1 /*
2 * Copyright 2024, 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 "SharedSecret.h"
18
19 #include <algorithm>
20 #include <cstring>
21 #include <mutex>
22 #include <vector>
23
24 #include <openssl/rand.h>
25
26 #include <KeyMintUtils.h>
27 #include <aidl/android/hardware/security/sharedsecret/BnSharedSecret.h>
28 #include <aidl/android/hardware/security/sharedsecret/SharedSecretParameters.h>
29 #include <android-base/logging.h>
30 #include <keymaster/android_keymaster_messages.h>
31 #include <keymaster/android_keymaster_utils.h>
32 #include <keymaster/km_openssl/ckdf.h>
33 #include <keymaster/km_openssl/hmac.h>
34
35 namespace aidl::android::hardware::security::sharedsecret {
36
getSharedSecretParameters(SharedSecretParameters * out_params)37 ::ndk::ScopedAStatus SoftSharedSecret::getSharedSecretParameters(
38 SharedSecretParameters* out_params) {
39 std::lock_guard lock(mutex_);
40 if (seed_.empty()) {
41 seed_.resize(32, 0);
42 }
43 out_params->seed = seed_;
44 if (nonce_.empty()) {
45 nonce_.resize(32, 0);
46 RAND_bytes(nonce_.data(), 32);
47 }
48 out_params->nonce = nonce_;
49 LOG(INFO) << "Presented shared secret parameters with seed size " << out_params->seed.size()
50 << " and nonce size " << out_params->nonce.size();
51 return ::ndk::ScopedAStatus::ok();
52 }
53
computeSharedSecret(const std::vector<SharedSecretParameters> & params,std::vector<uint8_t> * sharing_check)54 ::ndk::ScopedAStatus SoftSharedSecret::computeSharedSecret(
55 const std::vector<SharedSecretParameters>& params, std::vector<uint8_t>* sharing_check) {
56 std::lock_guard lock(mutex_);
57 LOG(INFO) << "Computing shared secret";
58 // Reimplemented based on SoftKeymasterEnforcement, which does not expose
59 // enough functionality to satisfy the GateKeeper interface
60 keymaster::KeymasterKeyBlob key_agreement_key;
61 if (key_agreement_key.Reset(32) == nullptr) {
62 LOG(ERROR) << "key agreement key memory allocation failed";
63 return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);
64 }
65 // Matching:
66 // - kFakeAgreementKey in system/keymaster/km_openssl/soft_keymaster_enforcement.cpp
67 // - Keys::kak in hardware/interfaces/security/keymint/aidl/default/ta/soft.rs
68 std::memset(key_agreement_key.writable_data(), 0, 32);
69 keymaster::KeymasterBlob label((uint8_t*)KEY_AGREEMENT_LABEL, strlen(KEY_AGREEMENT_LABEL));
70 if (label.data == nullptr) {
71 LOG(ERROR) << "label memory allocation failed";
72 return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);
73 }
74
75 static_assert(sizeof(keymaster_blob_t) == sizeof(keymaster::KeymasterBlob));
76
77 bool found_mine = false;
78 std::vector<keymaster::KeymasterBlob> context_blobs;
79 for (const auto& param : params) {
80 auto& seed_blob = context_blobs.emplace_back();
81 if (seed_blob.Reset(param.seed.size()) == nullptr) {
82 LOG(ERROR) << "seed memory allocation failed";
83 return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);
84 }
85 std::copy(param.seed.begin(), param.seed.end(), seed_blob.writable_data());
86 auto& nonce_blob = context_blobs.emplace_back();
87 if (nonce_blob.Reset(param.nonce.size()) == nullptr) {
88 LOG(ERROR) << "Nonce memory allocation failed";
89 return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);
90 }
91 std::copy(param.nonce.begin(), param.nonce.end(), nonce_blob.writable_data());
92 if (param.seed == seed_ && param.nonce == nonce_) {
93 found_mine = true;
94 }
95 }
96 if (!found_mine) {
97 LOG(ERROR) << "Did not receive my own shared secret parameter back";
98 return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_INVALID_ARGUMENT);
99 }
100 auto context_blobs_ptr = reinterpret_cast<keymaster_blob_t*>(context_blobs.data());
101 if (hmac_key_.Reset(32) == nullptr) {
102 LOG(ERROR) << "hmac key allocation failed";
103 return keymint::km_utils::kmError2ScopedAStatus(KM_ERROR_MEMORY_ALLOCATION_FAILED);
104 }
105 auto error = keymaster::ckdf(key_agreement_key, label, context_blobs_ptr, context_blobs.size(),
106 &hmac_key_);
107 if (error != KM_ERROR_OK) {
108 LOG(ERROR) << "CKDF failed";
109 return keymint::km_utils::kmError2ScopedAStatus(error);
110 }
111
112 keymaster::HmacSha256 hmac_impl;
113 if (!hmac_impl.Init(hmac_key_.key_material, hmac_key_.key_material_size)) {
114 LOG(ERROR) << "hmac initialization failed";
115 return ::ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
116 }
117 sharing_check->clear();
118 sharing_check->resize(32, 0);
119 if (!hmac_impl.Sign((const uint8_t*)KEY_CHECK_LABEL, strlen(KEY_CHECK_LABEL),
120 sharing_check->data(), sharing_check->size())) {
121 return ::ndk::ScopedAStatus::fromExceptionCode(EX_ILLEGAL_STATE);
122 }
123 return ::ndk::ScopedAStatus::ok();
124 }
125
HmacKey() const126 keymaster::KeymasterKeyBlob SoftSharedSecret::HmacKey() const {
127 std::lock_guard lock(mutex_);
128 return hmac_key_;
129 }
130
131 } // namespace aidl::android::hardware::security::sharedsecret
132