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      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 <gtest/gtest.h>
     20 #include <openssl/evp.h>
     21 
     22 #include <hardware/keymaster_defs.h>
     23 #include <keymaster/android_keymaster_utils.h>
     24 
     25 #include "android_keymaster_test_utils.h"
     26 
     27 using std::string;
     28 
     29 namespace keymaster {
     30 namespace test {
     31 
     32 StdoutLogger logger;
     33 
     34 static const keymaster_ec_curve_t kEcCurves[] = {KM_EC_CURVE_P_224, KM_EC_CURVE_P_256,
     35                                                  KM_EC_CURVE_P_384, KM_EC_CURVE_P_521};
     36 
     37 /**
     38  * SharedKey just tests that the basic key exchange identity holds: that both
     39  * parties end up with the same key.
     40  */
     41 TEST(NistCurveKeyExchange, SharedKey) {
     42     for (auto& curve : kEcCurves) {
     43         AuthorizationSet kex_description(
     44             AuthorizationSetBuilder().Authorization(TAG_EC_CURVE, curve));
     45         for (size_t j = 0; j < 5; j++) {
     46             NistCurveKeyExchange* alice_keyex = NistCurveKeyExchange::GenerateKeyExchange(curve);
     47             NistCurveKeyExchange* bob_keyex = NistCurveKeyExchange::GenerateKeyExchange(curve);
     48 
     49             ASSERT_TRUE(alice_keyex != nullptr);
     50             ASSERT_TRUE(bob_keyex != nullptr);
     51 
     52             Buffer alice_public_value;
     53             ASSERT_TRUE(alice_keyex->public_value(&alice_public_value));
     54             Buffer bob_public_value;
     55             ASSERT_TRUE(bob_keyex->public_value(&bob_public_value));
     56 
     57             Buffer alice_shared, bob_shared;
     58             ASSERT_TRUE(alice_keyex->CalculateSharedKey(bob_public_value, &alice_shared));
     59             ASSERT_TRUE(bob_keyex->CalculateSharedKey(alice_public_value, &bob_shared));
     60             EXPECT_EQ(alice_shared.available_read(), bob_shared.available_read());
     61             EXPECT_EQ(0, memcmp(alice_shared.peek_read(), bob_shared.peek_read(),
     62                                 alice_shared.available_read()));
     63         }
     64     }
     65 }
     66 
     67 /*
     68  * This test tries a key agreement with a false public key (i.e. with
     69  * a point not on the curve.)
     70  * The expected result of such a protocol should be that the
     71  * key agreement fails and returns an error.
     72 */
     73 static const char* kInvalidPublicKeys[] = {
     74     "04"  // uncompressed public key
     75     "deadbeef7f56584c5cc632ca65640db91b6bacce3a4df6b42ce7cc838833d287"
     76     "db71e509e3fd9b060ddb20ba5c51dcc5948d46fbf640dfe0441782cab85fa4ac",
     77 };
     78 
     79 TEST(NistCurveKeyExchange, InvalidPublicKey) {
     80     for (auto& curve : kEcCurves) {
     81         AuthorizationSet kex_description(
     82             AuthorizationSetBuilder().Authorization(TAG_EC_CURVE, curve));
     83         KeyExchange* key_exchange = NistCurveKeyExchange::GenerateKeyExchange(curve);
     84         ASSERT_TRUE(key_exchange != nullptr);
     85 
     86         string peer_public_key = hex2str(kInvalidPublicKeys[0]);
     87         Buffer computed_shared_secret;
     88         ASSERT_FALSE(key_exchange->CalculateSharedKey(
     89             reinterpret_cast<const uint8_t*>(peer_public_key.data()), peer_public_key.size(),
     90             &computed_shared_secret));
     91     }
     92 }
     93 
     94 /**
     95  * Test that key exchange fails when peer public key is the point at infinity.
     96  */
     97 TEST(NistCurveKeyExchange, TestInfinity) {
     98     for (auto& curve : kEcCurves) {
     99         /* Obtain the point at infinity */
    100         EC_GROUP* group = ec_get_group(curve);
    101         EC_POINT* point_at_infinity = EC_POINT_new(group);
    102         EC_POINT_set_to_infinity(group, point_at_infinity);
    103         EXPECT_EQ(1, EC_POINT_is_on_curve(group, point_at_infinity, nullptr));
    104         size_t field_len_in_bits;
    105         ec_get_group_size(group, &field_len_in_bits);
    106         size_t field_len = (field_len_in_bits + 7) / 8;
    107         size_t public_key_len = (field_len * 2) + 1;
    108         uint8_t* public_key = new uint8_t[public_key_len];
    109         public_key_len = EC_POINT_point2oct(group, point_at_infinity, POINT_CONVERSION_UNCOMPRESSED,
    110                                             public_key, public_key_len, nullptr /* ctx */);
    111 
    112         /* Perform the key exchange */
    113         AuthorizationSet kex_description(
    114             AuthorizationSetBuilder().Authorization(TAG_EC_CURVE, curve));
    115         NistCurveKeyExchange* key_exchange = NistCurveKeyExchange::GenerateKeyExchange(curve);
    116         ASSERT_TRUE(key_exchange != nullptr);
    117         Buffer computed_shared_secret;
    118         /* It should fail */
    119         ASSERT_FALSE(key_exchange->CalculateSharedKey(reinterpret_cast<const uint8_t*>(public_key),
    120                                                       public_key_len, &computed_shared_secret));
    121 
    122         /* Explicitly test that ECDH_compute_key fails when the public key is the point at infinity
