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/*
* KDF defined in NIST SP 800-56a (Approved Alternative 1)
*
* (C) 2017 Ribose Inc. Written by Krzysztof Kwiatkowski.
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/sp800_56a.h>
#include <botan/scan_name.h>
#include <botan/exceptn.h>
namespace Botan {
namespace {
template<class AuxiliaryFunction_t>
size_t SP800_56A_kdf(
AuxiliaryFunction_t& auxfunc,
uint8_t key[], size_t key_len,
const uint8_t secret[], size_t secret_len,
const uint8_t label[], size_t label_len)
{
const uint64_t kRepsUpperBound = (1ULL << 32);
const size_t digest_len = auxfunc.output_length();
const size_t reps = key_len / digest_len + ((key_len % digest_len) ? 1 : 0);
if (reps >= kRepsUpperBound)
{
// See SP-800-56A, point 5.8.1
throw Invalid_Argument("SP800-56A KDF requested output too large");
}
uint32_t counter = 1;
secure_vector<uint8_t> result;
for(size_t i = 0; i < reps; i++)
{
auxfunc.update_be(counter++);
auxfunc.update(secret, secret_len);
auxfunc.update(label, label_len);
auxfunc.final(result);
const size_t offset = digest_len * i;
const size_t len = std::min(result.size(), key_len - offset);
copy_mem(&key[offset], result.data(), len);
}
return key_len;
}
}
size_t SP800_56A_Hash::kdf(uint8_t key[], size_t key_len,
const uint8_t secret[], size_t secret_len,
const uint8_t salt[], size_t salt_len,
const uint8_t label[], size_t label_len) const
{
/*
* TODO: should we reject a non-empty salt with an exception?
* Ignoring the salt seems quite dangerous to applications which
* don't expect it.
*/
BOTAN_UNUSED(salt, salt_len);
return SP800_56A_kdf(*m_hash, key, key_len, secret, secret_len, label, label_len);
}
SP800_56A_HMAC::SP800_56A_HMAC(MessageAuthenticationCode* mac) : m_mac(mac)
{
// TODO: we need a MessageAuthenticationCode::is_hmac
const SCAN_Name req(m_mac->name());
if(req.algo_name() != "HMAC")
{
throw Algorithm_Not_Found("Only HMAC can be used with KDF SP800-56A");
}
}
size_t SP800_56A_HMAC::kdf(uint8_t key[], size_t key_len,
const uint8_t secret[], size_t secret_len,
const uint8_t salt[], size_t salt_len,
const uint8_t label[], size_t label_len) const
{
/*
* SP 800-56A specifies if the salt is empty then a block of zeros
* equal to the hash's underlying block size are used. However this
* is equivalent to setting a zero-length key, so the same call
* works for either case.
*/
m_mac->set_key(salt, salt_len);
return SP800_56A_kdf(*m_mac, key, key_len, secret, secret_len, label, label_len);
}
}