1 // Copyright 2021 Google LLC
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 #include "fcp/secagg/shared/aes_key.h"
16
17 #include <string>
18
19 #include "gmock/gmock.h"
20 #include "gtest/gtest.h"
21 #include "absl/strings/str_cat.h"
22 #include "fcp/secagg/shared/math.h"
23 #include "fcp/secagg/shared/shamir_secret_sharing.h"
24
25 namespace fcp {
26 namespace secagg {
27 namespace {
28
29 using ::testing::Eq;
30
31 // For testing purposes, make an AesKey out of a string.
AesKeyFromString(const std::string & key)32 AesKey AesKeyFromString(const std::string& key) {
33 return AesKey(reinterpret_cast<const uint8_t*>(key.c_str()),
34 static_cast<int>(key.size()));
35 }
36
37 // Suppose the randomly chosen key can be expressed in bit_length <= 128 bits.
38 // Java did not express the key in 128 bits, but rather will have used
39 // (bit_length + 1) bits. The extra bit is the highest-order bit, and is a sign
40 // bit, guaranteed to be 0. The next highest-order bit is guaranteed to be 1.
JavaStyleKey(int bit_length)41 std::string JavaStyleKey(int bit_length) {
42 EXPECT_TRUE(0 < bit_length && bit_length <= 128);
43 std::string key = "16 byte test key";
44 int byte_with_sign_bit = (127 - bit_length) / 8;
45 int pos_of_sign_bit = (127 - bit_length) % 8;
46 if (bit_length == 128) {
47 pos_of_sign_bit = 7;
48 key = absl::StrCat("\0", key);
49 } else {
50 key.erase(0, byte_with_sign_bit);
51 }
52 // Make sure the high-order bit is the sign bit 0, and the next highest-order
53 // bit is 1.
54 key[0] = static_cast<char>(127 >> pos_of_sign_bit);
55 if (pos_of_sign_bit == 7) {
56 key[1] = static_cast<char>(255);
57 }
58 return key;
59 }
60
TEST(AesKeyTest,CreateFromSharesHandles32BKeys)61 TEST(AesKeyTest, CreateFromSharesHandles32BKeys) {
62 AesKey original_key = AesKeyFromString("32 byte AES key for testing only");
63 ShamirSecretSharing shamir;
64 auto shares = shamir.Share(5, 7, original_key);
65 auto key_or_error = AesKey::CreateFromShares(shares, 5);
66 EXPECT_THAT(key_or_error.ok(), Eq(true));
67 EXPECT_THAT(key_or_error.value(), Eq(original_key));
68 }
69
TEST(AesKeyTest,CreateFromSharesHandlesShortKeys)70 TEST(AesKeyTest, CreateFromSharesHandlesShortKeys) {
71 ShamirSecretSharing shamir;
72 for (int i = 1; i <= 128; ++i) {
73 std::string original_key_string = JavaStyleKey(i);
74 AesKey original_key = AesKeyFromString(original_key_string);
75 std::string key_string_for_sharing;
76 if (original_key_string.size() < 16) {
77 key_string_for_sharing =
78 absl::StrCat(std::string(16 - original_key_string.size(), '\0'),
79 original_key_string);
80 } else if (original_key_string.size() == 17) {
81 key_string_for_sharing = original_key_string.substr(1);
82 } else {
83 key_string_for_sharing = original_key_string;
84 }
85 auto shares = shamir.Share(5, 7, AesKeyFromString(key_string_for_sharing));
86 auto key_or_error = AesKey::CreateFromShares(shares, 5);
87 EXPECT_THAT(key_or_error.ok(), Eq(true));
88 EXPECT_THAT(key_or_error.value(), Eq(original_key))
89 << i << " bit key fails";
90 }
91 }
92
93 } // namespace
94 } // namespace secagg
95 } // namespace fcp
96