spki
Class Hash

java.lang.Object
  |
  +--spki.BaseObj
        |
        +--spki.Hash

public class Hash

extends BaseObj

implements LocObj, Principal, SeqDefName

spki Hash class. A Hash object gives the hash of some other object.

Formal definition:

 <alg-id>:: <byte-string> | <uri> ;
 <hash-alg-id>:: <alg-id> ;
 <hash-value>:: <byte-string> ;
 <hash>:: "(" "hash" <hash-alg-id> <hash-value> <uris>? ")" ;
 

NOTE: For now, only algorithm name is supported for the alg-id.

NOTE: Due to bugs in Cryptix 3.0.3, the MD5 and SHA1 hashing algorithms produce non-comformant output, so we have to use the hashing algorithms provided by Sun. We do not recommend use of other algorithms than MD5 or SHA1.

TODO: support using URI as the alg-id?

Version:

$Id: Hash.java,v 1.29 2002/08/05 18:55:10 tep Exp $

Author:

Tep Narula <tep@win.trlabs.ca>, adapted from SPKI.SPKIHash by Per Harald Myrvang <perm@pasta.cs.uit.no>

Field Summary

private static String	__ME This class's full name.
private String	alg_id The hash algorithm ID.
private MessageDigest	md The digest object used for hashing input values.
static String	SEXP_NAME This class S-Expression type name, used by toSExpression() and other methods.
private URIs	uris The hashed-object's URI, maybe null.
private byte[]	value The hash value.

Fields inherited from class spki.BaseObj

__ME, cache_sexp, cached_sexp, DEFAULT_HASH_ALG, locked, SEXP_NAME

Constructor Summary

protected	Hash() Don't use me!
	Hash(byte[] value, String alg_id, URIs uris) Create an immutable hash object with the specified hashing algorithm and pre-fab hash value.
	Hash(SExpression sexp) Create an immutable Hash object from an S-Expression.
	Hash(String alg_id, byte[] input, URIs uris) Create immutable Hash object from input with the specified hashing algorithm.

Method Summary

boolean	equals(Hash that) Compare this object against the given object.
boolean	equals(Principal that) Compare this object with another principal.
String	getAlgId() Get this object's hashing algorithm ID.
String	getB64Value() Return the hash value as a Base64-encoded string.
private MessageDigest	getMD(String alg_id) Try to get a MessageDigest provider.
byte[]	getValue() Get this object's hash value.
private void	hash(byte[] input) Hash the specified data, store the result, and make this object immutable.
Principal	toHashPrincipal() Convert this principal into a hash representation.
SExpression	toSExpression() Build an SExpression representing this object.

Methods inherited from class spki.BaseObj

disableSExpressionCaching, enableSExpressionCaching, extractHashAlgId, getCachedSExpression, isLocked, isSListOfType, lock, providerToSPKI, setCachedSExpression, spkiToProvider, toString

Methods inherited from class java.lang.Object

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

Field Detail

__ME

private static final String __ME

This class's full name.

SEXP_NAME

public static final String SEXP_NAME

This class S-Expression type name, used by toSExpression() and other methods.

See Also:

toSExpression()

md

private MessageDigest md

The digest object used for hashing input values.

alg_id

private String alg_id

The hash algorithm ID.

value

private byte[] value

The hash value.

uris

private URIs uris

The hashed-object's URI, maybe null.

Constructor Detail

Hash

protected Hash()

Don't use me!

See Also:

Hash(SExpression), Hash(String,byte[],URIs), Hash(byte[],String,URIs)

Hash

public Hash(SExpression sexp)
     throws SPKIException,
            ParseException

Create an immutable Hash object from an S-Expression.

See Also:

BaseObj.BaseObj(SExpression)

Hash

public Hash(String alg_id,
            byte[] input,
            URIs uris)
     throws SPKIException

Create immutable Hash object from input with the specified hashing algorithm.

Parameters:

alg_id - String containing the desired hashing algorithm.

input - Byte array of input data to calculate hash value of.

uris - the hased-object's URI, maybe null.

Throws:

SPKIException - if something went wrong.

Hash

public Hash(byte[] value,
            String alg_id,
            URIs uris)
     throws SPKIException

Create an immutable hash object with the specified hashing algorithm and pre-fab hash value.

Parameters:

alg_id - String containing the desired hashing algorithm.

value - byte array containing the hash-value.

uris - the hased-object's URI, maybe null.

Throws:

SPKIException - if something went wrong.

Method Detail

toSExpression

public SExpression toSExpression()
                          throws SPKIException

Description copied from interface: SPKIObject

Build an SExpression representing this object.

Overrides:

toSExpression in class BaseObj

Tags copied from interface: SPKIObject

Returns:

SExpression object representing this object, or null.

Throws:

SPKIException - if something went wrong during conversion.

equals

public boolean equals(Principal that)

Description copied from interface: Principal

Compare this object with another principal.

Specified by:

equals in interface Principal

Tags copied from interface: Principal

Parameters:

that - a principal to compare with.

Returns:

true if the two principals are equal, false otherwise.

toHashPrincipal

public Principal toHashPrincipal()
                          throws SPKIException

Description copied from interface: Principal

Convert this principal into a hash representation.

Specified by:

toHashPrincipal in interface Principal

Tags copied from interface: Principal

Returns:

the hash representation of this principal.

Throws:

SPKIException - if something went wrong during conversion.

getAlgId

public String getAlgId()

Get this object's hashing algorithm ID.

Returns:

String containing the ID of the hashing hash-alg-id for this object.

getValue

public byte[] getValue()

Get this object's hash value. It makes a copy of the hash value and returns the copy to prevent external tampering.

Returns:

A fresh byte array containing a copy of this object's hash value, or null.

getB64Value

public String getB64Value()

Return the hash value as a Base64-encoded string. TODO: Cache the value?

Returns:

String containing Base64-encoded hash value, or null.

equals

public boolean equals(Hash that)

Compare this object against the given object. NOTE: we don't compare the optional URIs field, though.

Parameters:

that - the Hash object to compare this object against.

Returns:

true if they contain the same hashing algorithm and value, false otherwise.

getMD

private MessageDigest getMD(String alg_id)
                     throws SPKIException

Try to get a MessageDigest provider.

Parameters:

alg_id - String containing the desired algorithm ID.

Returns:

MessageDigest object with specified algorithm.

Throws:

SPKIException - if there were no suitable algorithm

hash

private void hash(byte[] input)
           throws IllegalStateException

Hash the specified data, store the result, and make this object immutable. The input data cannot be chained (i.e. the next call to hash() will throw an exception).

Parameters:

input - Byte array of input data to calculate hash value of.

Throws:

IllegalStateException - if this method is already immutable.

See Also:

getValue(), BaseObj.lock()