Botan::ESP_Padding Class Reference

#include <mode_pad.h>

Inheritance diagram for Botan::ESP_Padding:

Public Member Functions
void	add_padding (secure_vector< uint8_t > &buffer, size_t final_block_bytes, size_t block_size) const override
std::string	name () const override
size_t	unpad (const uint8_t[], size_t) const override
bool	valid_blocksize (size_t bs) const override

Detailed Description

ESP Padding (RFC 4304)

Definition at line 120 of file mode_pad.h.

Member Function Documentation

add_padding()

void Botan::ESP_Padding::add_padding ( secure_vector< uint8_t > &  buffer, size_t  final_block_bytes, size_t  block_size  ) const

overridevirtual

Add padding bytes to buffer.

Parameters

buffer	data to pad
final_block_bytes	size of the final block in bytes
block_size	size of each block in bytes

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 261 of file mode_pad.cpp.

References BOTAN_DEBUG_ASSERT, Botan::CT::Mask< T >::is_gte(), Botan::CT::poison(), Botan::CT::Mask< T >::select(), and Botan::CT::unpoison().

   {
   /*
   Padding format is
   01
   0102
   010203
   ...
   */
   BOTAN_DEBUG_ASSERT(last_byte_pos < BS);

   const uint8_t padding_len = static_cast<uint8_t>(BS - last_byte_pos);

   buffer.resize(buffer.size() + padding_len);

   CT::poison(&last_byte_pos, 1);
   CT::poison(buffer.data(), buffer.size());

   BOTAN_DEBUG_ASSERT(buffer.size() % BS == 0);
   BOTAN_DEBUG_ASSERT(buffer.size() >= BS);

   const size_t start_of_last_block = buffer.size() - BS;
   const size_t end_of_last_block = buffer.size();
   const size_t start_of_padding = buffer.size() - padding_len;

   uint8_t pad_ctr = 0x01;

   for(size_t i = start_of_last_block; i != end_of_last_block; ++i)
      {
      auto needs_padding = CT::Mask<uint8_t>(CT::Mask<size_t>::is_gte(i, start_of_padding));
      buffer[i] = needs_padding.select(pad_ctr, buffer[i]);
      pad_ctr = needs_padding.select(pad_ctr + 1, pad_ctr);
      }

   CT::unpoison(buffer.data(), buffer.size());
   CT::unpoison(last_byte_pos);
   }

name()

std::string Botan::ESP_Padding::name ( ) const

inlineoverridevirtual

Returns

name of the mode

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 131 of file mode_pad.h.

{ return "ESP"; }

unpad()

size_t Botan::ESP_Padding::unpad ( const uint8_t  block[], size_t  len  ) const

overridevirtual

Remove padding bytes from block

Parameters

block	the last block
len	the size of the block in bytes

Returns

number of data bytes, or if the padding is invalid returns len

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 304 of file mode_pad.cpp.

References Botan::CT::Mask< T >::is_equal(), Botan::CT::Mask< T >::is_gt(), Botan::CT::Mask< T >::is_zero(), Botan::CT::poison(), Botan::CT::unpoison(), and valid_blocksize().

   {
   if(!valid_blocksize(input_length))
      return input_length;

   CT::poison(input, input_length);

   const uint8_t input_length_8 = static_cast<uint8_t>(input_length);
   const uint8_t last_byte = input[input_length-1];

   auto bad_input = CT::Mask<uint8_t>::is_zero(last_byte) |
      CT::Mask<uint8_t>::is_gt(last_byte, input_length_8);

   const uint8_t pad_pos = input_length_8 - last_byte;
   size_t i = input_length_8 - 1;
   while(i)
      {
      const auto in_range = CT::Mask<size_t>::is_gt(i, pad_pos);
      const auto incrementing = CT::Mask<uint8_t>::is_equal(input[i-1], input[i]-1);

      bad_input |= CT::Mask<uint8_t>(in_range) & ~incrementing;
      --i;
      }

   CT::unpoison(input, input_length);
   return bad_input.select_and_unpoison(input_length_8, pad_pos);
   }

valid_blocksize()

bool Botan::ESP_Padding::valid_blocksize ( size_t  block_size ) const

inlineoverridevirtual

Parameters

block_size

of the cipher

Returns

valid block size for this padding mode

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 129 of file mode_pad.h.

Referenced by unpad().

{ return (bs > 2 && bs < 256); }

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The documentation for this class was generated from the following files:

• src/lib/modes/mode_pad/mode_pad.h
• src/lib/modes/mode_pad/mode_pad.cpp