public byte[] GetVerifiedSharedPart(byte[] securePart)
{
if (securePart.Length < 4)
{
throw new ArgumentException("Signed part was too short");
}
// Read lengths
ushort publicLength = (ushort)(((ushort)securePart[0]) | ((ushort)securePart[1] << 8));
ushort proofLength = (ushort)(((ushort)securePart[2]) | ((ushort)securePart[3] << 8));
if (securePart.Length != publicLength + proofLength + (sizeof(ushort) * 2))
{
throw new CryptographicException("Part lengths did not match");
}
// Alloc parts
byte[] publicPart = new byte[publicLength];
byte[] proofPart = new byte[proofLength];
// Copy parts
Buffer.BlockCopy(securePart, sizeof(ushort) * 2, publicPart, 0, publicLength);
Buffer.BlockCopy(securePart, sizeof(ushort) * 2 + publicLength, proofPart, 0, proofLength);
if (_isSigner)
{
using (SHA256Managed sha = new SHA256Managed())
{
byte[] claimedHash = _rsa.Decrypt(proofPart, false);
byte[] realHash = sha.ComputeHash(publicPart);
// Prevent timing attacks by using constant time
if (ComparisonUtils.ConstTimeArrayEqual(claimedHash, realHash))
{
return(_diffieHellanInstance.GetSharedSecretRaw(publicPart));
}
else
{
throw new CryptographicException("Hash did not match the signed hash");
}
}
}
else
{
using (SHA256Managed sha = new SHA256Managed())
{
if (_rsa.VerifyData(publicPart, sha, proofPart))
{
return(_diffieHellanInstance.GetSharedSecretRaw(publicPart));
}
else
{
throw new CryptographicException("Signature was invalid");
}
}
}
}
public static void RunECDHE(int iterations)
{
Console.WriteLine("Running " + iterations + " diffie hellman key exchanges");
Stopwatch watch = new Stopwatch();
for (int i = 0; i < iterations; i++)
{
watch.Start();
// Both create their instances
ECDiffieHellman serverDiffie = new ECDiffieHellman();
ECDiffieHellman clientDiffie = new ECDiffieHellman();
// Exchange publics
/* START TRANSMISSION */
byte[] serverPublic = serverDiffie.GetPublicKey();
byte[] clientPublic = clientDiffie.GetPublicKey();
/* END TRANSMISSION */
// Calculate shared
byte[] key1 = serverDiffie.GetSharedSecretRaw(clientPublic);
byte[] key2 = clientDiffie.GetSharedSecretRaw(serverPublic);
watch.Stop();
if (key1.Length != key2.Length)
{
Console.WriteLine("CRITICAL: LENGTH MISSMATCH");
continue;
}
for (int x = 0; x < key1.Length; x++)
{
if (key1[x] != key2[x])
{
Console.WriteLine("CRITICAL: MISSMATCH");
break;
}
}
}
Console.WriteLine("Completed in " + watch.ElapsedMilliseconds + " ms, " + (watch.ElapsedMilliseconds / iterations) + " ms per exchange");
}