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/**
* XMSS Verification Operation
* Provides signature verification capabilities for Extended Hash-Based
* Signatures (XMSS).
*
* (C) 2016 Matthias Gierlings
*
* Botan is released under the Simplified BSD License (see license.txt)
**/
#include <botan/internal/xmss_verification_operation.h>
namespace Botan {
XMSS_Verification_Operation::XMSS_Verification_Operation(
const XMSS_PublicKey& public_key)
: XMSS_Common_Ops(public_key.xmss_oid()),
m_pub_key(public_key),
m_msg_buf(0)
{
}
secure_vector<byte>
XMSS_Verification_Operation::root_from_signature(const XMSS_Signature& sig,
const secure_vector<byte>& msg,
XMSS_Address& adrs,
const secure_vector<byte>& seed)
{
adrs.set_type(XMSS_Address::Type::OTS_Hash_Address);
adrs.set_ots_address(sig.unused_leaf_index());
XMSS_WOTS_PublicKey pub_key_ots(m_pub_key.wots_parameters().oid(),
msg,
sig.tree().ots_signature(),
adrs,
seed);
adrs.set_type(XMSS_Address::Type::LTree_Address);
adrs.set_ltree_address(sig.unused_leaf_index());
std::array<secure_vector<byte>, 2> node;
create_l_tree(node[0], pub_key_ots, adrs, seed);
adrs.set_type(XMSS_Address::Type::Hash_Tree_Address);
adrs.set_tree_index(sig.unused_leaf_index());
for(size_t k = 0; k < m_xmss_params.tree_height(); k++)
{
adrs.set_tree_height(k);
if(((sig.unused_leaf_index() / (1 << k)) & 0x01) == 0)
{
adrs.set_tree_index(adrs.get_tree_index() >> 1);
randomize_tree_hash(node[1],
node[0],
sig.tree().authentication_path()[k],
adrs,
seed);
}
else
{
adrs.set_tree_index((adrs.get_tree_index() - 1) >> 1);
randomize_tree_hash(node[1],
sig.tree().authentication_path()[k],
node[0],
adrs,
seed);
}
node[0] = node[1];
}
return node[0];
}
bool
XMSS_Verification_Operation::verify(const XMSS_Signature& sig,
const secure_vector<byte>& msg,
const XMSS_PublicKey& public_key)
{
XMSS_Address adrs;
secure_vector<byte> index_bytes;
XMSS_Tools::concat(index_bytes,
sig.unused_leaf_index(),
m_xmss_params.element_size());
secure_vector<byte> msg_digest =
m_hash.h_msg(sig.randomness(),
public_key.root(),
index_bytes,
msg);
secure_vector<byte> node = root_from_signature(sig,
msg_digest,
adrs,
public_key.public_seed());
return (node == public_key.root());
}
// FIXME: XMSS signature verification requires the "randomness" parameter out
// of the XMSS signature, which is part of the prefix that is hashed before
// msg. Since the signature is unknown till sign() is called all message
// content has to be buffered. For large messages this can be inconvenient or
// impossible.
// Possible solution: Change PK_Ops::Verification interface to take the
// signature as constructor argument, make sign a parameterless member call.
void XMSS_Verification_Operation::update(const byte msg[], size_t msg_len)
{
std::copy(msg, msg + msg_len, std::back_inserter(m_msg_buf));
}
bool XMSS_Verification_Operation::is_valid_signature(const byte sig[],
size_t sig_len)
{
try
{
XMSS_Signature signature(m_pub_key.xmss_parameters().oid(),
secure_vector<byte>(sig, sig + sig_len));
bool result = verify(signature, m_msg_buf, m_pub_key);
m_msg_buf.clear();
return result;
}
catch(Integrity_Failure& e)
{
m_msg_buf.clear();
return false;
}
}
}
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