Botan 3.9.0
Crypto and TLS for C&
Botan::OneAndZeros_Padding Class Referencefinal

#include <mode_pad.h>

Inheritance diagram for Botan::OneAndZeros_Padding:
Botan::BlockCipherModePaddingMethod

Public Member Functions

virtual void add_padding (std::span< uint8_t > buffer, size_t final_block_bytes, size_t block_size) const
void apply_padding (std::span< uint8_t > last_block, size_t final_block_bytes) const override
std::string name () const override
virtual size_t output_length (size_t input_length, size_t block_size) const
size_t remove_padding (std::span< const uint8_t > last_block) const override
size_t unpad (std::span< const uint8_t > last_block) const
bool valid_blocksize (size_t bs) const override

Static Public Member Functions

static std::unique_ptr< BlockCipherModePaddingMethodcreate (std::string_view algo_spec)

Detailed Description

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

Definition at line 134 of file mode_pad.h.

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
virtualinherited

Add padding bytes to buffer.

Parameters
bufferdata to pad, span must be large enough to hold the padding behind the final (partial) block
final_block_bytessize of the final block in bytes
block_sizesize of each block in bytes

Reimplemented in Botan::Null_Padding.

Definition at line 44 of file mode_pad.cpp.

44 {
46 BOTAN_ASSERT_NOMSG(last_byte_pos < BS);
47 BOTAN_ASSERT_NOMSG(buffer.size() % BS == 0);
48 BOTAN_ASSERT_NOMSG(buffer.size() >= BS);
49
50 auto poison = CT::scoped_poison(last_byte_pos, buffer);
51 apply_padding(buffer.last(BS), last_byte_pos);
52}
#define BOTAN_ASSERT_NOMSG(expr)
Definition assert.h:75
virtual bool valid_blocksize(size_t block_size) const =0
virtual void apply_padding(std::span< uint8_t > last_block, size_t padding_start_pos) const =0
constexpr auto scoped_poison(const Ts &... xs)
Definition ct_utils.h:220
constexpr void poison(const T *p, size_t n)
Definition ct_utils.h:54

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

◆ apply_padding()

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

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.

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 156 of file mode_pad.cpp.

156 {
157 /*
158 Padding format is
159 80
160 8000
161 800000
162 ...
163 */
164 for(size_t i = 0; i != last_block.size(); ++i) {
165 auto needs_80 = CT::Mask<uint8_t>(CT::Mask<size_t>::is_equal(i, padding_start_pos));
166 auto needs_00 = CT::Mask<uint8_t>(CT::Mask<size_t>::is_gt(i, padding_start_pos));
167 last_block[i] = needs_00.select(0x00, needs_80.select(0x80, last_block[i]));
168 }
169}
static constexpr Mask< T > is_equal(T x, T y)
Definition ct_utils.h:470
static constexpr Mask< T > is_gt(T x, T y)
Definition ct_utils.h:486

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

◆ 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_specblock cipher padding mode name

Get a block cipher padding method by name

Definition at line 20 of file mode_pad.cpp.

20 {
21 if(algo_spec == "NoPadding") {
22 return std::make_unique<Null_Padding>();
23 }
24
25 if(algo_spec == "PKCS7") {
26 return std::make_unique<PKCS7_Padding>();
27 }
28
29 if(algo_spec == "OneAndZeros") {
30 return std::make_unique<OneAndZeros_Padding>();
31 }
32
33 if(algo_spec == "X9.23") {
34 return std::make_unique<ANSI_X923_Padding>();
35 }
36
37 if(algo_spec == "ESP") {
38 return std::make_unique<ESP_Padding>();
39 }
40
41 return nullptr;
42}

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 142 of file mode_pad.h.

142{ return "OneAndZeros"; }

◆ output_length()

virtual size_t Botan::BlockCipherModePaddingMethod::output_length ( size_t input_length,
size_t block_size ) const
inlinevirtualinherited
Parameters
input_lengthnumber of bytes to be padded
block_sizesize 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.

66 {
67 return ((input_length + block_size) / block_size) * block_size;
68 }

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

◆ remove_padding()

size_t Botan::OneAndZeros_Padding::remove_padding ( std::span< const uint8_t > last_block) const
overridevirtual

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.

Implements Botan::BlockCipherModePaddingMethod.

Definition at line 174 of file mode_pad.cpp.

174 {
175 const size_t BS = input.size();
176 auto bad_input = CT::Mask<uint8_t>::cleared();
177 auto seen_0x80 = CT::Mask<uint8_t>::cleared();
178
179 size_t pad_pos = BS - 1;
180
181 for(size_t i = BS; i != 0; --i) {
182 const auto is_0x80 = CT::Mask<uint8_t>::is_equal(input[i - 1], 0x80);
183 const auto is_zero = CT::Mask<uint8_t>::is_zero(input[i - 1]);
184
185 seen_0x80 |= is_0x80;
186 pad_pos -= seen_0x80.if_not_set_return(1);
187 bad_input |= ~seen_0x80 & ~is_zero;
188 }
189 bad_input |= ~seen_0x80;
190
191 return CT::Mask<size_t>::expand(bad_input).select(BS, pad_pos);
192}
static constexpr Mask< T > expand(T v)
Definition ct_utils.h:420
static constexpr Mask< T > is_zero(T x)
Definition ct_utils.h:465
static constexpr Mask< T > cleared()
Definition ct_utils.h:415

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

◆ unpad()

size_t Botan::BlockCipherModePaddingMethod::unpad ( std::span< const uint8_t > last_block) const
inherited

Remove padding bytes from block

Parameters
last_blockthe 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.

54 {
55 if(!valid_blocksize(last_block.size())) {
56 return last_block.size();
57 }
58
59 auto poison = CT::scoped_poison(last_block);
60 return CT::driveby_unpoison(remove_padding(last_block));
61}
virtual size_t remove_padding(std::span< const uint8_t > last_block) const =0
decltype(auto) driveby_unpoison(T &&v)
Definition ct_utils.h:241

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

◆ valid_blocksize()

bool Botan::OneAndZeros_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 140 of file mode_pad.h.

140{ return (bs > 2); }

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