keygen-cryptographic-proof-verification.cs

using Org.BouncyCastle.Crypto.Signers;
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Digests;
using Org.BouncyCastle.Security;
using System.Text;
using System;

class Program
{
  const string KEYGEN_ACTIVATION_PROOF = "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.U8FwFmcCi_VwbeyPdwW9sH89ehzJhtaRausfNMWof7Q4g5IqysJ2FsrZl6DG5DR50MxI5W69pO9yxmOeaZ_FYZolXTPJtEchjPzB_m9kHh98VdJbuQlu5kwN_bhwL1tgSjyXlirfsAfrWVoqmzmdqpWVaVixkQRzCSflD60icHfQVXsAd2j8LTLcAoufDHwu0iy3Pod-I8oeBSOeK3xjs83BDUQvwSEJtg3wV8YV9ep7htVeqfCLgGijqHZjGW-Im-BP-5yty28OOtp5ad8TJ1s1OtF3HEyu-VWKrI4fTy1btF0OByJbFiz0qAoyOVR6q6GeRshce7iMARomeGS0dg==";
  const string KEYGEN_PUBLIC_KEY = "LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUlJQklqQU5CZ2txaGtpRzl3MEJBUUVGQUFPQ0FROEFNSUlCQ2dLQ0FRRUFyR25RbDhqV3hTcHhkaW9scHhFTQpIU3I2akFhV2Y2NGxvUzNrenBBRGVLWUUwN28rN0I2N2JsNksxbUJqWFNzRzN3eVJJb1dUcEVROFg0RkxydWJqCjNXUC92RXQ5S1FVR1ovbit3azlXaTl2NkQzOXZLS28xWUNEQjVmMlVYOEFTbzB2RGlHQU1NQisvYmwrRHdqR0IKeVpES3BmMDhzcUxJc1RjT3hlUEVWcXNTdlh3cmtIK3czalR5MVlIcTY5MFhrUWVETjBDY3BDNWJEdlFReWF2aAo3anpZVHJzUzNCUjZIN0pPSm1tMFk2ZGh1N2xBQlZQVGpVOTVkaENBQUhUL1FjUHliU3RDMGVrekh0OXFkNFREClMyK2ZoQXJNeWI4ejlEdjdhaFh1eUJxdVMxdnBvUmFJZHZCZTVPWGJTcmt5Z0IzNi93bS9BOWNlK2pCck9qdkUKRHdJREFRQUIKLS0tLS1FTkQgUFVCTElDIEtFWS0tLS0tCg==";

  public static void Main (string[] args)
  {
    var pemPublicKey = Encoding.UTF8.GetString(
      Convert.FromBase64String(KEYGEN_PUBLIC_KEY)
    );

    // Parse and convert the base64 PEM public key to ASN1 format
    var encodedAns1PublicKey = pemPublicKey
        .Replace("-----BEGIN PUBLIC KEY-----", string.Empty)
        .Replace("-----END PUBLIC KEY-----", string.Empty)
        .Trim();
    var asn1PublicKey = Convert.FromBase64String(encodedAns1PublicKey);

    // Import the public key
    var publicKey = PublicKeyFactory.CreateKey(asn1PublicKey);

    // Initialize RSA
    var digest = new Sha256Digest();
    var engine = new RsaEngine();
    var rsa = new RsaDigestSigner(digest);

    rsa.Init(false, publicKey);

    // Parse the activation proof
    var activationProof = KEYGEN_ACTIVATION_PROOF;
    var proofParts = activationProof.Split('.');
    var signingData = proofParts[0];
    var encodedSignature = ConvertBase64UrlString(proofParts[1]);
    var dataParts = signingData.Split('/');
    var signingPrefix = dataParts[0];
    var encodedData = ConvertBase64UrlString(dataParts[1]);

    if (signingPrefix != "proof")
    {
      Console.WriteLine("[ERROR] Invalid activation proof prefix: prefix={0}", signingPrefix);

      Environment.Exit(1);
    }

    // Convert data to bytes for verification
    var signingDataBytes = Encoding.UTF8.GetBytes($"proof/{encodedData}");
    var signatureBytes = Convert.FromBase64String(encodedSignature);

    // Verify the activation proof's signature
    rsa.BlockUpdate(signingDataBytes, 0, signingDataBytes.Length);

    var ok = rsa.VerifySignature(signatureBytes);
    if (ok)
    {
      var decodedDataBytes = Convert.FromBase64String(encodedData);
      var decodedData = Encoding.UTF8.GetString(decodedDataBytes);

      Console.WriteLine("[INFO] Activation proof is cryptographically valid: proof={0} dataset={1}", activationProof, decodedData);

      Environment.Exit(0);
    }
    else
    {
      Console.WriteLine("[ERROR] Activation proof is not valid: proof={0}", activationProof);

      Environment.Exit(1);
    }
  }

  // Cryptographic keys use base64url encoding: https://keygen.sh/docs/api/#license-signatures
  private static string ConvertBase64UrlString(string s)
  {
    return s.Replace("-", "+").Replace("_", "/");
  }
}