partial digests. The presence of this parameter is solely for consistency in our API's. If the value of this parameter is less than the actual digest length, the method will throw a DigestException. This parameter is ignored if its value is greater than or equal to the actual digest length.

Returns:

the length of the digest stored in the output buffer.

Throws:

java.security.DigestException