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/*
* McEliece Integrated Encryption System
* (C) 2014,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/mceies.h>
#include <botan/aead.h>
#include <botan/mceliece.h>
#include <botan/mce_kem.h>
namespace Botan {
namespace {
secure_vector<byte> aead_key(const secure_vector<byte>& mk,
const AEAD_Mode& aead)
{
// Fold the key as required for the AEAD mode in use
if(aead.valid_keylength(mk.size()))
return mk;
secure_vector<byte> r(aead.key_spec().maximum_keylength());
for(size_t i = 0; i != mk.size(); ++i)
r[i % r.size()] ^= mk[i];
return r;
}
}
secure_vector<byte>
mceies_encrypt(const McEliece_PublicKey& pubkey,
const secure_vector<byte>& pt,
byte ad[], size_t ad_len,
RandomNumberGenerator& rng)
{
McEliece_KEM_Encryptor kem_op(pubkey);
const std::pair<secure_vector<byte>,secure_vector<byte>> mce_ciphertext__key = kem_op.encrypt(rng);
const secure_vector<byte>& mce_ciphertext = mce_ciphertext__key.first;
const secure_vector<byte>& mce_key = mce_ciphertext__key.second;
const size_t mce_code_bytes = (pubkey.get_code_length() + 7) / 8;
BOTAN_ASSERT(mce_ciphertext.size() == mce_code_bytes, "Unexpected size");
const std::string algo = "AES-256/OCB";
std::unique_ptr<AEAD_Mode> aead(get_aead(algo, ENCRYPTION));
if(!aead)
throw std::runtime_error("mce_encrypt unable to create AEAD instance '" + algo + "'");
const size_t nonce_len = aead->default_nonce_length();
aead->set_key(aead_key(mce_key, *aead));
aead->set_associated_data(ad, ad_len);
const secure_vector<byte> nonce = rng.random_vec(nonce_len);
secure_vector<byte> msg(mce_ciphertext.size() + nonce.size() + pt.size());
copy_mem(msg.data(), mce_ciphertext.data(), mce_ciphertext.size());
copy_mem(msg.data() + mce_ciphertext.size(), nonce.data(), nonce.size());
copy_mem(msg.data() + mce_ciphertext.size() + nonce.size(), pt.data(), pt.size());
aead->start(nonce);
aead->finish(msg, mce_ciphertext.size() + nonce.size());
return msg;
}
secure_vector<byte>
mceies_decrypt(const McEliece_PrivateKey& privkey,
const secure_vector<byte>& ct,
byte ad[], size_t ad_len)
{
try
{
McEliece_KEM_Decryptor kem_op(privkey);
const size_t mce_code_bytes = (privkey.get_code_length() + 7) / 8;
const std::string algo = "AES-256/OCB";
std::unique_ptr<AEAD_Mode> aead(get_aead(algo, DECRYPTION));
if(!aead)
throw std::runtime_error("Unable to create AEAD instance '" + algo + "'");
const size_t nonce_len = aead->default_nonce_length();
if(ct.size() < mce_code_bytes + nonce_len + aead->tag_size())
throw std::runtime_error("Input message too small to be valid");
const secure_vector<byte> mce_key = kem_op.decrypt(ct.data(), mce_code_bytes);
aead->set_key(aead_key(mce_key, *aead));
aead->set_associated_data(ad, ad_len);
secure_vector<byte> pt(ct.begin() + mce_code_bytes + nonce_len, ct.end());
aead->start(&ct[mce_code_bytes], nonce_len);
aead->finish(pt, 0);
return pt;
}
catch(std::exception& e)
{
throw std::runtime_error("mce_decrypt failed: " + std::string(e.what()));
}
}
}
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