auditor
Class Crypto

java.lang.Object
  auditor.Crypto

public class Crypto
extends java.lang.Object

Class responsible for performing cryptographic operations - mainly for checking commitments

Author:

felippo

Field Summary

static javax.crypto.Cipher	cipherNoPaddingNoKey
static javax.crypto.Cipher	cipherPkcs5Padding
(package private) static java.security.MessageDigest	sha

Constructor Summary

Crypto()

Method Summary

static boolean	checkDrowCommitment(java.lang.String slt, int prid, java.lang.String perm, java.lang.String cmt, int partitionID, int instanceID, int rowID, java.lang.String c) Checks if commitment cmt is correct for given data
static boolean	checkProwCommitment(java.lang.String slt, java.lang.String p1, int pid, java.lang.String cmt, java.lang.String c) Checks if cmt is a correct commitment to message (pi, pid) with given salt slt
private static byte[]	computeCommitment(byte[] slt, byte[] c, byte[] m) given a salt slt, election constant c, computes commitment to the message m
static byte[]	computeCommitment(java.lang.String slt, java.lang.String c, byte[] m) Given a message m, salt skm, commitment cmt to m and public constant C it returnes if the commitment to the message m is valid sak=Encrypt C with skm h1 = SHA256(m, sak).
private static byte[]	makeDMessage(byte partitionId, byte instanceId, byte[] rowId, int prid, byte[] perm) Prepares a message for commitment
private static byte[]	makePMessage(byte[] serial, byte[] p) Returns a byte array of "message" for ballot serial and p
protected static byte[]	parse(java.lang.String permutation) Changes permutation string into a byte array

Methods inherited from class java.lang.Object

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

Field Detail

cipherNoPaddingNoKey

public static javax.crypto.Cipher cipherNoPaddingNoKey

cipherPkcs5Padding

public static javax.crypto.Cipher cipherPkcs5Padding

sha

static java.security.MessageDigest sha

Constructor Detail

Crypto

public Crypto()

Method Detail

computeCommitment

public static byte[] computeCommitment(java.lang.String slt,
                                       java.lang.String c,
                                       byte[] m)
                                throws java.lang.Exception

Given a message m, salt skm, commitment cmt to m and public constant C it returnes if the commitment to the message m is valid sak=Encrypt C with skm h1 = SHA256(m, sak). h2 = SHA256(m, Encrypt h1 with sak) the commitment is h1h2 (h1 concatenated with h2) where E stands for Encrypt. The encryption scheme used is AES/ECB/NoPadding

Parameters:

slt - - the salt used in the commitment

m - - the message to be commited to

c - - public constant

Returns:

- commitment to m

Throws:

java.lang.Exception

computeCommitment

private static byte[] computeCommitment(byte[] slt,
                                        byte[] c,
                                        byte[] m)
                                 throws java.lang.Exception

given a salt slt, election constant c, computes commitment to the message m

Parameters:

slt - - salt used in commitment

c - - public constant

m - - message

Returns:

- commitment to m

Throws:

java.lang.Exception

checkProwCommitment

public static boolean checkProwCommitment(java.lang.String slt,
                                          java.lang.String p1,
                                          int pid,
                                          java.lang.String cmt,
                                          java.lang.String c)

Checks if cmt is a correct commitment to message (pi, pid) with given salt slt

Parameters:

slt - - salt

p1 - - message

pid - - p id

cmt - - commitment

c - - public constant

Throws:

java.lang.Exception - if the commitment does not checks.

makePMessage

private static byte[] makePMessage(byte[] serial,
                                   byte[] p)

Returns a byte array of "message" for ballot serial and p

Parameters:

serial - - ballot id

p - - permutation

Returns:

- byte array that represents a message

checkDrowCommitment

public static boolean checkDrowCommitment(java.lang.String slt,
                                          int prid,
                                          java.lang.String perm,
                                          java.lang.String cmt,
                                          int partitionID,
                                          int instanceID,
                                          int rowID,
                                          java.lang.String c)
                                   throws java.lang.Exception

Checks if commitment cmt is correct for given data

Parameters:

slt - - salt

prid - - pid or rid

perm - - permutation (d2 or d4) transformation

cmt - - commitment (cl or cr)

partitionID - - partition id

instanceID - - instance id

c - - public constant

Throws:

java.lang.Exception - if the commitment does not checks. The commitment is constructed using computeCommitment

makeDMessage

private static byte[] makeDMessage(byte partitionId,
                                   byte instanceId,
                                   byte[] rowId,
                                   int prid,
                                   byte[] perm)

Prepares a message for commitment

Parameters:

partitionId - - id of the partition

instanceId - - id ot the instance

rowId - - id of the row

prid - - id (pid or rid)

perm - - permutation (d2 or d4)

Returns:

- byte array that represents a message

parse

protected static byte[] parse(java.lang.String permutation)

Changes permutation string into a byte array

Parameters:

permutation - - string representing permutation

Returns:

- byte array