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ECDH Key Exchange Examples

Purpose​

The objective of an MTE ECDH "Examples" is to provide a short example of basic MTE Ecdh actions.

Simple demonstration of ECDH within one application.​

using System.Text;

namespace Eclypses.MTE {
  class Program {

    //*******************************************************************
    // Helper function to convert a byte array to a hex string.
    //
    // Overview: convert a byte array to an ASCII hex representation
    // Input:    pointer to the input byte array
    //           length of the input byte array
    //           pointer to the output byte array
    //           size of the output byte array
    // Output:   pointer to the output byte array (convenience result)
    //*******************************************************************
    private static string BytesToHex(byte[] input) {
      const string hex = "0123456789ABCDEF";
      StringBuilder sb = new();
      sb.Clear();
      int i = 0;
      while (i < input.Length) {
        sb.Append(hex[(input[i] >> 4) & 0xF]);
        sb.Append(hex[input[i] & 0xF]);
        i++;
      }
      return sb.ToString();
    }

    private static readonly byte[] publicKeyA = new byte[MteEcdh.SzPublicKey];
    private static readonly byte[] secretA = new byte[MteEcdh.SzSecretData];
    private static readonly byte[] publicKeyB = new byte[MteEcdh.SzPublicKey];
    private static readonly byte[] secretB = new byte[MteEcdh.SzSecretData];

    /*****************************************************
     * Implementation of an application defined callback
     * which is used to generate entropy for ecdhB and
     * also to test the "zeroize" and "getRandom" methods.
     ****************************************************/
    public class EcdhBCallback : IMteEcdhEntropyCallback {
      public int EntropyCallback(byte[] entropyInput) {
        if (entropyInput.Length != MteEcdh.SzPrivateKey)
          return MteEcdh.MemoryFail;
        Array.Fill(entropyInput, (byte)0xCC);
        MteEcdh.Zeroize(entropyInput);
        for (int i = 0; i < entropyInput.Length; i++)
          if (entropyInput[i] != 0)
            return MteEcdh.MemoryFail;
        // Get random bytes.
        byte[] temp = MteRandom.GetBytes((uint)entropyInput.Length);
        if (temp.Length == 0) {
          return MteEcdh.EntropyFail;
        }

        Array.Copy(temp, entropyInput, temp.Length);
        return MteEcdh.Success;
      }
    }

    /*************************************************
     * Main program, loop through all the test vectors
     * and print out results to the console.
     ************************************************/
    static int Main() {

      Console.WriteLine("Ecdh Add-On Demo");

      MteEcdh ecdhA = new();

      // Create key pair for ecdhA.
      if (ecdhA.CreateKeyPair(publicKeyA) != MteEcdh.Success) {
        Console.WriteLine("MteEcdh creating key pair A failed");
        return -1;
      }

      string s = BytesToHex(publicKeyA);
      Console.WriteLine("EcdhA public key:  {0}", s[..MteEcdh.SzPublicKey]);
      Console.WriteLine("                   {0}", s[MteEcdh.SzPublicKey..]);

      // Create key pair for ecdhB.
      MteEcdh ecdhB = new();
      EcdhBCallback ecdhBCallback = new();
      ecdhB.SetEntropyCallback(ecdhBCallback);
      if (ecdhB.CreateKeyPair(publicKeyB) != MteEcdh.Success) {
        Console.WriteLine("MteEcdh creating key pair B failed");
        return -1;
      }

      s = BytesToHex(publicKeyB);
      Console.WriteLine("EcdhB public key:  {0}", s[..MteEcdh.SzPublicKey]);
      Console.WriteLine("                   {0}", s[MteEcdh.SzPublicKey..]);

      // Create secret for ecdhA.
      if (ecdhA.CreateSecret(publicKeyB, secretA) != MteEcdh.Success) {
        Console.WriteLine("MteEcdh creating secret A failed.");
        return -1;
      }
      Console.WriteLine("EcdhA secret:      {0}", BytesToHex(secretA));

      // Create secret for ecdhB.
      if (ecdhB.CreateSecret(publicKeyA, secretB) != MteEcdh.Success) {
        Console.WriteLine("MteEcdh creating secret B failed.");
        return -1;
      }
      Console.WriteLine("EcdhB secret:      {0}", BytesToHex(secretB));

      Console.Write("Pairing secrets:    ");
      if (!secretA.SequenceEqual(secretB)) {
        Console.WriteLine("No match");
        return -1;
      } else {
        Console.WriteLine("Match");
      }

      return 0;
    }
  }
}