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
NistCurveKeyExchange(EC_KEY * private_key,keymaster_error_t * error)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 */
GenerateKeyExchange(keymaster_ec_curve_t curve)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
ExtractPublicKey()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
CalculateSharedKey(const Buffer & peer_public_value,Buffer * out_result) const88 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
CalculateSharedKey(const uint8_t * peer_public_value,size_t peer_public_value_len,Buffer * out_result) const95 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
public_value(Buffer * public_value) const120 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