using System;

using System.Security.Cryptography;

namespace NETworkManager.Utilities;

public static class CryptoHelper

{

private static readonly int blockSize = 128;

/// <summary>

/// </summary>

/// <param name="decryptedBytes"></param>

/// <param name="password"></param>

/// <param name="keySize"></param>

/// <param name="iterations"></param>

/// <returns></returns>

public static byte[] Encrypt(byte[] decryptedBytes, string password, int keySize, int iterations)

{

ReadOnlySpan<byte> salt = RandomNumberGenerator.GetBytes(keySize / 8); // Generate salt based

ReadOnlySpan<byte>

iv = RandomNumberGenerator.GetBytes(blockSize / 8); // Generate iv, has to be the same as the block size

var key = Rfc2898DeriveBytes.Pbkdf2(password, salt, iterations, HashAlgorithmName.SHA512, keySize / 8);

using var aes = Aes.Create();

aes.Key = key;

var encryptedSize = aes.GetCiphertextLengthCbc(decryptedBytes.Length);

var cipher = new byte[salt.Length + iv.Length + encryptedSize];

Span<byte> cipherSpan = cipher;

salt.CopyTo(cipherSpan);

iv.CopyTo(cipherSpan[salt.Length..]);

var encrypted = aes.EncryptCbc(decryptedBytes, iv, cipherSpan[(salt.Length + iv.Length)..]);

return cipher;

}

/// <summary>

/// </summary>

/// <param name="encryptedBytesWithSaltAndIV"></param>

/// <param name="password"></param>

/// <param name="keySize"></param>

/// <param name="iterations"></param>

/// <returns></returns>

public static byte[] Decrypt(byte[] encryptedBytesWithSaltAndIV, string password, int keySize, int iterations)

{

ReadOnlySpan<byte> salt = encryptedBytesWithSaltAndIV.AsSpan(0, keySize / 8); // Take salt bytes

ReadOnlySpan<byte>

iv = encryptedBytesWithSaltAndIV.AsSpan(keySize / 8, blockSize / 8); // Skip salt bytes, take iv bytes

ReadOnlySpan<byte> cipher = encryptedBytesWithSaltAndIV.AsSpan(keySize / 8 + blockSize / 8);

var key = Rfc2898DeriveBytes.Pbkdf2(password, salt, iterations, HashAlgorithmName.SHA512, keySize / 8);

using var aes = Aes.Create();

aes.Key = key;

return aes.DecryptCbc(cipher, iv);

}

}