/// <summary>
/// Randomly generates a secret key and a corresponding public key.
/// </summary>
/// <param name="secretKey">Buffer the secret key will be written to.</param>
/// <param name="publicKey">Buffer the public key will be written to.</param>
/// <exception cref="ArgumentException">thrown if secretKey or publicKey are not 32 bytes long</exception>
public static void KeyPair(Span <byte> secretKey, Span <byte> publicKey)
{
if (secretKey.Length != Curve25519.ScalarLength)
{
throw new ArgumentException("secretKey length must be 32 bytes");
}
if (publicKey.Length != Curve25519.ScalarLength)
{
throw new ArgumentException("publicKey length must be 32 bytes");
}
using var rng = RandomNumberGenerator.Create();
#if NETSTANDARD2_1
rng.GetBytes(secretKey);
#else
var temp = new byte[KeyLength];
rng.GetBytes(temp);
for (int i = 0; i < KeyLength; i++)
{
secretKey[i] = temp[i];
}
Array.Clear(temp, 0, KeyLength);
#endif
Curve25519.ScalarMultiplicationBase(publicKey, secretKey);
}
/// <summary>
/// Create a new Curve25519XSalsa20Poly1305 and pre-calculate the shared secret from secret and public key.
/// </summary>
/// <param name="secretKey">SecretKey</param>
/// <param name="publicKey">PublicKey</param>
public Curve25519XSalsa20Poly1305(ReadOnlySpan <byte> secretKey, ReadOnlySpan <byte> publicKey)
{
ReadOnlySpan <byte> zero = stackalloc byte[16];
Span <byte> s = stackalloc byte[32];
Curve25519.ScalarMultiplication(s, secretKey, publicKey);
HSalsa20.Transform(key, zero, s, Span <byte> .Empty);
s.Clear();
}