Botan::OneAndZeros_Padding Class Reference

#include <mode_pad.h>

Inheritance diagram for Botan::OneAndZeros_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

Static Public Member Functions
static std::unique_ptr< BlockCipherModePaddingMethod >	create (std::string_view algo_spec)

Detailed Description

One And Zeros Padding (ISO/IEC 9797-1, padding method 2)

Definition at line 99 of file mode_pad.h.

Member Function Documentation

add_padding()

void Botan::OneAndZeros_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 181 of file mode_pad.cpp.

                                                                                                           {
   /*
   Padding format is
   80
   8000
   800000
   ...
   */
 
   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;
 
   for(size_t i = start_of_last_block; i != end_of_last_block; ++i) {
      auto needs_80 = CT::Mask<uint8_t>(CT::Mask<size_t>::is_equal(i, start_of_padding));
      auto needs_00 = CT::Mask<uint8_t>(CT::Mask<size_t>::is_gt(i, start_of_padding));
      buffer[i] = needs_00.select(0x00, needs_80.select(0x80, buffer[i]));
   }
 
   CT::unpoison(buffer.data(), buffer.size());
   CT::unpoison(last_byte_pos);
}

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

create()

std::unique_ptr< BlockCipherModePaddingMethod > Botan::BlockCipherModePaddingMethod::create ( std::string_view algo_spec )

staticinherited

Get a block cipher padding mode by name (eg "NoPadding" or "PKCS7")

Parameters

algo_spec

block cipher padding mode name

Get a block cipher padding method by name

Definition at line 19 of file mode_pad.cpp.

                                                                                                         {
   if(algo_spec == "NoPadding") {
      return std::make_unique<Null_Padding>();
   }
 
   if(algo_spec == "PKCS7") {
      return std::make_unique<PKCS7_Padding>();
   }
 
   if(algo_spec == "OneAndZeros") {
      return std::make_unique<OneAndZeros_Padding>();
   }
 
   if(algo_spec == "X9.23") {
      return std::make_unique<ANSI_X923_Padding>();
   }
 
   if(algo_spec == "ESP") {
      return std::make_unique<ESP_Padding>();
   }
 
   return nullptr;
}

Referenced by Botan::Cipher_Mode::create().

name()

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

inlineoverridevirtual

Returns

name of the mode

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 107 of file mode_pad.h.

{ return "OneAndZeros"; }

unpad()

size_t Botan::OneAndZeros_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 219 of file mode_pad.cpp.

                                                                                  {
   if(!valid_blocksize(input_length)) {
      return input_length;
   }
 
   CT::poison(input, input_length);
 
   auto bad_input = CT::Mask<uint8_t>::cleared();
   auto seen_0x80 = CT::Mask<uint8_t>::cleared();
 
   size_t pad_pos = input_length - 1;
   size_t i = input_length;
 
   while(i) {
      const auto is_0x80 = CT::Mask<uint8_t>::is_equal(input[i - 1], 0x80);
      const auto is_zero = CT::Mask<uint8_t>::is_zero(input[i - 1]);
 
      seen_0x80 |= is_0x80;
      pad_pos -= seen_0x80.if_not_set_return(1);
      bad_input |= ~seen_0x80 & ~is_zero;
      i--;
   }
   bad_input |= ~seen_0x80;
 
   CT::unpoison(input, input_length);
 
   return CT::Mask<size_t>::expand(bad_input).select_and_unpoison(input_length, pad_pos);
}

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

valid_blocksize()

bool Botan::OneAndZeros_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 105 of file mode_pad.h.

{ return (bs > 2); }

Referenced by unpad().

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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