1 // Copyright 2017 Google Inc.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 ///////////////////////////////////////////////////////////////////////////////
16
17 #include "tink/subtle/aes_cmac_boringssl.h"
18
19 #include <cstdint>
20 #include <memory>
21 #include <string>
22 #include <utility>
23
24 #include "absl/memory/memory.h"
25 #include "absl/status/status.h"
26 #include "openssl/cmac.h"
27 #include "openssl/evp.h"
28 #include "tink/internal/aes_util.h"
29 #include "tink/internal/ssl_unique_ptr.h"
30 #include "tink/internal/util.h"
31 #include "tink/subtle/subtle_util.h"
32 #include "tink/util/errors.h"
33 #include "tink/util/status.h"
34 #include "tink/util/statusor.h"
35
36 namespace crypto {
37 namespace tink {
38 namespace subtle {
39 // CMAC key sizes in bytes.
40 // The small key size is used only to check RFC 4493's test vectors due to
41 // the attack described in
42 // https://www.math.uwaterloo.ca/~ajmeneze/publications/tightness.pdf. We
43 // check this restriction in AesCmacManager.
44 static constexpr size_t kSmallKeySize = 16;
45 static constexpr size_t kBigKeySize = 32;
46 static constexpr size_t kMaxTagSize = 16;
47
48 // static
New(util::SecretData key,uint32_t tag_size)49 util::StatusOr<std::unique_ptr<Mac>> AesCmacBoringSsl::New(util::SecretData key,
50 uint32_t tag_size) {
51 auto status = internal::CheckFipsCompatibility<AesCmacBoringSsl>();
52 if (!status.ok()) return status;
53
54 if (key.size() != kSmallKeySize && key.size() != kBigKeySize) {
55 return ToStatusF(absl::StatusCode::kInvalidArgument,
56 "Invalid key size: expected %d or %d, found %d",
57 kSmallKeySize, kBigKeySize, key.size());
58 }
59 if (tag_size > kMaxTagSize) {
60 return ToStatusF(absl::StatusCode::kInvalidArgument,
61 "Invalid tag size: expected lower than %d, found %d",
62 kMaxTagSize, tag_size);
63 }
64 return {absl::WrapUnique(new AesCmacBoringSsl(std::move(key), tag_size))};
65 }
66
ComputeMac(absl::string_view data) const67 util::StatusOr<std::string> AesCmacBoringSsl::ComputeMac(
68 absl::string_view data) const {
69 // BoringSSL expects a non-null pointer for data,
70 // regardless of whether the size is 0.
71 data = internal::EnsureStringNonNull(data);
72
73 std::string result;
74 ResizeStringUninitialized(&result, kMaxTagSize);
75 internal::SslUniquePtr<CMAC_CTX> context(CMAC_CTX_new());
76 util::StatusOr<const EVP_CIPHER*> cipher =
77 internal::GetAesCbcCipherForKeySize(key_.size());
78 if (!cipher.ok()) {
79 return cipher.status();
80 }
81 size_t len = 0;
82 const uint8_t* key_ptr = reinterpret_cast<const uint8_t*>(&key_[0]);
83 const uint8_t* data_ptr = reinterpret_cast<const uint8_t*>(data.data());
84 uint8_t* result_ptr = reinterpret_cast<uint8_t*>(&result[0]);
85 if (CMAC_Init(context.get(), key_ptr, key_.size(), *cipher, nullptr) <= 0 ||
86 CMAC_Update(context.get(), data_ptr, data.size()) <= 0 ||
87 CMAC_Final(context.get(), result_ptr, &len) == 0) {
88 return util::Status(absl::StatusCode::kInternal, "Failed to compute CMAC");
89 }
90
91 result.resize(tag_size_);
92 return result;
93 }
94
VerifyMac(absl::string_view mac,absl::string_view data) const95 util::Status AesCmacBoringSsl::VerifyMac(absl::string_view mac,
96 absl::string_view data) const {
97 if (mac.size() != tag_size_) {
98 return ToStatusF(absl::StatusCode::kInvalidArgument,
99 "Incorrect tag size: expected %d, found %d", tag_size_,
100 mac.size());
101 }
102 util::StatusOr<std::string> computed_mac = ComputeMac(data);
103 if (!computed_mac.ok()) return computed_mac.status();
104 if (CRYPTO_memcmp(computed_mac->data(), mac.data(), tag_size_) != 0) {
105 return util::Status(absl::StatusCode::kInvalidArgument,
106 "CMAC verification failed");
107 }
108 return util::OkStatus();
109 }
110
111 } // namespace subtle
112 } // namespace tink
113 } // namespace crypto
114