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      1 /*
      2  * Copyright 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include "nist_curve_key_exchange.h"
     18 
     19 #include <openssl/ec.h>
     20 #include <openssl/ecdh.h>
     21 #include <openssl/err.h>
     22 #include <openssl/evp.h>
     23 
     24 #include "openssl_err.h"
     25 
     26 namespace keymaster {
     27 
     28 NistCurveKeyExchange::NistCurveKeyExchange(EC_KEY* private_key, keymaster_error_t* error)
     29     : private_key_(private_key) {
     30     if (!private_key_.get() || !EC_KEY_check_key(private_key_.get())) {
     31         *error = KM_ERROR_INVALID_ARGUMENT;
     32         return;
     33     }
     34     *error = ExtractPublicKey();
     35 }
     36 
     37 /* static */
     38 NistCurveKeyExchange* NistCurveKeyExchange::GenerateKeyExchange(keymaster_ec_curve_t curve) {
     39     int curve_name;
     40     switch (curve) {
     41     case KM_EC_CURVE_P_224:
     42         curve_name = NID_secp224r1;
     43         break;
     44     case KM_EC_CURVE_P_256:
     45         curve_name = NID_X9_62_prime256v1;
     46         break;
     47     case KM_EC_CURVE_P_384:
     48         curve_name = NID_secp384r1;
     49         break;
     50     case KM_EC_CURVE_P_521:
     51         curve_name = NID_secp521r1;
     52         break;
     53     default:
     54         LOG_E("Not a NIST curve: %d", curve);
     55         return nullptr;
     56     }
     57 
     58     UniquePtr<EC_KEY, EC_KEY_Delete> key(EC_KEY_new_by_curve_name(curve_name));
     59     if (!key.get() || !EC_KEY_generate_key(key.get())) {
     60         return nullptr;
     61     }
     62     keymaster_error_t error;
     63     NistCurveKeyExchange* key_exchange = new NistCurveKeyExchange(key.release(), &error);
     64     if (error != KM_ERROR_OK) {
     65         return nullptr;
     66     }
     67     return key_exchange;
     68 }
     69 
     70 keymaster_error_t NistCurveKeyExchange::ExtractPublicKey() {
     71     const EC_GROUP* group = EC_KEY_get0_group(private_key_.get());
     72     size_t field_len_bits;
     73     keymaster_error_t error = ec_get_group_size(group, &field_len_bits);
     74     if (error != KM_ERROR_OK)
     75         return error;
     76 
     77     shared_secret_len_ = (field_len_bits + 7) / 8;
     78     public_key_len_ = 1 + 2 * shared_secret_len_;
     79     public_key_.reset(new uint8_t[public_key_len_]);
     80     if (EC_POINT_point2oct(group, EC_KEY_get0_public_key(private_key_.get()),
     81                            POINT_CONVERSION_UNCOMPRESSED, public_key_.get(), public_key_len_,
     82                            nullptr /* ctx */) != public_key_len_) {
     83         return TranslateLastOpenSslError();
     84     }
     85     return KM_ERROR_OK;
     86 }
     87 
     88 bool NistCurveKeyExchange::CalculateSharedKey(const Buffer& peer_public_value,
     89                                               Buffer* out_result) const {
     90 
     91     return CalculateSharedKey(peer_public_value.peek_read(), peer_public_value.available_read(),
     92                               out_result);
     93 }
     94 
     95 bool NistCurveKeyExchange::CalculateSharedKey(const uint8_t* peer_public_value,
     96                                               size_t peer_public_value_len,
     97                                               Buffer* out_result) const {
     98     const EC_GROUP* group = EC_KEY_get0_group(private_key_.get());
     99     UniquePtr<EC_POINT, EC_POINT_Delete> point(EC_POINT_new(group));
    100     if (!point.get() ||
    101         !EC_POINT_oct2point(/* also test if point is on curve */
    102                             group, point.get(), peer_public_value, peer_public_value_len,
    103                             nullptr /* ctx */) ||
    104         !EC_POINT_is_on_curve(group, point.get(), nullptr /* ctx */)) {
    105         LOG_E("Can't convert peer public value to point: %d", TranslateLastOpenSslError());
    106         return false;
    107     }
    108 
    109     UniquePtr<uint8_t[]> result(new uint8_t[shared_secret_len_]);
    110     if (ECDH_compute_key(result.get(), shared_secret_len_, point.get(), private_key_.get(),
    111                          nullptr /* kdf */) != static_cast<int>(shared_secret_len_)) {
    112         LOG_E("Can't compute ECDH shared key: %d", TranslateLastOpenSslError());
    113         return false;
    114     }
    115 
    116     out_result->Reinitialize(result.get(), shared_secret_len_);
    117     return true;
    118 }
    119 
    120 bool NistCurveKeyExchange::public_value(Buffer* public_value) const {
    121     if (public_key_.get() != nullptr && public_key_len_ != 0) {
    122         return public_value->Reinitialize(public_key_.get(), public_key_len_);
    123     }
    124     return false;
    125 }
    126 
    127 }  // namespace keymaster