sharee.bike-App/LockIt.BusinessLogic/Services/BluetoothLock/Crypto/AuthCryptoHelper.cs

using Serilog;
using ShareeBike.Model.Device;

namespace ShareeBike.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; }
	}
}