Secret-key single-message authentication using Poly1305

One-time authentication in Sodium uses Poly1305, a Wegman-Carter authenticator designed by D. J. Bernstein.

Poly1305 takes a 32-byte, one-time key and a message and produces a 16-byte tag that authenticates the message such that an attacker has a negligible chance of producing a valid tag for a inauthentic message.

Keys should never be reused, even with different messages.

Example

const string MESSAGE = "Data to authenticate";
var key = OneTimeAuth.GenerateKey();

//get the authentication code
var signature = OneTimeAuth.Sign(MESSAGE, key);

if (OneTimeAuth.Verify(MESSAGE, signature, key)) {
    //message ok
}

Random Helpers

public static byte[] GenerateKey()

Namespace: Sodium.OneTimeAuth

Uses Sodium.SodiumCore.GetRandomBytes() to generate a 32 byte key.

Usage

Sign

public static byte[] Sign(byte[] message, byte[] key)

//there exists an overloaded version:
public static byte[] Sign(string message, byte[] key)

This is the .NET equivalent of crypto_onetimeauth.

Namespace: Sodium.OneTimeAuth

The Sign() function authenticates a message, with a key.

The key must be 32 bytes, otherwise the function throws a KeyOutOfRangeException.

The function returns a 16 (authenticator) byte array.

Verify

public static bool Verify(byte[] message, byte[] signature, byte[] key)

//there exists an overloaded version:
public static bool Verify(string message, byte[] signature, byte[] key)

This is the .NET equivalent of crypto_onetimeauth_verify.

Namespace: Sodium.OneTimeAuth

The Verify() function verifies a message, with a signature and a key.

The key must be 32 bytes, otherwise the function throws a KeyOutOfRangeException.

The signature must be 16 bytes, otherwise the function throws a SignatureOutOfRangeException.

The function returns true on success, otherwise false.

Algorithm details

• Poly1305