TheAlgorithms/C-Sharp · error · ArgumentException

Not enough space in input array for padding

Error message

Not enough space in input array for padding

What it means

ISO 7816-4 AddPadding computes the space between inputOffset and the array end and throws ArgumentException when there is no byte left to write the mandatory 0x80 marker (code == 0) or the bounds check fails. The caller must pre-size the buffer to hold data plus at least one padding byte.

Solutions

1. Allocate the array with room for at least one extra byte beyond the data
2. Ensure 0 < inputData.Length - inputOffset before calling
3. If the buffer is exactly a multiple of the block size, add one extra block for padding

Example fix

// before
var buf = new byte[data.Length]; // full — no padding space
padding.AddPadding(buf, data.Length);
// after
var buf = new byte[data.Length + (blockSize - data.Length % blockSize)];
Array.Copy(data, buf, data.Length);
padding.AddPadding(buf, data.Length);

if (inputData == null || inputOffset < 0 || inputOffset >= inputData.Length)
    throw new ArgumentException("Need at least one free byte for ISO 7816-4 padding");

try { padding.AddPadding(buf, offset); }
catch (ArgumentException) { /* grow buffer to next block multiple and retry */ }

When it happens

Trigger: Calling AddPadding on a completely full buffer (inputOffset == inputData.Length), or with an offset that makes inputOffset + code exceed the array (offset overflow).

Common situations: Encrypting whole blocks of data without reserving an extra block for padding; miscounting buffer offsets when accumulating partial blocks in streaming code.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Not enough space in input array for padding
• Invalid padding length
• Padding block is corrupted
• Invalid padding
• Pad block corrupted

AI-assisted analysis of TheAlgorithms/C-Sharp@96e2905cab (2026-09-13). Data as JSON: /api/errors/f62af03c1e3f588b. Report an issue: GitHub.

Appendix: source

Thrown at Algorithms/Crypto/Paddings/Iso7816D4Padding.cs:48

{
    /// <summary>
    /// Adds padding to the input data according to the ISO 7816-4 standard.
    /// </summary>
    /// <param name="inputData">The input data array that needs padding.</param>
    /// <param name="inputOffset">The offset in the input data array where the padding should start.</param>
    /// <returns>The number of bytes added as padding.</returns>
    /// <exception cref="ArgumentException">
    /// Thrown when there is not enough space in the input array for padding or when the input offset is invalid.
    /// </exception>
    public int AddPadding(byte[] inputData, int inputOffset)
    {
        // Calculate the number of padding bytes based on the input data length and offset.
        var code = (byte)(inputData.Length - inputOffset);

        // Check if the padding bytes are valid and fit in the input array.
        if (code == 0 || inputOffset + code > inputData.Length)
        {
            throw new ArgumentException("Not enough space in input array for padding");
        }

        // Set the first padding byte to 80. This marks the start of padding in the ISO 7816-4 standard.
        inputData[inputOffset] = 80;
        inputOffset++;

        // Set the remaining padding bytes to 0.
        while (inputOffset < inputData.Length)
        {
            inputData[inputOffset] = 0;
            inputOffset++;
        }

        // Return the number of padding bytes.
        return code;
    }

    /// <summary>

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