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/*
* XMSS WOTS Parameters
* Descibes a signature method for XMSS Winternitz One Time Signatures,
* as defined in:
* [1] XMSS: Extended Hash-Based Signatures,
* Request for Comments: 8391
* Release: May 2018.
*
* (C) 2016,2017,2018 Matthias Gierlings
*
* Botan is released under the Simplified BSD License (see license.txt)
**/
#include <botan/xmss_wots.h>
#include <botan/internal/xmss_tools.h>
#include <botan/exceptn.h>
#include <cmath>
namespace Botan {
XMSS_WOTS_Parameters::ots_algorithm_t
XMSS_WOTS_Parameters::xmss_wots_id_from_string(const std::string& param_set)
{
if(param_set == "WOTSP-SHA2_256")
{ return WOTSP_SHA2_256; }
if(param_set == "WOTSP-SHA2_512")
{ return WOTSP_SHA2_512; }
if(param_set == "WOTSP-SHAKE_256")
{ return WOTSP_SHAKE_256; }
if(param_set == "WOTSP-SHAKE_512")
{ return WOTSP_SHAKE_512; }
throw Invalid_Argument("Unknown XMSS-WOTS algorithm param '" + param_set + "'");
}
XMSS_WOTS_Parameters::XMSS_WOTS_Parameters(const std::string& param_set)
: XMSS_WOTS_Parameters(xmss_wots_id_from_string(param_set))
{}
XMSS_WOTS_Parameters::XMSS_WOTS_Parameters(ots_algorithm_t oid)
: m_oid(oid)
{
switch(oid)
{
case WOTSP_SHA2_256:
m_element_size = 32;
m_w = 16;
m_len = 67;
m_name = "WOTSP-SHA2_256";
m_hash_name = "SHA-256";
m_strength = 256;
break;
case WOTSP_SHA2_512:
m_element_size = 64;
m_w = 16;
m_len = 131;
m_name = "WOTSP-SHA2_512";
m_hash_name = "SHA-512";
m_strength = 512;
break;
case WOTSP_SHAKE_256:
m_element_size = 32;
m_w = 16;
m_len = 67;
m_name = "WOTSP-SHAKE_256";
m_hash_name = "SHAKE-128(256)";
m_strength = 256;
break;
case WOTSP_SHAKE_512:
m_element_size = 64;
m_w = 16;
m_len = 131;
m_name = "WOTSP-SHAKE_512";
m_hash_name = "SHAKE-256(512)";
m_strength = 512;
break;
default:
throw Not_Implemented("Algorithm id does not match any known XMSS WOTS algorithm id.");
break;
}
m_lg_w = (m_w == 16) ? 4 : 2;
m_len_1 = static_cast<size_t>(std::ceil((8 * element_size()) / m_lg_w));
m_len_2 = static_cast<size_t>(
floor(log2(m_len_1 * (wots_parameter() - 1)) / m_lg_w) + 1);
BOTAN_ASSERT(m_len == m_len_1 + m_len_2, "Invalid XMSS WOTS parameter "
"\"len\" detedted.");
}
secure_vector<uint8_t>
XMSS_WOTS_Parameters::base_w(const secure_vector<uint8_t>& msg, size_t out_size) const
{
secure_vector<uint8_t> result;
size_t in = 0;
size_t total = 0;
size_t bits = 0;
for(size_t i = 0; i < out_size; i++)
{
if(bits == 0)
{
total = msg[in];
in++;
bits += 8;
}
bits -= m_lg_w;
result.push_back(static_cast<uint8_t>((total >> bits) & (m_w - 1)));
}
return result;
}
secure_vector<uint8_t>
XMSS_WOTS_Parameters::base_w(size_t value) const
{
value <<= (8 - ((m_len_2 * m_lg_w) % 8));
size_t len_2_bytes = static_cast<size_t>(
std::ceil(static_cast<float>(m_len_2 * m_lg_w) / 8.f));
secure_vector<uint8_t> result;
XMSS_Tools::concat(result, value, len_2_bytes);
return base_w(result, m_len_2);
}
void
XMSS_WOTS_Parameters::append_checksum(secure_vector<uint8_t>& data)
{
size_t csum = 0;
for(size_t i = 0; i < data.size(); i++)
{
csum += wots_parameter() - 1 - data[i];
}
secure_vector<uint8_t> csum_bytes = base_w(csum);
std::move(csum_bytes.begin(), csum_bytes.end(), std::back_inserter(data));
}
}