Botan 2.19.1
Crypto and TLS for C&
Public Member Functions | List of all members
Botan::ANSI_X923_Padding Class Referencefinal

#include <mode_pad.h>

Inheritance diagram for Botan::ANSI_X923_Padding:
Botan::BlockCipherModePaddingMethod

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

ANSI X9.23 Padding

Definition at line 86 of file mode_pad.h.

Member Function Documentation

◆ add_padding()

void Botan::ANSI_X923_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
bufferdata to pad
final_block_bytessize of the final block in bytes
block_sizesize of each block in bytes

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 116 of file mode_pad.cpp.

119 {
120 /*
121 Padding format is
122 01
123 0002
124 000003
125 ...
126 */
127 BOTAN_DEBUG_ASSERT(last_byte_pos < BS);
128
129 const uint8_t padding_len = static_cast<uint8_t>(BS - last_byte_pos);
130
131 buffer.resize(buffer.size() + padding_len);
132
133 CT::poison(&last_byte_pos, 1);
134 CT::poison(buffer.data(), buffer.size());
135
136 BOTAN_DEBUG_ASSERT(buffer.size() % BS == 0);
137 BOTAN_DEBUG_ASSERT(buffer.size() >= BS);
138
139 const size_t start_of_last_block = buffer.size() - BS;
140 const size_t end_of_zero_padding = buffer.size() - 1;
141 const size_t start_of_padding = buffer.size() - padding_len;
142
143 for(size_t i = start_of_last_block; i != end_of_zero_padding; ++i)
144 {
145 auto needs_padding = CT::Mask<uint8_t>(CT::Mask<size_t>::is_gte(i, start_of_padding));
146 buffer[i] = needs_padding.select(0, buffer[i]);
147 }
148
149 buffer[buffer.size()-1] = padding_len;
150 CT::unpoison(buffer.data(), buffer.size());
151 CT::unpoison(last_byte_pos);
152 }
#define BOTAN_DEBUG_ASSERT(expr)
Definition: assert.h:123
static Mask< T > is_gte(T x, T y)
Definition: ct_utils.h:181
void poison(const T *p, size_t n)
Definition: ct_utils.h:48
void unpoison(const T *p, size_t n)
Definition: ct_utils.h:59

References BOTAN_DEBUG_ASSERT, Botan::CT::poison(), and Botan::CT::unpoison().

◆ name()

std::string Botan::ANSI_X923_Padding::name ( ) const
inlineoverridevirtual
Returns
name of the mode

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 97 of file mode_pad.h.

97{ return "X9.23"; }

◆ unpad()

size_t Botan::ANSI_X923_Padding::unpad ( const uint8_t  block[],
size_t  len 
) const
overridevirtual

Remove padding bytes from block

Parameters
blockthe last block
lenthe 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 157 of file mode_pad.cpp.

158 {
159 if(!valid_blocksize(input_length))
160 return input_length;
161
162 CT::poison(input, input_length);
163
164 const size_t last_byte = input[input_length-1];
165
166 auto bad_input = CT::Mask<size_t>::is_gt(last_byte, input_length);
167
168 const size_t pad_pos = input_length - last_byte;
169
170 for(size_t i = 0; i != input_length - 1; ++i)
171 {
172 // Ignore values that are not part of the padding
173 const auto in_range = CT::Mask<size_t>::is_gte(i, pad_pos);
174 const auto pad_is_nonzero = CT::Mask<size_t>::expand(input[i]);
175 bad_input |= pad_is_nonzero & in_range;
176 }
177
178 CT::unpoison(input, input_length);
179
180 return bad_input.select_and_unpoison(input_length, pad_pos);
181 }
bool valid_blocksize(size_t bs) const override
Definition: mode_pad.h:95
static Mask< T > is_gt(T x, T y)
Definition: ct_utils.h:165
static Mask< T > expand(T v)
Definition: ct_utils.h:123

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

◆ valid_blocksize()

bool Botan::ANSI_X923_Padding::valid_blocksize ( size_t  block_size) const
inlineoverridevirtual
Parameters
block_sizeof the cipher
Returns
valid block size for this padding mode

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 95 of file mode_pad.h.

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

Referenced by unpad().


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