public static int Decrypt(BigInteger val, PrivateKey privateKey)
{
var m = val % privateKey.Key;
return (int) (m % privateKey.MaxNum);
}
public static int[] DecryptVector(BigInteger[] vector, PrivateKey privateKey)
{
return vector.Select(bi => Decrypt(bi, privateKey)).ToArray();
}
private static BigInteger Decrypt(BigInteger c, PrivateKey privateKey)
{
var m = c % privateKey.Key;
return m % privateKey.MaxNum;
}
public static PublicKey GenPublicKey(PrivateKey privateKey, int bitsCount = DefaultBitsCount)
{
var buff = new BigInteger[DefaultSetSize];
byte[] rand = new byte[bitsCount / 8];
for(int i = 0; i < buff.Length; i++)
{
Singleton.Random.NextBytes(rand);
buff[i] = (BigInteger.Abs(new BigInteger(rand)) * privateKey.Key) + (privateKey.MaxNum * Singleton.Random.Next(10, 100));
}
return new PublicKey { KeyParts = buff, MaxNum = privateKey.MaxNum};
}
public static int[] DecryptVote(this Vote vote, PrivateKey key)
{
if(vote == null || key == null || vote.EncryptedVector == null)
throw new Exception("Can't decrypt vote. Null key or vote");
return vote.EncryptedVector.Select(arg => HomoCrypto.Decrypt(arg, key)).ToArray();
}
public void SaveKey(Guid electionId, PrivateKey privateKey)
{
if(keysWriter == null)
{
lock(keysFilePath)
{
if(keysWriter == null)
keysWriter = new StreamWriter(new FileStream(keysFilePath, FileMode.Append)) { AutoFlush = true };
}
}
keysWriter.WriteLine(new KeyValuePair<Guid, PrivateKey>(electionId, privateKey).ToJsonString());
}
private static string ExtractFlag(Election election, PrivateKey privateKey, int flagLen)
{
if(election.Votes == null)
throw new ServiceException(ExitCode.CORRUPT, "Election has no votes");
if(election.Candidates == null)
throw new ServiceException(ExitCode.CORRUPT, "Election has no candidates");
return string.Join("", election.Votes.Take(flagLen).Select(vote =>
{
var decryptedVote = vote.DecryptVote(privateKey);
int candidateNum = decryptedVote.IndexOf(i => i > 0);
if(candidateNum < 0 || candidateNum >= election.Candidates.Count)
throw new ServiceException(ExitCode.CORRUPT, string.Format("Election has no candidate corresponding to vector {0}", string.Join(",", decryptedVote)));
return election.Candidates[candidateNum].PublicMessage;
}));
}