public static void DecryptFile(string infile, string outfile, string key, int rounds = 20, string encoding = "iso-8859-1")
{
if (!File.Exists(infile))
{
throw new ArgumentException("Input file does not exist.");
}
byte[] buff = new byte[buffsize];
byte[] iv = new byte[10];
int read;
using (var input = File.OpenRead(infile))
{
if ((read = input.Read(iv, 0, 10)) != 10)
{
throw new Exception("Invalid input file.");
}
using (var output = File.OpenWrite(outfile))
{
List <byte> keybytes = new List <byte>();
keybytes.AddRange(Encoding.GetEncoding(encoding).GetBytes(key.Substring(0, Math.Min(key.Length, 246))));
keybytes.AddRange(iv);
var rc4 = new RC4(keybytes.ToArray(), rounds);
while ((read = input.Read(buff, 0, buffsize)) > 0)
{
output.Write(rc4.CryptBytes(buff, read), 0, read);
}
}
}
}