unpad static method

List<int> unpad(List<int> paddedData, int blockSize, { PaddingAlgorithm style = PaddingAlgorithm.pkcs7, })

Removes padding from the provided data.

This method removes padding from the input data, assuming it follows a specific padding style.

Parameters:

• paddedData: The padded data from which padding will be removed.
• blockSize: The block size used for padding.
• style: The padding style, which can be one of the PaddingAlgorithm values (default is pkcs7).

Returns:

• A new List<int> containing the input data with padding removed.

Throws:

• Exception for various scenarios, such as incorrect padding or zero-length input.

Implementation

static List<int> unpad(List<int> paddedData, int blockSize,
    {PaddingAlgorithm style = PaddingAlgorithm.pkcs7}) {
  final int paddedDataLen = paddedData.length;

  if (paddedDataLen == 0) {
    throw const ArgumentException('Zero-length input cannot be unpadded');
  }

  if (paddedDataLen % blockSize != 0) {
    throw const ArgumentException('Input data is not padded');
  }

  int paddingLen;

  if (style == PaddingAlgorithm.pkcs7 || style == PaddingAlgorithm.x923) {
    paddingLen = paddedData[paddedDataLen - 1];
    if (paddingLen < 1 || paddingLen > blockSize) {
      throw const ArgumentException('incorrect padding');
    }

    if (style == PaddingAlgorithm.pkcs7) {
      for (int i = 1; i <= paddingLen; i++) {
        if (paddedData[paddedDataLen - i] != paddingLen) {
          throw const ArgumentException('incorrect padding');
        }
      }
    } else {
      for (int i = 1; i < paddingLen; i++) {
        if (paddedData[paddedDataLen - i - 1] != 0) {
          throw const ArgumentException('incorrect padding');
        }
      }
    }
  } else {
    final int index = paddedData.lastIndexOf(128);
    if (index < 0) {
      throw const ArgumentException('incorrect padding');
    }
    paddingLen = paddedDataLen - index;
    if (paddingLen < 1 || paddingLen > blockSize) {
      throw const ArgumentException('incorrect padding');
    }
    for (int i = 1; i < paddingLen; i++) {
      if (paddedData[index + i] != 0) {
        throw const ArgumentException('incorrect padding');
      }
    }
  }
  return paddedData.sublist(0, paddedDataLen - paddingLen);
}