jstedfast/MailKit · error · ArgumentOutOfRangeException

inputOffset

Error message

inputOffset

What it means

DES.TransformBlock validates inputOffset with ArgumentOutOfRangeException: it must be >= 0 and <= inputBuffer.Length. A negative offset or an offset beyond the buffer is an indexing error MailKit catches before reading the block, instead of allowing an IndexOutOfRangeException or reading garbage.

Solutions

1. Clamp/verify inputOffset is within [0, inputBuffer.Length] before the call.
2. Fix the chunking loop so offset increments match the 8-byte block size.
3. Check that the buffer wasn't replaced/shrunk between computing the offset and calling TransformBlock.

Example fix

// before
des.TransformBlock(buf, off, 8, out, 0); // off may exceed buf.Length

// after
if (off >= 0 && off <= buf.Length - 8)
    des.TransformBlock(buf, off, 8, out, 0);

if (inputOffset >= 0 && inputOffset <= inputBuffer.Length)
    des.TransformBlock(inputBuffer, inputOffset, 8, outputBuffer, 0);

static bool ValidOffset(byte[] buf, int off) => off >= 0 && off <= buf.Length;

try {
    des.TransformBlock(buf, off, 8, outBuf, 0);
} catch (ArgumentOutOfRangeException ex) when (ex.ParamName == "inputOffset") {
    // recompute offset from buffer length before retrying
}

When it happens

Trigger: Calling TransformBlock with inputOffset < 0 or inputOffset > inputBuffer.Length, e.g. a miscomputed offset when processing a byte stream in 8-byte chunks.

Common situations: Manual chunking loops that advance the offset by the wrong stride; offsets captured before a buffer resize/reallocation; off-by-one from including a header length incorrectly.

Related errors

• inputCount
• outputOffset
• inputBuffer
• Can only transform 8 bytes at a time.
• outputBuffer

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/02c669c5aa8342f3. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Security/Ntlm/DES.cs:111

			public bool CanTransformMultipleBlocks {
				get { return false; }
			}

			public int InputBlockSize {
				get { return 8; }
			}

			public int OutputBlockSize {
				get { return 8; }
			}

			public int TransformBlock (byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
			{
				if (inputBuffer == null)
					throw new ArgumentNullException ("inputBuffer");

				if (inputOffset < 0 || inputOffset > inputBuffer.Length)
					throw new ArgumentOutOfRangeException ("inputOffset");

				if (inputCount < 0 || inputOffset > inputBuffer.Length - inputCount)
					throw new ArgumentOutOfRangeException ("inputCount");

				if (inputCount != 8)
					throw new ArgumentOutOfRangeException ("inputCount", "Can only transform 8 bytes at a time.");

				if (outputBuffer == null)
					throw new ArgumentNullException ("outputBuffer");

				if (outputOffset < 0 || outputOffset > outputBuffer.Length - 8)
					throw new ArgumentOutOfRangeException ("outputOffset");

				return engine.ProcessBlock (inputBuffer, inputOffset, outputBuffer, outputOffset);
			}

			public byte[] TransformFinalBlock (byte[] inputBuffer, int inputOffset, int inputCount)
			{

View on GitHub (pinned to 9d3859a785)