    123          */
    124         UniquePtr<uint8_t[]> result(new uint8_t[field_len]);
    125         EXPECT_EQ(-1 /* error */, ECDH_compute_key(result.get(), field_len, point_at_infinity,
    126                                                    key_exchange->private_key(), nullptr /* kdf */));
    127     }
    128 }
    129 
    130 /* Test vectors for P-256, downloaded from NIST. */
    131 struct NistCurveTest {
    132     const keymaster_ec_curve_t curve;
    133     const char* peer_public_key;
    134     const char* my_private_key;
    135     const char* shared_secret;
    136 };
    137 
    138 static const NistCurveTest kNistCurveTests[] = {
    139     {
    140         KM_EC_CURVE_P_256,
    141         "04"  // uncompressed public key
    142         "700c48f77f56584c5cc632ca65640db91b6bacce3a4df6b42ce7cc838833d287"
    143         "db71e509e3fd9b060ddb20ba5c51dcc5948d46fbf640dfe0441782cab85fa4ac",
    144         // https://tools.ietf.org/html/rfc5915
    145         "30770201010420"  // DER-encodeded EC private key header
    146         "7d7dc5f71eb29ddaf80d6214632eeae03d9058af1fb6d22ed80badb62bc1a534"  // private key
    147         "a00a06082a8648ce3d030107a144034200"  // DER-encoded curve OID,
    148         "04"
    149         "ead218590119e8876b29146ff89ca61770c4edbbf97d38ce385ed281d8a6b230"
    150         "28af61281fd35e2fa7002523acc85a429cb06ee6648325389f59edfce1405141",
    151         "46fc62106420ff012e54a434fbdd2d25ccc5852060561e68040dd7778997bd7b",
    152     },
    153     {
    154         KM_EC_CURVE_P_256, "04"
    155                            "809f04289c64348c01515eb03d5ce7ac1a8cb9498f5caa50197e58d43a86a7ae"
    156                            "b29d84e811197f25eba8f5194092cb6ff440e26d4421011372461f579271cda3",
    157         // https://tools.ietf.org/html/rfc5915
    158         "30770201010420"  // DER-encodeded EC private key header
    159         "38f65d6dce47676044d58ce5139582d568f64bb16098d179dbab07741dd5caf5"  // private key
    160         "a00a06082a8648ce3d030107a144034200"  // DER-encoded curve OID,
    161         "04"
    162         "119f2f047902782ab0c9e27a54aff5eb9b964829ca99c06b02ddba95b0a3f6d0"
    163         "8f52b726664cac366fc98ac7a012b2682cbd962e5acb544671d41b9445704d1d",
    164         "057d636096cb80b67a8c038c890e887d1adfa4195e9b3ce241c8a778c59cda67",
    165     },
    166     {
    167         KM_EC_CURVE_P_256, "04"
    168                            "df3989b9fa55495719b3cf46dccd28b5153f7808191dd518eff0c3cff2b705ed"
    169                            "422294ff46003429d739a33206c8752552c8ba54a270defc06e221e0feaf6ac4",
    170         // https://tools.ietf.org/html/rfc5915
    171         "30770201010420"  // DER-encodeded EC private key header
    172         "207c43a79bfee03db6f4b944f53d2fb76cc49ef1c9c4d34d51b6c65c4db6932d"  // private key
    173         "a00a06082a8648ce3d030107a144034200"  // DER-encoded curve OID,
    174         "04"
    175         "24277c33f450462dcb3d4801d57b9ced05188f16c28eda873258048cd1607e0d"
    176         "c4789753e2b1f63b32ff014ec42cd6a69fac81dfe6d0d6fd4af372ae27c46f88",
    177         "96441259534b80f6aee3d287a6bb17b5094dd4277d9e294f8fe73e48bf2a0024",
    178     },
    179 };
    180 
    181 /**
    182  * Test that key exchange works with NIST test vectors.
    183  */
    184 TEST(NistCurveKeyExchange, NistTestVectors) {
    185     for (auto& test : kNistCurveTests) {
    186         string private_key = hex2str(test.my_private_key);
    187         string shared_secret = hex2str(test.shared_secret);
    188 
    189         const uint8_t* private_key_data = reinterpret_cast<const uint8_t*>(private_key.data());
    190         UniquePtr<EC_KEY, EC_KEY_Delete> ec_key(
    191             d2i_ECPrivateKey(nullptr, &private_key_data, private_key.size()));
    192         ASSERT_TRUE(ec_key.get() && EC_KEY_check_key(ec_key.get()));
    193 
    194         keymaster_error_t error;
    195         NistCurveKeyExchange* key_exchange = new NistCurveKeyExchange(ec_key.release(), &error);
    196         EXPECT_EQ(KM_ERROR_OK, error);
    197         ASSERT_TRUE(key_exchange != nullptr);
    198 
    199         Buffer computed_shared_secret;
    200         string peer_public_key = hex2str(test.peer_public_key);
    201         ASSERT_TRUE(key_exchange->CalculateSharedKey(
    202             reinterpret_cast<const uint8_t*>(peer_public_key.data()), peer_public_key.size(),
    203             &computed_shared_secret));
    204         EXPECT_EQ(shared_secret.size(), computed_shared_secret.available_read());
    205         EXPECT_EQ(0, memcmp(shared_secret.data(), computed_shared_secret.peek_read(),
    206                             shared_secret.size()));
    207 
    208         for (size_t i = 0; i < peer_public_key.size(); i++) {
    209             // randomly flip some bits in the peer public key to make it invalid
    210             peer_public_key[i] ^= 0xff;
    211             ASSERT_FALSE(key_exchange->CalculateSharedKey(
    212                 reinterpret_cast<const uint8_t*>(peer_public_key.data()), peer_public_key.size(),
    213                 &computed_shared_secret));
    214         }
    215     }
    216 }
    217 
    218 }  // namespace test
    219 }  // namespace keymaster
    220