iTextSharp.text.pdf.crypto.StandardDecryption.Update C# (CSharp) Метод

        public byte[] Update(byte[] b, int off, int len)
        {
            if (aes) {
                if (initiated)
                    return cipher.Update(b, off, len);
                else {
                    int left = Math.Min(iv.Length - ivptr, len);
                    System.Array.Copy(b, off, iv, ivptr, left);
                    off += left;
                    len -= left;
                    ivptr += left;
                    if (ivptr == iv.Length) {
                        cipher = new AESCipher(false, key, iv);
                        initiated = true;
                        if (len > 0)
                            return cipher.Update(b, off, len);
                    }
                    return null;
                }
            }
            else {
                byte[] b2 = new byte[len];
                arcfour.EncryptARCFOUR(b, off, len, b2, 0);
                return b2;
            }
        }