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/*
* Copyright 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "ecies_kem.h"
#include "nist_curve_key_exchange.h"
#include "openssl_err.h"
namespace keymaster {
EciesKem::EciesKem(const AuthorizationSet& kem_description, keymaster_error_t* error) {
AuthorizationSet authorizations(kem_description);
if (!authorizations.GetTagValue(TAG_EC_CURVE, &curve_)) {
LOG_E("%s", "EciesKem: no curve specified");
*error = KM_ERROR_INVALID_ARGUMENT;
return;
}
switch (curve_) {
case KM_EC_CURVE_P_224:
case KM_EC_CURVE_P_256:
case KM_EC_CURVE_P_384:
case KM_EC_CURVE_P_521:
break;
default:
LOG_E("EciesKem: curve %d is unsupported", curve_);
*error = KM_ERROR_UNSUPPORTED_EC_CURVE;
return;
}
keymaster_kdf_t kdf;
if (!authorizations.GetTagValue(TAG_KDF, &kdf)) {
LOG_E("EciesKem: No KDF specified", 0);
*error = KM_ERROR_UNSUPPORTED_KDF;
return;
}
switch (kdf) {
case KM_KDF_RFC5869_SHA256:
kdf_.reset(new Rfc5869Sha256Kdf());
break;
default:
LOG_E("Kdf %d is unsupported", kdf);
*error = KM_ERROR_UNSUPPORTED_KDF;
return;
}
if (!kdf_.get()) {
*error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
return;
}
if (!authorizations.GetTagValue(TAG_KEY_SIZE, &key_bytes_to_generate_)) {
LOG_E("%s", "EciesKem: no key length specified");
*error = KM_ERROR_UNSUPPORTED_KEY_SIZE;
return;
}
single_hash_mode_ = authorizations.GetTagValue(TAG_ECIES_SINGLE_HASH_MODE);
*error = KM_ERROR_OK;
}
bool EciesKem::Encrypt(const Buffer& peer_public_value, Buffer* output_clear_key,
Buffer* output_encrypted_key) {
return Encrypt(peer_public_value.peek_read(), peer_public_value.available_read(),
output_clear_key, output_encrypted_key);
}
// http://www.shoup.net/iso/std6.pdf, section 10.2.3.
bool EciesKem::Encrypt(const uint8_t* peer_public_value, size_t peer_public_value_len,
Buffer* output_clear_key, Buffer* output_encrypted_key) {
key_exchange_.reset(NistCurveKeyExchange::GenerateKeyExchange(curve_));
if (!key_exchange_.get()) {
return false;
}
Buffer shared_secret;
if (!key_exchange_->CalculateSharedKey(peer_public_value, peer_public_value_len,
&shared_secret)) {
LOG_E("EciesKem: ECDH failed, can't obtain shared secret", 0);
return false;
}
if (!key_exchange_->public_value(output_encrypted_key)) {
LOG_E("EciesKem: Can't obtain public value", 0);
return false;
}
Buffer z;
if (single_hash_mode_) {
// z is empty.
} else {
// z = C0
z.Reinitialize(output_encrypted_key->peek_read(), output_encrypted_key->available_read());
}
Buffer actual_secret(z.available_read() + shared_secret.available_read());
actual_secret.write(z.peek_read(), z.available_read());
actual_secret.write(shared_secret.peek_read(), shared_secret.available_read());
if (!kdf_->Init(actual_secret.peek_read(), actual_secret.available_read(), nullptr /* salt */,
0 /* salt_len */)) {
LOG_E("EciesKem: KDF failed, can't derived keys", 0);
return false;
}
output_clear_key->Reinitialize(key_bytes_to_generate_);
if (!kdf_->GenerateKey(nullptr /* info */, 0 /* info length */, output_clear_key->peek_write(),
key_bytes_to_generate_)) {
LOG_E("EciesKem: KDF failed, can't derived keys", 0);
return false;
}
output_clear_key->advance_write(key_bytes_to_generate_);
return true;
}
bool EciesKem::Decrypt(EC_KEY* private_key, const Buffer& encrypted_key, Buffer* output_key) {
return Decrypt(private_key, encrypted_key.peek_read(), encrypted_key.available_read(),
output_key);
}
// http://www.shoup.net/iso/std6.pdf, section 10.2.4.
bool EciesKem::Decrypt(EC_KEY* private_key, const uint8_t* encrypted_key, size_t encrypted_key_len,
Buffer* output_key) {
keymaster_error_t error;
key_exchange_.reset(new NistCurveKeyExchange(private_key, &error));
if (!key_exchange_.get() || error != KM_ERROR_OK) {
return false;
}
Buffer shared_secret;
if (!key_exchange_->CalculateSharedKey(encrypted_key, encrypted_key_len, &shared_secret)) {
LOG_E("EciesKem: ECDH failed, can't obtain shared secret", 0);
return false;
}
Buffer public_value;
if (!key_exchange_->public_value(&public_value)) {
LOG_E("%s", "EciesKem: Can't obtain public value");
return false;
}
Buffer z;
if (single_hash_mode_) {
// z is empty.
} else {
// z = C0
z.Reinitialize(public_value.peek_read(), public_value.available_read());
}
Buffer actual_secret(z.available_read() + shared_secret.available_read());
actual_secret.write(z.peek_read(), z.available_read());
actual_secret.write(shared_secret.peek_read(), shared_secret.available_read());
if (!kdf_->Init(actual_secret.peek_read(), actual_secret.available_read(), nullptr /* salt */,
0 /* salt_len */)) {
LOG_E("%s", "EciesKem: KDF failed, can't derived keys");
return false;
}
output_key->Reinitialize(key_bytes_to_generate_);
if (!kdf_->GenerateKey(nullptr /* info */, 0 /* info_len */, output_key->peek_write(),
key_bytes_to_generate_)) {
LOG_E("%s", "EciesKem: KDF failed, can't derived keys");
return false;
}
output_key->advance_write(key_bytes_to_generate_);
return true;
}
} // namespace keymaster
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