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

        private static int DecryptNtlm(
            SafeDeleteContext securityContext,
            byte[] buffer,
            int offset,
            int count,
            bool isConfidential,
            out int newOffset,
            uint sequenceNumber)
        {
            const int ntlmSignatureLength = 16;
            // For the most part the arguments are verified in Decrypt().
            if (count < ntlmSignatureLength)
            {
                NetEventSource.Fail(null, "Argument 'count' out of range.");
                throw new ArgumentOutOfRangeException(nameof(count));
            }

            var securityBuffer = new SecurityBuffer[2];
            securityBuffer[0] = new SecurityBuffer(buffer, offset, ntlmSignatureLength, SecurityBufferType.SECBUFFER_TOKEN);
            securityBuffer[1] = new SecurityBuffer(buffer, offset + ntlmSignatureLength, count - ntlmSignatureLength, SecurityBufferType.SECBUFFER_DATA);

            int errorCode;
            SecurityBufferType realDataType = SecurityBufferType.SECBUFFER_DATA;

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

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

            if (securityBuffer[1].type != realDataType)
            {
                throw new InternalException();
            }

            newOffset = securityBuffer[1].offset;
            return securityBuffer[1].size;
        }
    }