sharee.bike-App/LockItShared/Services/BluetoothLock/Crypto/AuthCryptoHelper.cs

using Serilog;
using TINK.Model.Device;

namespace TINK.Services.BluetoothLock.Crypto
{
    public class AuthCryptoHelper
    {
        private ICipher Cipher { get; }

        /// <summary> Encrypted seed (random number) created inside ILOCKIT and passd to app.</summary>
        private byte[] SeedLockEncrypted { get; }

        /// <summary> Contstructs a auth crypto helper object.</summary>
        /// <param name="seedLockEncrypted">Encrypted seed to deocode using <see cref="KeyCopri"/>.</param>
        /// <param name="keyCopri">Key used to to decrypt <see cref="SeedLockEncrypted"/>.</param>
        public AuthCryptoHelper(
             byte[] seedLockEncrypted,
             byte[] keyCopri,
             ICipher cipher)
        {
            KeyCopri = keyCopri;
            SeedLockEncrypted = seedLockEncrypted;
            Cipher = cipher ?? new Cipher();
        }


        /// <summary> Public for testing purposes only.</summary>
        public byte[] GetSeedLock()
        {
            byte[] seedLockDecrypted;
            var seedLockEncrypted = SeedLockEncrypted;
            var keyCopri = KeyCopri;
            try
            {
                seedLockDecrypted = Cipher.Decrypt(
                        keyCopri,
                        seedLockEncrypted);
            }
            catch (System.Exception exception)
            {
                Log.ForContext<AuthCryptoHelper>().Error("Decrypting seed from lock failed. {Exception}", exception);
                throw;
            }

            Log.ForContext<AuthCryptoHelper>().Verbose($"Lock random number decrypted from {string.Join(",", seedLockEncrypted)} to {string.Join(",", seedLockDecrypted)} using {string.Join(", ", keyCopri)}.");
            return seedLockDecrypted;
        }

        public byte[] GetAccessKeyEncrypted()
        {

            var accessKey = GetSeedLock();

            if (accessKey == null || accessKey.Length <= 0)
            {
                Log.ForContext<AuthCryptoHelper>().Error("Creating access key failed, Key must not be null or empty.");
                throw new System.Exception();
            }

            accessKey[accessKey.Length - 1] += 1;
            
            var keyCopri = KeyCopri;
            byte[] acccessKeyEncrypted;
            try
            {
                acccessKeyEncrypted = Cipher.Encrypt(
                    keyCopri,
                    accessKey);
            }
            catch (System.Exception exception)
            {
                Log.ForContext<AuthCryptoHelper>().Error("Encrypting access key failed. {Exception}", exception);
                throw;
            }

            Log.ForContext<AuthCryptoHelper>().Verbose($"Access key encrypted from {string.Join(",", accessKey)} to {string.Join(",", acccessKeyEncrypted)} using {string.Join(", ", keyCopri)}.");
            return acccessKeyEncrypted;
        }

        public byte[] KeyCopri { get; }
    }
}