System.Net.Security.NegotiateStreamPal.Encrypt C# (CSharp) Method

        internal static int Encrypt(
            SafeDeleteContext securityContext,
            byte[] buffer,
            int offset,
            int count,
            bool isConfidential,
            bool isNtlm,
            ref byte[] output,
            uint sequenceNumber)
        {
            SecPkgContext_Sizes sizes = SSPIWrapper.QueryContextAttributes(
                GlobalSSPI.SSPIAuth,
                securityContext,
                Interop.SspiCli.ContextAttribute.SECPKG_ATTR_SIZES
                ) as SecPkgContext_Sizes;

            try
            {
                int maxCount = checked(Int32.MaxValue - 4 - sizes.cbBlockSize - sizes.cbSecurityTrailer);

                if (count > maxCount || count < 0)
                {
                    throw new ArgumentOutOfRangeException(nameof(count), SR.Format(SR.net_io_out_range, maxCount));
                }
            }
            catch (Exception e) when (!ExceptionCheck.IsFatal(e))
            {
                NetEventSource.Fail(null, "Arguments out of range.");
                throw;
            }

            int resultSize = count + sizes.cbSecurityTrailer + sizes.cbBlockSize;
            if (output == null || output.Length < resultSize + 4)
            {
                output = new byte[resultSize + 4];
            }

            // Make a copy of user data for in-place encryption.
            Buffer.BlockCopy(buffer, offset, output, 4 + sizes.cbSecurityTrailer, count);

            // Prepare buffers TOKEN(signature), DATA and Padding.
            var securityBuffer = new SecurityBuffer[3];
            securityBuffer[0] = new SecurityBuffer(output, 4, sizes.cbSecurityTrailer, SecurityBufferType.SECBUFFER_TOKEN);
            securityBuffer[1] = new SecurityBuffer(output, 4 + sizes.cbSecurityTrailer, count, SecurityBufferType.SECBUFFER_DATA);
            securityBuffer[2] = new SecurityBuffer(output, 4 + sizes.cbSecurityTrailer + count, sizes.cbBlockSize, SecurityBufferType.SECBUFFER_PADDING);

            int errorCode;
            if (isConfidential)
            {
                errorCode = SSPIWrapper.EncryptMessage(GlobalSSPI.SSPIAuth, securityContext, securityBuffer, sequenceNumber);
            }
            else
            {
                if (isNtlm)
                {
                    securityBuffer[1].type |= SecurityBufferType.SECBUFFER_READONLY;
                }

                errorCode = SSPIWrapper.MakeSignature(GlobalSSPI.SSPIAuth, securityContext, securityBuffer, 0);
            }

            if (errorCode != 0)
            {
                Exception e = new Win32Exception(errorCode);
                if (NetEventSource.IsEnabled) NetEventSource.Error(null, e);
                throw e;
            }

            // Compacting the result.
            resultSize = securityBuffer[0].size;
            bool forceCopy = false;
            if (resultSize != sizes.cbSecurityTrailer)
            {
                forceCopy = true;
                Buffer.BlockCopy(output, securityBuffer[1].offset, output, 4 + resultSize, securityBuffer[1].size);
            }

            resultSize += securityBuffer[1].size;
            if (securityBuffer[2].size != 0 && (forceCopy || resultSize != (count + sizes.cbSecurityTrailer)))
            {
                Buffer.BlockCopy(output, securityBuffer[2].offset, output, 4 + resultSize, securityBuffer[2].size);
            }

            resultSize += securityBuffer[2].size;
            unchecked
            {
                output[0] = (byte)((resultSize) & 0xFF);
                output[1] = (byte)(((resultSize) >> 8) & 0xFF);
                output[2] = (byte)(((resultSize) >> 16) & 0xFF);
                output[3] = (byte)(((resultSize) >> 24) & 0xFF);
            }

            return resultSize + 4;
        }