iTextSharp.text.pdf.PdfEncryption.SetupUserKey C# (CSharp) Метод

        private void SetupUserKey()
        {
            if (revision == STANDARD_ENCRYPTION_128 || revision == AES_128) {
            md5.BlockUpdate(pad, 0, pad.Length);
            md5.BlockUpdate(documentID, 0, documentID.Length);
            byte[] digest = new byte[md5.GetDigestSize()];
            md5.DoFinal(digest, 0);
            md5.Reset();
            Array.Copy(digest, 0, userKey, 0, 16);
            for (int k = 16; k < 32; ++k)
                userKey[k] = 0;
            for (int i = 0; i < 20; ++i) {
                for (int j = 0; j < mkey.Length; ++j)
                    digest[j] = (byte)(mkey[j] ^ i);
                rc4.PrepareARCFOURKey(digest, 0, mkey.Length);
                rc4.EncryptARCFOUR(userKey, 0, 16);
            }
            }
            else {
            rc4.PrepareARCFOURKey(mkey);
            rc4.EncryptARCFOUR(pad, userKey);
            }
        }