nc_program_manager/Licensing/LicenseValidator.cs

using System;
using System.Security.Cryptography;
using System.Text;

namespace NcProgramManager.Licensing
{
    internal class LicenseValidator : ILicenseValidator
    {
        // Placeholder — replace with real vendor public key XML after Phase 09 generates the key pair.
        // Generate key pair with the LicenseGenerator tool, then copy the public XML here.
        private const string PublicKeyXml =
            "<RSAKeyValue>" +
            "<Modulus>PLACEHOLDER</Modulus>" +
            "<Exponent>AQAB</Exponent>" +
            "</RSAKeyValue>";

        private readonly string _publicKeyXml;

        // Uses embedded vendor public key.
        internal LicenseValidator() : this(PublicKeyXml) { }

        // Accepts any public key XML — used in unit tests.
        internal LicenseValidator(string publicKeyXml)
        {
            _publicKeyXml = publicKeyXml;
        }

        public bool Validate(string fingerprint, string licenseBase64)
        {
            try
            {
                byte[] signature = Convert.FromBase64String(licenseBase64);
                byte[] data = Encoding.UTF8.GetBytes(fingerprint);
                using (var rsa = new RSACryptoServiceProvider())
                {
                    rsa.FromXmlString(_publicKeyXml);
                    return rsa.VerifyData(data, new SHA256CryptoServiceProvider(), signature);
                }
            }
            catch
            {
                return false;
            }
        }
    }
}