/// <summary>
/// Encryptes the session key stored in the SessionKey property
/// and saves the results in the EncryptedSessionKey property.
/// </summary>
/// <remarks>This method also calles EncodeSessionKey so that it
/// does not have been called before calling EncryptSessionKey.
/// <p></p>
/// Please note: calling this function takes some time, because
/// asymmetrical encryption takes some time!
/// </remarks>
/// <param name="pkpPacket">An PublicKeyPacket to which
/// the sessionkey should be encrypted to.</param>
public void EncryptSessionKey(PublicKeyPacket pkpPacket)
{
EncodeSessionKey(pkpPacket.KeyMaterial[0].bitCount());
AsymmetricCipher acCipher = new RSA();
switch (aaPublicAlgorithm) {
case AsymAlgorithms.ElGama_Encrypt_Sign:
case AsymAlgorithms.ElGamal_Encrypt_Only:
acCipher = new ElGamal();
break;
case AsymAlgorithms.RSA_Encrypt_Only:
case AsymAlgorithms.RSA_Encrypt_Sign:
acCipher = new RSA();
break;
default:
throw new System.Exception("The chosen public key algorithm is not yet implemented!");
}
this.bIsUpdated = true;
biEncryptedSessionKey = acCipher.Encrypt(new BigInteger(this.bEncodedSessionKey), pkpPacket);
}
private BigInteger[][] GenerateElGamalEncryptionKey(int iKeySize)
{
ElGamal egKeyGenerator = new ElGamal();
BigInteger[][] biEncryptionKey = egKeyGenerator.Generate(iKeySize);
return biEncryptionKey;
}
/// <summary>
/// Decrypts the session key stored in the EncryptedSessionKey
/// property and saves the decrypted key in the EncodedSessionKey
/// property.
/// </summary>
/// <remarks>This function also calls DecodeSessionKey so that the
/// decrypted and decoded sessionkey is stored in the
/// SessionKey property.</remarks>
/// <param name="tskKey">A transportable secret key that is used to
/// decrypt the encrypted session key.</param>
/// <param name="strPassphrase">The passphrase used to decrypt the
/// encrypted key material of the given transportable secret
/// key.</param>
public void DecryptSessionKey(TransportableSecretKey tskKey, string strPassphrase)
{
AsymmetricCipher acCipher = new RSA();
switch (aaPublicAlgorithm) {
case AsymAlgorithms.ElGama_Encrypt_Sign:
case AsymAlgorithms.ElGamal_Encrypt_Only:
acCipher = new ElGamal();
break;
case AsymAlgorithms.RSA_Encrypt_Only:
case AsymAlgorithms.RSA_Encrypt_Sign:
acCipher = new RSA();
break;
default:
throw new System.Exception("The chosen public key algorithm is not yet implemented!");
}
bool bFound = false;
SecretKeyPacket skpKey = new SecretKeyPacket();
IEnumerator ieSubkeys = tskKey.SubKeys.GetEnumerator();
while (ieSubkeys.MoveNext()) {
if (!(ieSubkeys.Current is SecretKeyPacket))
throw new System.Exception("Expected a secret key packet, but did not find one!");
skpKey = (SecretKeyPacket)ieSubkeys.Current;
if (skpKey.PublicKey.KeyID == lKeyID) {
bFound = true;
continue;
}
}
// check if the message was encrypted with the primary key
if (!bFound) {
if (tskKey.PrimaryKey.PublicKey.KeyID == lKeyID) {
skpKey = tskKey.PrimaryKey;
} else {
//theoretically we should never see this exception, as
//encrytped message makes sure we only get fitting secret
//keys, but just in case someone calls this directly, we
//throw an exception
throw new System.Exception("No fitting secret key found!");
}
}
BigInteger biKey = acCipher.Decrypt(this.biEncryptedSessionKey, skpKey, strPassphrase);
this.bEncodedSessionKey = biKey.getBytes();
DecodeSessionKey();
}
