org.cryptimeleon.math.hash.impl

Class VariableOutputLengthHashFunction

java.lang.Object

org.cryptimeleon.math.hash.impl.VariableOutputLengthHashFunction

All Implemented Interfaces:

HashFunction, Representable, StandaloneRepresentable

public class VariableOutputLengthHashFunction
extends java.lang.Object
implements HashFunction, StandaloneRepresentable

A hash function with variable output length.

This class uses an "inner" hash function and applies some tricks to get the output length to what is desired.

If the inner hash function is modeled as a random oracle, the resulting hash function is also a random oracle. If the inner hash function is collision resistant and the desired output length is larger than the inner hash function's output length, then the resulting hash function is also collision resistant.

Constructor Summary

Constructors

Constructor and Description
VariableOutputLengthHashFunction(HashFunction hashFunction, int outputLength) Initializes this instance using a specific base hash function and output length.
VariableOutputLengthHashFunction(int outputLength) Initializes this instance using the SHA256HashFunction and the desired output length.
VariableOutputLengthHashFunction(Representation repr) Reconstructs the hash function from its representation

Method Summary

Modifier and Type	Method and Description
boolean	equals(java.lang.Object obj)
HashFunction	getInnerHashFunction() Retrieves the base hash function to use.
int	getOutputLength() Retrieves the desired output length of this hash function in number of bytes.
Representation	getRepresentation() The representation of this object.
byte[]	hash(byte[] x) Hashes a byte array using the hash function.
int	hashCode()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.cryptimeleon.math.hash.HashFunction

hash, hash

Constructor Detail

VariableOutputLengthHashFunction

public VariableOutputLengthHashFunction(int outputLength)

Initializes this instance using the SHA256HashFunction and the desired output length.

Parameters:

outputLength - the desired output length of this hash function in number of bytes

VariableOutputLengthHashFunction

public VariableOutputLengthHashFunction(HashFunction hashFunction,
                                        int outputLength)

Initializes this instance using a specific base hash function and output length.

Parameters:

hashFunction - the base hash function

outputLength - the desired output length of this hash function in number of bytes

VariableOutputLengthHashFunction

public VariableOutputLengthHashFunction(Representation repr)

Reconstructs the hash function from its representation

Method Detail

getInnerHashFunction

public HashFunction getInnerHashFunction()

Retrieves the base hash function to use.

getRepresentation

public Representation getRepresentation()

Description copied from interface: Representable

The representation of this object. Used for serialization. A convenient way to implement this is using @link ReprUtil

Specified by:

getRepresentation in interface Representable

Returns:

a Representation or null if an equal object can be recreated without any information.

See Also:

Representation

hash

public byte[] hash(byte[] x)

Description copied from interface: HashFunction

Hashes a byte array using the hash function.

Specified by:

hash in interface HashFunction

Parameters:

x - the bytes to hash

Returns:

the hash

getOutputLength

public int getOutputLength()

Retrieves the desired output length of this hash function in number of bytes.

Specified by:

getOutputLength in interface HashFunction

Returns:

the output-length in bytes

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

equals

public boolean equals(java.lang.Object obj)

Overrides:

equals in class java.lang.Object