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/*
* ISO-9796-2 - Digital signature schemes giving message recovery schemes 2 and 3
* (C) 2016 Tobias Niemann, Hackmanit GmbH
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/iso9796.h>
#include <botan/mgf1.h>
#include <botan/internal/bit_ops.h>
#include <botan/hash_id.h>
namespace Botan {
namespace {
secure_vector<byte> iso9796_encoding(const secure_vector<byte>& msg,
size_t output_bits, std::unique_ptr<HashFunction>& hash, size_t SALT_SIZE, bool implicit, RandomNumberGenerator& rng)
{
const size_t output_length = (output_bits + 7) / 8;
//set trailer length
size_t tLength = 1;
if(!implicit)
{
tLength = 2;
}
const size_t HASH_SIZE = hash->output_length();
if(output_length <= HASH_SIZE + SALT_SIZE + tLength)
{
throw Encoding_Error("ISO9796-2::encoding_of: Output length is too small");
}
//calculate message capacity
const size_t capacity = output_length
- HASH_SIZE - SALT_SIZE - tLength - 1;
//msg1 is the recoverable and msg2 the unrecoverable message part.
secure_vector<byte> msg1;
secure_vector<byte> msg2;
if(msg.size() > capacity)
{
msg1 = secure_vector<byte> (msg.begin(), msg.begin() + capacity);
msg2 = secure_vector<byte> (msg.begin() + capacity, msg.end());
hash->update(msg2);
}
else
{
msg1 = msg;
}
msg2 = hash->final();
//compute H(C||msg1 ||H(msg2)||S)
uint64_t msgLength = msg1.size();
secure_vector<byte> salt = rng.random_vec(SALT_SIZE);
hash->update_be(msgLength * 8);
hash->update(msg1);
hash->update(msg2);
hash->update(salt);
secure_vector<byte> H = hash->final();
secure_vector<byte> EM(output_length);
//compute message offset.
size_t offset = output_length - HASH_SIZE - SALT_SIZE - tLength
- msgLength - 1;
//insert message border (0x01), msg1 and salt into the output buffer
EM[offset] = 0x01;
buffer_insert(EM, offset + 1, msg1);
buffer_insert(EM, offset + 1 + msgLength, salt);
//apply mask
mgf1_mask(*hash, H.data(), HASH_SIZE, EM.data(),
output_length - HASH_SIZE - tLength);
buffer_insert(EM, output_length - HASH_SIZE - tLength, H);
//set implicit/ISO trailer
if(!implicit)
{
byte hash_id = ieee1363_hash_id(hash->name());
if(!hash_id)
{
throw Encoding_Error("ISO9796-2::encoding_of: no hash identifier for " + hash->name());
}
EM[output_length - 1] = 0xCC;
EM[output_length - 2] = hash_id;
}
else
{
EM[output_length - 1] = 0xBC;
}
//clear the leftmost bit (confer bouncy castle)
EM[0] &= 0x7F;
return EM;
}
bool iso9796_verification(const secure_vector<byte>& const_coded,
const secure_vector<byte>& raw, size_t key_bits, std::unique_ptr<HashFunction>& hash, size_t SALT_SIZE)
{
const size_t HASH_SIZE = hash->output_length();
const size_t KEY_BYTES = (key_bits + 7) / 8;
if(const_coded.size() != KEY_BYTES)
{
return false;
}
//get trailer length
size_t tLength;
if(const_coded[const_coded.size() - 1] == 0xBC)
{
tLength = 1;
}
else
{
byte hash_id = ieee1363_hash_id(hash->name());
if((!const_coded[const_coded.size() - 2]) || (const_coded[const_coded.size() - 2] != hash_id) ||
(const_coded[const_coded.size() - 1] != 0xCC))
{
return false; //in case of wrong ISO trailer.
