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 <keymaster/km_openssl/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 <keymaster/km_openssl/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 UniquePtr<NistCurveKeyExchange> key_exchange(new (std::nothrow) 64 NistCurveKeyExchange(key.get(), &error)); 65 if (!key_exchange.get()) error = KM_ERROR_MEMORY_ALLOCATION_FAILED; 66 if (error != KM_ERROR_OK) return nullptr; 67 (void)key.release(); 68 69 return key_exchange.release(); 70 } 71 72 keymaster_error_t NistCurveKeyExchange::ExtractPublicKey() { 73 const EC_GROUP* group = EC_KEY_get0_group(private_key_.get()); 74 size_t field_len_bits; 75 keymaster_error_t error = ec_get_group_size(group, &field_len_bits); 76 if (error != KM_ERROR_OK) return error; 77 78 shared_secret_len_ = (field_len_bits + 7) / 8; 79 public_key_len_ = 1 + 2 * shared_secret_len_; 80 public_key_.reset(new (std::nothrow) uint8_t[public_key_len_]); 81 if (!public_key_.get()) return KM_ERROR_MEMORY_ALLOCATION_FAILED; 82 if (EC_POINT_point2oct(group, EC_KEY_get0_public_key(private_key_.get()), 83 POINT_CONVERSION_UNCOMPRESSED, public_key_.get(), public_key_len_, 84 nullptr /* ctx */) != public_key_len_) { 85 return TranslateLastOpenSslError(); 86 } 87 return KM_ERROR_OK; 88 } 89 90 bool NistCurveKeyExchange::CalculateSharedKey(const Buffer& peer_public_value, 91 Buffer* out_result) const { 92 93 return CalculateSharedKey(peer_public_value.peek_read(), peer_public_value.available_read(), 94 out_result); 95 } 96 97 bool NistCurveKeyExchange::CalculateSharedKey(const uint8_t* peer_public_value, 98 size_t peer_public_value_len, 99 Buffer* out_result) const { 100 const EC_GROUP* group = EC_KEY_get0_group(private_key_.get()); 101 UniquePtr<EC_POINT, EC_POINT_Delete> point(EC_POINT_new(group)); 102 if (!point.get() || 103 !EC_POINT_oct2point(/* also test if point is on curve */ 104 group, point.get(), peer_public_value, peer_public_value_len, 105 nullptr /* ctx */) || 106 !EC_POINT_is_on_curve(group, point.get(), nullptr /* ctx */)) { 107 LOG_E("Can't convert peer public value to point: %d", TranslateLastOpenSslError()); 108 return false; 109 } 110 111 UniquePtr<uint8_t[]> result(new (std::nothrow) uint8_t[shared_secret_len_]); 112 if (!result.get()) return false; 113 if (ECDH_compute_key(result.get(), shared_secret_len_, point.get(), private_key_.get(), 114 nullptr /* kdf */) != static_cast<int>(shared_secret_len_)) { 115 LOG_E("Can't compute ECDH shared key: %d", TranslateLastOpenSslError()); 116 return false; 117 } 118 119 out_result->Reinitialize(result.get(), shared_secret_len_); 120 return true; 121 } 122 123 bool NistCurveKeyExchange::public_value(Buffer* public_value) const { 124 if (public_key_.get() != nullptr && public_key_len_ != 0) { 125 return public_value->Reinitialize(public_key_.get(), public_key_len_); 126 } 127 return false; 128 } 129 130 } // namespace keymaster 131