paillierp.key
Class PaillierPrivateKey

java.lang.Object
  paillierp.key.PaillierKey
      paillierp.key.PaillierPrivateKey

All Implemented Interfaces:

java.io.Serializable

public class PaillierPrivateKey
extends PaillierKey

A simple private key for the generalized Paillier cryptosystem CS₁.

The private key for the generalized Paillier cryptosystem CS_s constructed in Damgård et al. requires the public key values of n and g (as provided for in PaillierKey), and the secret value d as defined as follows:

• d is an element such that d mod n ∈ Z^*_n and d = 0 mod λ where λ=lcm(p-1,q-1).

Version:

1.0 03/25/10

Author:

James Garrity, Sean Hall

See Also:

PaillierKey, Serialized Form

Field Summary

protected java.math.BigInteger	d Secret key; d mod n∈Z*n and d = 0 mod λ, where λ is least common multiple of p-1 and q-1.
protected java.math.BigInteger	dInvs The inverse of d mod ns.
private static long	serialVersionUID This Serial ID

Fields inherited from class paillierp.key.PaillierKey

k, MAX_KEY_SIZE, n, nPlusOne, ns, nSPlusOne, rnd

Constructor Summary

PaillierPrivateKey(java.math.BigInteger p, java.math.BigInteger q, java.math.BigInteger d, long seed)
Creates a new private key when given the primes p and q and the secret value d.

PaillierPrivateKey(java.math.BigInteger n, java.math.BigInteger d, long seed)
Creates a new private key when given the modulus n and the secret value d.

PaillierPrivateKey(byte[] b, long seed)
Creates a new private key using a byte encoding of a key.

Method Summary

boolean	canEncrypt() Describes if this key can be used to encrypt
java.math.BigInteger	getD() Accesses the secret integer d chosen at the creation of this secret key.
java.math.BigInteger	getDInvs() Access the precomputed inverse of d in Z*ns+1.
byte[]	toByteArray() Encodes this key into a byte array.
java.math.BigInteger[]	toIntArray() Returns a BigInt array corresponding to this Paillier pubilc key.

Methods inherited from class paillierp.key.PaillierKey

getK, getN, getNPlusOne, getNS, getNSPlusOne, getPublicKey, getRandomModN, getRandomModNSPlusOneStar, getRandomModNStar, getRnd, inModN, inModN, inModNS, inModNSPlusOne, inModNSPlusOneStar, inModNStar, inModNStar, isCiphertext, isPlaintext, setRnd, setRnd, updateRnd

Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

private static final long serialVersionUID

This Serial ID

See Also:

Constant Field Values

d

protected java.math.BigInteger d

Secret key; d mod n∈Z^*_n and d = 0 mod λ, where λ is least common multiple of p-1 and q-1.

dInvs

protected java.math.BigInteger dInvs

The inverse of d mod n^s. Used in the final step of decryption.

Constructor Detail

PaillierPrivateKey

public PaillierPrivateKey(java.math.BigInteger n,
                          java.math.BigInteger d,
                          long seed)

Creates a new private key when given the modulus n and the secret value d. This constructor will use the seed to create the public key with a SecureRandom random number generator.

Parameters:

n - a RSA modulus. That is, the product of two different odd primes p, q.

d - an integer that should be a multiple of the least common multiple of p-1 and q-1, and relatively prime to n

seed - a long integer needed to start a random number generator

PaillierPrivateKey

public PaillierPrivateKey(java.math.BigInteger p,
                          java.math.BigInteger q,
                          java.math.BigInteger d,
                          long seed)

Creates a new private key when given the primes p and q and the secret value d. This constructor will use the seed to create the public key with a SecureRandom random number generator.

Parameters:

p - one allowable prime for our modulus

q - another prime for our modulus, different from

d - an integer that should be a multiple of the least common multiple of p-1 and q-1, and relatively prime to p*q

seed - a long integer needed to start a random number generator

PaillierPrivateKey

public PaillierPrivateKey(byte[] b,
                          long seed)

Creates a new private key using a byte encoding of a key.

Parameters:

b - Byte array of the necessary values of this private key

seed - a long integer needed to start a random number generator

See Also:

toByteArray()

Method Detail

canEncrypt

public boolean canEncrypt()

Describes if this key can be used to encrypt

Overrides:

canEncrypt in class PaillierKey

Returns:

'true' if it can encrypt.

getD

public java.math.BigInteger getD()

Accesses the secret integer d chosen at the creation of this secret key. In the generalized Paillier cryptosystem, ciphertext E(i,r) raised to the d power will result in (1+n)^{jid mod ns}. Applying a method, one can easily find jid and jd, allowing one to find i mod n^s. Note that in our simplified version, both s and j are 1.

Returns:

the secret integer that allows decryption

getDInvs

public java.math.BigInteger getDInvs()

Access the precomputed inverse of d in Z^*_n^s+1. This allows one to decrypt a little more expediently.

Returns:

the inverse of d in mod n²

See Also:

getD()

toIntArray

public java.math.BigInteger[] toIntArray()

Returns a BigInt array corresponding to this Paillier pubilc key.

toByteArray

public byte[] toByteArray()

Encodes this key into a byte array. As this is a public key, the public modulo n, d will be encoded in that order. Further, before d is the 4-byte equivalent to the size of the BigInteger for later parsing.

Overrides:

toByteArray in class PaillierKey

Returns:

a byte array containing the most necessary values of this key. A byte array of size 0 is returned if the key would be too large.

See Also:

PaillierPrivateKey(byte[], long), BigInteger.toByteArray()