}
tLength = 2;
}
secure_vector<byte> coded = const_coded;
//remove mask
byte* DB = coded.data();
const size_t DB_size = coded.size() - HASH_SIZE - tLength;
const byte* H = &coded[DB_size];
mgf1_mask(*hash, H, HASH_SIZE, DB, DB_size);
//clear the leftmost bit (confer bouncy castle)
DB[0] &= 0x7F;
//recover msg1 and salt
size_t msg1_offset = 0;
for(size_t j = 0; j != DB_size; ++j)
{
if(DB[j] == 0x01)
{
msg1_offset = j + 1;
break;
}
}
if(msg1_offset == 0)
{
return false;
}
secure_vector<byte> msg1(coded.begin() + msg1_offset,
coded.end() - tLength - HASH_SIZE - SALT_SIZE);
secure_vector<byte> salt(coded.begin() + msg1_offset + msg1.size(),
coded.end() - tLength - HASH_SIZE);
//compute H2(C||msg1||H(msg2)||S*). * indicates a recovered value
const size_t capacity = (key_bits - 2 + 7) / 8 - HASH_SIZE
- SALT_SIZE - tLength - 1;
secure_vector<byte> msg1raw;
secure_vector<byte> msg2;
if(raw.size() > capacity)
{
msg1raw = secure_vector<byte> (raw.begin(), raw.begin() + capacity);
msg2 = secure_vector<byte> (raw.begin() + capacity, raw.end());
hash->update(msg2);
}
else
{
msg1raw = raw;
}
msg2 = hash->final();
uint64_t msg1rawLength = msg1raw.size();
hash->update_be(msg1rawLength * 8);
hash->update(msg1raw);
hash->update(msg2);
hash->update(salt);
secure_vector<byte> H3 = hash->final();
//compute H3(C*||msg1*||H(msg2)||S*) * indicates a recovered value
uint64_t msgLength = msg1.size();
hash->update_be(msgLength * 8);
hash->update(msg1);
hash->update(msg2);
hash->update(salt);
secure_vector<byte> H2 = hash->final();
//check if H3 == H2
return same_mem(H3.data(), H2.data(), HASH_SIZE);
}
}
/*
* ISO-9796-2 signature scheme 2
* DS 2 is probabilistic
*/
void ISO_9796_DS2::update(const byte input[], size_t length)
{
//need to buffer message completely, before digest
m_msg_buffer.insert(m_msg_buffer.end(), input, input+length);
}
/*
* Return the raw (unencoded) data
*/
secure_vector<byte> ISO_9796_DS2::raw_data()
{
secure_vector<byte> retbuffer = m_msg_buffer;
m_msg_buffer.clear();
return retbuffer;
}
/*
* ISO-9796-2 scheme 2 encode operation
*/
secure_vector<byte> ISO_9796_DS2::encoding_of(const secure_vector<byte>& msg,
size_t output_bits, RandomNumberGenerator& rng)
{
return iso9796_encoding(msg, output_bits, m_hash, m_SALT_SIZE, m_implicit, rng);
}
/*
* ISO-9796-2 scheme 2 verify operation
*/
bool ISO_9796_DS2::verify(const secure_vector<byte>& const_coded,
const secure_vector<byte>& raw, size_t key_bits)
{
return iso9796_verification(const_coded,raw,key_bits,m_hash,m_SALT_SIZE);
}
/*
* ISO-9796-2 signature scheme 3
* DS 3 is deterministic and equals DS2 without salt
*/
void ISO_9796_DS3::update(const byte input[], size_t length)
{
//need to buffer message completely, before digest
m_msg_buffer.insert(m_msg_buffer.end(), input, input+length);
}
/*
* Return the raw (unencoded) data
*/
secure_vector<byte> ISO_9796_DS3::raw_data()
{
secure_vector<byte> retbuffer = m_msg_buffer;
m_msg_buffer.clear();
return retbuffer;
}
/*
* ISO-9796-2 scheme 3 encode operation
*/
secure_vector<byte> ISO_9796_DS3::encoding_of(const secure_vector<byte>& msg,
size_t output_bits, RandomNumberGenerator& rng)
{
return iso9796_encoding(msg, output_bits, m_hash, 0, m_implicit, rng);
}
/*
* ISO-9796-2 scheme 3 verify operation
*/
bool ISO_9796_DS3::verify(const secure_vector<byte>& const_coded,
const secure_vector<byte>& raw, size_t key_bits)
{
return iso9796_verification(const_coded, raw, key_bits, m_hash, 0);
}
}
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