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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/rng.h>
#include <botan/mceliece.h>
#include <botan/pubkey.h>
namespace Botan {
namespace {
secure_vector<uint8_t> aead_key(const secure_vector<uint8_t>& 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<uint8_t> r(aead.key_spec().maximum_keylength());
BOTAN_ASSERT_NOMSG(r.size() > 0);
for(size_t i = 0; i != mk.size(); ++i)
r[i % r.size()] ^= mk[i];
return r;
}
}
secure_vector<uint8_t>
mceies_encrypt(const McEliece_PublicKey& pubkey,
const uint8_t pt[], size_t pt_len,
const uint8_t ad[], size_t ad_len,
RandomNumberGenerator& rng,
const std::string& algo)
{
PK_KEM_Encryptor kem_op(pubkey, rng, "KDF1(SHA-512)");
secure_vector<uint8_t> mce_ciphertext, mce_key;
kem_op.encrypt(mce_ciphertext, mce_key, 64, rng);
const size_t mce_code_bytes = (pubkey.get_code_length() + 7) / 8;
BOTAN_ASSERT(mce_ciphertext.size() == mce_code_bytes, "Unexpected size");
std::unique_ptr<AEAD_Mode> aead = AEAD_Mode::create_or_throw(algo, ENCRYPTION);
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<uint8_t> nonce = rng.random_vec(nonce_len);
secure_vector<uint8_t> msg(mce_ciphertext.size() + nonce.size() + pt_len);
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, pt_len);
aead->start(nonce);
aead->finish(msg, mce_ciphertext.size() + nonce.size());
return msg;
}
secure_vector<uint8_t>
mceies_decrypt(const McEliece_PrivateKey& privkey,
const uint8_t ct[], size_t ct_len,
const uint8_t ad[], size_t ad_len,
const std::string& algo)
{
try
{
Null_RNG null_rng;
PK_KEM_Decryptor kem_op(privkey, null_rng, "KDF1(SHA-512)");
const size_t mce_code_bytes = (privkey.get_code_length() + 7) / 8;
std::unique_ptr<AEAD_Mode> aead = AEAD_Mode::create_or_throw(algo, DECRYPTION);
const size_t nonce_len = aead->default_nonce_length();
if(ct_len < mce_code_bytes + nonce_len + aead->tag_size())
throw Decoding_Error("Input message too small to be valid");
const secure_vector<uint8_t> mce_key = kem_op.decrypt(ct, mce_code_bytes, 64);
aead->set_key(aead_key(mce_key, *aead));
aead->set_associated_data(ad, ad_len);
secure_vector<uint8_t> pt(ct + mce_code_bytes + nonce_len, ct + ct_len);
aead->start(&ct[mce_code_bytes], nonce_len);
aead->finish(pt, 0);
return pt;
}
catch(Invalid_Authentication_Tag&)
{
throw;
}
catch(std::exception& e)
{
throw Decoding_Error("mce_decrypt failed: " + std::string(e.what()));
}
}
}
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