Curve25519 is an elliptic curve, developed by Dan Bernstein, for fast Diffie-Hellman key agreement.
Ported parts from Java to C# and refactored by Hans Wolff, 17/09/2013.
Original: https://github.com/hanswolff/curve25519/
Ported from C to Java by Dmitry Skiba [sahn0], 23/02/08.
Original: http://code.google.com/p/curve25519-java/
C implementation based on generic 64-bit integer implementation of Curve25519 ECDH
Written by Matthijs van Duin, 200608242056
Original: http://cds.xs4all.nl:8081/ecdh/ (broken link)
Warning! This implementation is susceptible to timing attacks!
// what Alice does
byte[] aliceRandomBytes = new byte[32];
RNGCryptoServiceProvider.Create().GetBytes(aliceRandomBytes);
byte[] alicePrivate = Curve25519.ClampPrivateKey(aliceRandomBytes);
byte[] alicePublic = Curve25519.GetPublicKey(alicePrivate);
// what Bob does
byte[] bobRandomBytes = new byte[32];
RNGCryptoServiceProvider.Create().GetBytes(bobRandomBytes);
byte[] bobPrivate = Curve25519.ClampPrivateKey(bobRandomBytes);
byte[] bobPublic = Curve25519.GetPublicKey(bobPrivate);
// what Alice does with Bob's public key
byte[] aliceShared = Curve25519.GetSharedSecret(alicePrivate, bobPublic);
// what Bob does with Alice' public key
byte[] bobShared = Curve25519.GetSharedSecret(bobPrivate, alicePublic);
// aliceShared == bobShared
...can be downloaded from here:
https://www.nuget.org/packages/Curve25519/
You cannot sign and verify messages with the implementation above. If you need an ECDSA you can use Ed25519.
A good port of Ed25519 can be found here:
https://github.com/CodesInChaos/Chaos.NaCl