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/*
* EMSA1
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/emsa1.h>
#include <botan/exceptn.h>
#include <botan/pk_keys.h>
#include <botan/internal/padding.h>
namespace Botan {
namespace {
secure_vector<uint8_t> emsa1_encoding(const secure_vector<uint8_t>& msg,
size_t output_bits)
{
if(8*msg.size() <= output_bits)
return msg;
size_t shift = 8*msg.size() - output_bits;
size_t byte_shift = shift / 8, bit_shift = shift % 8;
secure_vector<uint8_t> digest(msg.size() - byte_shift);
for(size_t j = 0; j != msg.size() - byte_shift; ++j)
digest[j] = msg[j];
if(bit_shift)
{
uint8_t carry = 0;
for(size_t j = 0; j != digest.size(); ++j)
{
uint8_t temp = digest[j];
digest[j] = (temp >> bit_shift) | carry;
carry = (temp << (8 - bit_shift));
}
}
return digest;
}
}
std::string EMSA1::name() const
{
return "EMSA1(" + m_hash->name() + ")";
}
EMSA* EMSA1::clone()
{
return new EMSA1(m_hash->clone());
}
void EMSA1::update(const uint8_t input[], size_t length)
{
m_hash->update(input, length);
}
secure_vector<uint8_t> EMSA1::raw_data()
{
return m_hash->final();
}
secure_vector<uint8_t> EMSA1::encoding_of(const secure_vector<uint8_t>& msg,
size_t output_bits,
RandomNumberGenerator&)
{
if(msg.size() != hash_output_length())
throw Encoding_Error("EMSA1::encoding_of: Invalid size for input");
return emsa1_encoding(msg, output_bits);
}
bool EMSA1::verify(const secure_vector<uint8_t>& input,
const secure_vector<uint8_t>& raw,
size_t key_bits)
{
if(raw.size() != m_hash->output_length())
return false;
// Call emsa1_encoding to handle any required bit shifting
const secure_vector<uint8_t> our_coding = emsa1_encoding(raw, key_bits);
if(our_coding.size() < input.size())
return false;
const size_t offset = our_coding.size() - input.size(); // must be >= 0 per check above
// If our encoding is longer, all the bytes in it must be zero
for(size_t i = 0; i != offset; ++i)
if(our_coding[i] != 0)
return false;
return constant_time_compare(input.data(), &our_coding[offset], input.size());
}
AlgorithmIdentifier EMSA1::config_for_x509(const Private_Key& key,
const std::string& cert_hash_name) const
{
if(cert_hash_name != m_hash->name())
throw Invalid_Argument("Hash function from opts and hash_fn argument"
" need to be identical");
// check that the signature algorithm and the padding scheme fit
if(!sig_algo_and_pad_ok(key.algo_name(), "EMSA1"))
{
throw Invalid_Argument("Encoding scheme with canonical name EMSA1"
" not supported for signature algorithm " + key.algo_name());
}
const OID oid = OID::from_string(key.algo_name() + "/" + name());
const std::string algo_name = key.algo_name();
std::vector<uint8_t> parameters;
if(algo_name == "DSA" ||
algo_name == "ECDSA" ||
algo_name == "ECGDSA" ||
algo_name == "ECKCDSA" ||
algo_name == "GOST-34.10" ||
algo_name == "GOST-34.10-2012-256" ||
algo_name == "GOST-34.10-2012-512")
{
// for DSA, ECDSA, GOST parameters "SHALL" be empty
}
else
{
parameters = key.algorithm_identifier().get_parameters();
}
return AlgorithmIdentifier(oid, parameters);
}
}
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