iaik.me.security
Class MessageDigest

java.lang.Object
  |
  +--iaik.me.security.MessageDigest

Direct Known Subclasses:

MD2, MD5, SHA, SHA256

public abstract class MessageDigest

extends Object

This is the main class for digest computation. A message digest is a one-way function that maps an arbitrarily long input to a fixed length output. It can be used in various ways including digital signatures or for MAC functions.

This class defines the API, forms the base class, and is a factory for MessageDigest implementations.

The API closely resembles the API used within the JCE in JDK 1.1 and later, that documentation may provide additional insight.

Note that MessageDigests should not be created directly via the constructor but preferably via the getInstance(String) method defined in this class.
For example:

 MessageDigest digest = MessageDigest.getInstance("SHA1");
 digest.update("MY TEST DATA".getBytes());	
 byte[] result = digest.digest();		
 

Supported algorithm aliases are:

• MD2
• MD5
• SHA
• SHA1
• SHA-1
• SHA-224
• SHA-256

Since:

3.0

Version:

3.02

Field Summary

protected byte[]	buffer Buffer, for use by implementations.
protected long	count Count of the number of bytes processed so far, for use by implementations.
protected int	digestLength
protected static byte[]	padding Data suitable for padding of MD4 style digests. padding[0] == 0x80, all other bytes are zero.

Constructor Summary

protected	MessageDigest(int digestLength) Constructor for implementations that do not which to use the buffering features of this class.
protected	MessageDigest(int digestLength, int blockSize) Constructor for implementations.

Method Summary

abstract Object	clone() Returns a clone of this object.
protected void	compress(byte[] input, int offset) Compression function, to be implemented by subclasses.
byte[]	digest() Computes the digest.
byte[]	digest(byte[] input) Computes the digest.
abstract int	digest(byte[] output, int offset) Performs the final padding operations and computes the digest.
String	getAlgorithm() Returns the name of the used digest algorithm.
int	getDigestLength() Returns the length of the digestalgorithm output in bytes.
abstract byte[][]	getEncodedDigestInfo() Returns the pregenerated ASN1 encoding of the DigestInfo structure for the corresponding digest algorithm, see .
static MessageDigest	getInstance(String algorithm) Returns an instance of the MessageDigest with the given name.
static void	register(String name, String clazz) This method is used to register new (or self implemented) signature algorithms. For example: MessageDigest.register("SHA1", "iaik.me.security.md.SHA"); Once registered, the algorithm can be used via the getInstance(String) method.
abstract void	reset() Resets the internal values of digest instance.
void	update(byte b) Adds a byte to the digest data.
void	update(byte[] input) Adds a byte array to the digest data.
void	update(byte[] input, int offset, int len) Adds a byte array to the digest data.

Methods inherited from class java.lang.Object

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

Field Detail

padding

protected static final byte[] padding

Data suitable for padding of MD4 style digests. padding[0] == 0x80, all other bytes are zero.

digestLength

protected int digestLength

buffer

protected byte[] buffer

Buffer, for use by implementations.

count

protected long count

Count of the number of bytes processed so far, for use by implementations.

Constructor Detail

MessageDigest

protected MessageDigest(int digestLength)

Constructor for implementations that do not which to use the buffering features of this class.

MessageDigest

protected MessageDigest(int digestLength,
                        int blockSize)

Constructor for implementations. Length of digest and block (compression function) are in bytes.

Method Detail

getAlgorithm

public final String getAlgorithm()

Returns the name of the used digest algorithm.

Returns:

the algorithm name

Since:

3.0

getDigestLength

public final int getDigestLength()

Returns the length of the digestalgorithm output in bytes. For e.g. SHA1 has a digestlength of 160 bits, so the resulting digestlength is 20 bytes.

Returns:

the number of bytes of the output

Since:

3.0

update

public void update(byte b)

Adds a byte to the digest data.

Parameters:

b - digest data

Since:

3.0

update

public void update(byte[] input)

Adds a byte array to the digest data.

Since:

3.0

update

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

Adds a byte array to the digest data.

Parameters:

input - the data to be hashed.

offset - startindex

len - number of bytes to be hashed beginnig from the startindex

Since:

3.0

compress

protected void compress(byte[] input,
                        int offset)

Compression function, to be implemented by subclasses.

digest

public abstract int digest(byte[] output,
                           int offset)

Performs the final padding operations and computes the digest. The digest is stored in output, the method itself returns the length of the digest output. The digest instance is automatically reset after the digest was computed.

Parameters:

output - the hash value

offset - starting index of the data to hash

Returns:

the length of the digest output in bytes. see getDigestLength()

Since:

3.0

digest

public final byte[] digest(byte[] input)

Computes the digest. Equivalent to update(byte[]) followed by digest(). This method needs to allocate a new byte array and hence may be less efficient than the digest(byte[] , int ) method if used frequently. The digest instance is automatically reset after the digest was computed.

Parameters:

input - the data to be hashed

Returns:

the computed hashvalue

Since:

3.0

digest

public final byte[] digest()

Computes the digest. This method needs to allocate a new byte array and hence may be less efficient than the digest(byte[] , int ) method if used frequently. The digest instance is automatically reset after the digest was computed.

Returns:

the computed digest

Since:

3.0

reset

public abstract void reset()

Resets the internal values of digest instance. This action is automatically performed after the digest was computed.

Since:

3.0

clone

public abstract Object clone()

Returns a clone of this object. The clone has the exact same state as this object.

Overrides:

clone in class Object

Returns:

the cloned digest object

Since:

3.0

getInstance

public static MessageDigest getInstance(String algorithm)
                                 throws CryptoException

Returns an instance of the MessageDigest with the given name. The name may be an algorithm name (e.g. "MD5") or an object identifier mapped to such a name in the ASN1 class (e.g. ASN.OID_MD5, which is "1.2.840.113549.2.5" and maps to "MD5"). If an implementation is not available (unknown algorithm, implementation not included in JAR file) a CryptoException is thrown. The digest instance is automatically reset after the digest was computed.

Algorithm names supported are MD2, MD5, SHA, SHA1, SHA-1 (alias for SHA), SHA-224, SHA-256 and the object ids registed in the ASN1 class.

Parameters:

algorithm - the name of the digestalgorithm

Returns:

the messagedigest instance

Since:

3.0

getEncodedDigestInfo

public abstract byte[][] getEncodedDigestInfo()

Returns the pregenerated ASN1 encoding of the DigestInfo structure for the corresponding digest algorithm, see . The digest value is of course NOT included. The two dimensional array cotains the enconding with (index = 0) and without the ASN1 parameter NULL (index = 1).

Returns:

a two dimensional byte array containing the digestinfo encodings

Since:

3.04

register

public static void register(String name,
                            String clazz)

This method is used to register new (or self implemented) signature algorithms.
For example:

 MessageDigest.register("SHA1", "iaik.me.security.md.SHA");    
 

Once registered, the algorithm can be used via the getInstance(String) method.

Parameters:

name - the name of the algorithm

clazz - the name of the class which implements the algorithm (with full package name)

Since:

3.0