Botan::BlockCipherModePaddingMethod Class Reference

#include <mode_pad.h>

Inheritance diagram for Botan::BlockCipherModePaddingMethod:

Public Member Functions
virtual void	add_padding (std::span< uint8_t > buffer, size_t final_block_bytes, size_t block_size) const
virtual std::string	name () const =0
virtual size_t	output_length (size_t input_length, size_t block_size) const
size_t	unpad (std::span< const uint8_t > last_block) const
virtual bool	valid_blocksize (size_t block_size) const =0
virtual	~BlockCipherModePaddingMethod ()=default

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

Protected Member Functions
virtual void	apply_padding (std::span< uint8_t > last_block, size_t padding_start_pos) const =0
virtual size_t	remove_padding (std::span< const uint8_t > last_block) const =0

Detailed Description

Block Cipher Mode Padding Method This class is pretty limited, it cannot deal well with randomized padding methods, or any padding method that wants to add more than one block. For instance, it should be possible to define cipher text stealing mode as simply a padding mode for CBC, which happens to consume the last two block (and requires use of the block cipher).

Definition at line 30 of file mode_pad.h.

Constructor & Destructor Documentation

~BlockCipherModePaddingMethod()

virtual Botan::BlockCipherModePaddingMethod::~BlockCipherModePaddingMethod ( )

virtualdefault

virtual destructor

Member Function Documentation

add_padding()

void Botan::BlockCipherModePaddingMethod::add_padding ( std::span< uint8_t > buffer, size_t final_block_bytes, size_t block_size ) const

virtual

Add padding bytes to buffer.

Parameters

buffer	data to pad, span must be large enough to hold the padding behind the final (partial) block
final_block_bytes	size of the final block in bytes
block_size	size of each block in bytes

Reimplemented in Botan::Null_Padding.

Definition at line 44 of file mode_pad.cpp.

                                                                                                             {
   BOTAN_ASSERT_NOMSG(valid_blocksize(BS));
   BOTAN_ASSERT_NOMSG(last_byte_pos < BS);
   BOTAN_ASSERT_NOMSG(buffer.size() % BS == 0);
   BOTAN_ASSERT_NOMSG(buffer.size() >= BS);
 
   auto poison = CT::scoped_poison(last_byte_pos, buffer);
   apply_padding(buffer.last(BS), last_byte_pos);
}

References apply_padding(), BOTAN_ASSERT_NOMSG, Botan::CT::scoped_poison(), and valid_blocksize().

apply_padding()

virtual void Botan::BlockCipherModePaddingMethod::apply_padding ( std::span< uint8_t > last_block, size_t padding_start_pos ) const

protectedpure virtual

Applies the concrete padding to the last_block assuming the padding bytes should start at padding_start_pos within the last block.

Concrete implementations of this function must ensure not to leak padding_start_pos via side channels. Both the bytes of last_block and padding_start_pos are passed in with CT::poison applied.

Implemented in Botan::ANSI_X923_Padding, Botan::ESP_Padding, Botan::OneAndZeros_Padding, and Botan::PKCS7_Padding.

Referenced by add_padding().

create()

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

static

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 20 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()

virtual std::string Botan::BlockCipherModePaddingMethod::name ( ) const

pure virtual

Returns

name of the mode

Implemented in Botan::ANSI_X923_Padding, Botan::ESP_Padding, Botan::Null_Padding, Botan::OneAndZeros_Padding, and Botan::PKCS7_Padding.

output_length()

virtual size_t Botan::BlockCipherModePaddingMethod::output_length ( size_t input_length, size_t block_size ) const

inlinevirtual

Parameters

input_length	number of bytes to be padded
block_size	size of each block in bytes

Returns

the total number of output bytes (including the padding)

Reimplemented in Botan::Null_Padding.

Definition at line 66 of file mode_pad.h.

                                                                                 {
         return ((input_length + block_size) / block_size) * block_size;
      }

Referenced by Botan::CBC_Encryption::output_length().

remove_padding()

virtual size_t Botan::BlockCipherModePaddingMethod::remove_padding ( std::span< const uint8_t > last_block ) const

protectedpure virtual

Removes the padding from last_block and returns the number of data bytes. If the padding is invalid, this returns the byte length of last_block.

Concrete implementations of this function must ensure not to leak the size or validity of the padding via side channels. The bytes of last_block are passed in with CT::poison applied to them.

Implemented in Botan::ANSI_X923_Padding, Botan::ESP_Padding, Botan::Null_Padding, Botan::OneAndZeros_Padding, and Botan::PKCS7_Padding.

Referenced by unpad().

unpad()

size_t Botan::BlockCipherModePaddingMethod::unpad

(

std::span< const uint8_t >

last_block

)

const

Remove padding bytes from block

Parameters

last_block

the last block containing the padding

Returns

number of data bytes, or if the padding is invalid returns the byte length of last_block (i.e. the block size)

Definition at line 54 of file mode_pad.cpp.

                                                                                  {
   if(!valid_blocksize(last_block.size())) {
      return last_block.size();
   }
 
   auto poison = CT::scoped_poison(last_block);
   return CT::driveby_unpoison(remove_padding(last_block));
}

References Botan::CT::driveby_unpoison(), remove_padding(), Botan::CT::scoped_poison(), and valid_blocksize().

valid_blocksize()

virtual bool Botan::BlockCipherModePaddingMethod::valid_blocksize ( size_t block_size ) const

pure virtual

Parameters

block_size

of the cipher

Returns

valid block size for this padding mode

Implemented in Botan::ANSI_X923_Padding, Botan::ESP_Padding, Botan::Null_Padding, Botan::OneAndZeros_Padding, and Botan::PKCS7_Padding.

Referenced by add_padding(), and unpad().

---

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