/// <summary>
/// Derives the symmetric key from the shared secret.
/// </summary>
/// <returns>The symmetric key.</returns>
/// <param name="sharedSecret">Shared secret.</param>
private byte[] DeriveSymmetricKeyFromSharedSecret(byte[] sharedSecret)
{
ECDHKekGenerator egH = new ECDHKekGenerator(DigestUtilities.GetDigest("SHA256"));
egH.Init(new DHKdfParameters(NistObjectIdentifiers.Aes, sharedSecret.Length, sharedSecret));
byte[] symmetricKey = new byte[DigestUtilities.GetDigest("SHA256").GetDigestSize()];
egH.GenerateBytes(symmetricKey, 0, symmetricKey.Length);
return(symmetricKey);
}
public static byte[] AsymmetricDecrypt(byte[] data, ref AsymmetricCipherKeyPair keypair)
{
//create the key agreement
ECDHBasicAgreement ag = new ECDHBasicAgreement();
ag.Init(keypair.Private);
//calculate the shared secret key
BigInteger a = ag.CalculateAgreement(keypair.Public);
byte[] secret = a.ToByteArray();
//derive the symmetric encryption key
ECDHKekGenerator topkek = new ECDHKekGenerator(DigestUtilities.GetDigest("SHA256"));
topkek.Init(new DHKdfParameters(NistObjectIdentifiers.Aes, secret.Length, secret));
byte[] symKey = new byte[DigestUtilities.GetDigest("SHA256").GetDigestSize()];
topkek.GenerateBytes(symKey, 0, symKey.Length);
//decrypt the data
KeyParameter parm = ParameterUtilities.CreateKeyParameter("DES", symKey);
IBufferedCipher cipher = CipherUtilities.GetCipher("DES/ECB/ISO7816_4PADDING");
cipher.Init(false, parm);
byte[] ret = null;
try
{
ret = cipher.DoFinal(data);
}
catch (Exception e)
{
if (e != null)
{
return(null);
}
}
//erase the keys
Eraser.SecureErase(secret);
Eraser.SecureErase(symKey);
return(ret);
}
public static byte[] simetricKey(string pvtKey, string pubKey)
{
AsymmetricKeyParameter publicKey = (ECPublicKeyParameters)importKey(ReadOnlyParam.PemWritter.beginPublic + pubKey + ReadOnlyParam.PemWritter.endPublic);
AsymmetricKeyParameter privateKey = ((AsymmetricCipherKeyPair)importKey(ReadOnlyParam.PemWritter.beginPrivate + pvtKey + ReadOnlyParam.PemWritter.endPrivate)).Private;
ECDHCBasicAgreement acAgreement = new ECDHCBasicAgreement();
acAgreement.Init(privateKey);
BigInteger a = acAgreement.CalculateAgreement(publicKey);
byte[] sharedSecret = a.ToByteArray();
ECDHKekGenerator egH = new ECDHKekGenerator(DigestUtilities.GetDigest(ReadOnlyParam.sha));
egH.Init(new DHKdfParameters(NistObjectIdentifiers.Aes, sharedSecret.Length, sharedSecret));
byte[] symmetricKey = new byte[DigestUtilities.GetDigest(ReadOnlyParam.sha).GetDigestSize()];
egH.GenerateBytes(symmetricKey, 0, symmetricKey.Length);
return(symmetricKey);
}
