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/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "keymaster/cppcose/cppcose.h"
#include <keymaster/logger.h>
#include <keymaster/remote_provisioning_utils.h>
#include <string_view>
namespace keymaster {
using cppcose::ALGORITHM;
using cppcose::COSE_KEY;
using cppcose::CoseKey;
using cppcose::CoseKeyCurve;
using cppcose::EC2;
using cppcose::ECDH_ES_HKDF_256;
using cppcose::ES256;
using cppcose::generateCoseMac0Mac;
using cppcose::HMAC_256;
using cppcose::kCoseMac0EntryCount;
using cppcose::kCoseMac0Payload;
using cppcose::kCoseMac0ProtectedParams;
using cppcose::kCoseMac0Tag;
using cppcose::kCoseMac0UnprotectedParams;
using cppcose::KEY_ID;
using cppcose::OCTET_KEY_PAIR;
using cppcose::P256;
using cppcose::verifyAndParseCoseSign1;
using byte_view = std::basic_string_view<uint8_t>;
struct KeyInfo {
CoseKeyCurve curve;
byte_view pubkey;
// Note: There's no need to include algorithm here, since it is assumed
// that all root keys are EDDSA.
bool operator==(const KeyInfo& other) const {
return curve == other.curve && pubkey == other.pubkey;
}
};
// The production root signing key for Google Endpoint Encryption Key cert chains.
inline constexpr uint8_t kGeekRoot[] = {
0x99, 0xB9, 0xEE, 0xDD, 0x5E, 0xE4, 0x52, 0xF6, 0x85, 0xC6, 0x4C, 0x62, 0xDC, 0x3E, 0x61, 0xAB,
0x57, 0x48, 0x7D, 0x75, 0x37, 0x29, 0xAD, 0x76, 0x80, 0x32, 0xD2, 0xB3, 0xCB, 0x63, 0x58, 0xD9};
// Hard-coded set of acceptable public COSE_Keys that can act as roots of EEK chains.
inline constexpr KeyInfo kAuthorizedEekRoots[] = {
{CoseKeyCurve::ED25519, byte_view(kGeekRoot, sizeof(kGeekRoot))},
};
StatusOr<std::pair<std::vector<uint8_t> /* EEK pub */, std::vector<uint8_t> /* EEK ID */>>
validateAndExtractEekPubAndId(bool testMode, const KeymasterBlob& endpointEncryptionCertChain) {
auto [item, newPos, errMsg] =
cppbor::parse(endpointEncryptionCertChain.begin(), endpointEncryptionCertChain.end());
if (!item || !item->asArray()) {
LOG_E("Error parsing EEK chain: %s", errMsg.c_str());
return kStatusFailed;
}
const cppbor::Array* certArr = item->asArray();
std::vector<uint8_t> lastPubKey;
for (size_t i = 0; i < certArr->size(); ++i) {
auto cosePubKey =
verifyAndParseCoseSign1(certArr->get(i)->asArray(), lastPubKey, {} /* AAD */);
if (!cosePubKey) {
LOG_E("Failed to validate EEK chain: %s", cosePubKey.moveMessage().c_str());
return kStatusInvalidEek;
}
lastPubKey = *std::move(cosePubKey);
// In prod mode the first pubkey should match a well-known Google public key.
if (!testMode && i == 0) {
auto parsedPubKey = CoseKey::parse(lastPubKey);
if (!parsedPubKey) {
LOG_E("%s", parsedPubKey.moveMessage().c_str());
return kStatusFailed;
}
auto curve = parsedPubKey->getIntValue(CoseKey::CURVE);
if (!curve) {
LOG_E("Key is missing required label 'CURVE'", 0);
return kStatusInvalidEek;
}
auto rawPubKey = parsedPubKey->getBstrValue(CoseKey::PUBKEY_X);
if (!rawPubKey) {
LOG_E("Key is missing required label 'PUBKEY_X'", 0);
return kStatusInvalidEek;
}
KeyInfo matcher = {static_cast<CoseKeyCurve>(*curve),
byte_view(rawPubKey->data(), rawPubKey->size())};
if (std::find(std::begin(kAuthorizedEekRoots), std::end(kAuthorizedEekRoots),
matcher) == std::end(kAuthorizedEekRoots)) {
LOG_E("Unrecognized root of EEK chain", 0);
return kStatusInvalidEek;
}
}
}
auto eek = CoseKey::parseX25519(lastPubKey, true /* requireKid */);
if (!eek) {
LOG_E("Failed to get EEK: %s", eek.moveMessage().c_str());
return kStatusInvalidEek;
}
return std::make_pair(eek->getBstrValue(CoseKey::PUBKEY_X).value(),
eek->getBstrValue(CoseKey::KEY_ID).value());
}
StatusOr<std::vector<uint8_t> /* pubkeys */>
validateAndExtractPubkeys(bool testMode, uint32_t numKeys, KeymasterBlob* keysToSign,
const cppcose::HmacSha256Function& macFunction) {
auto pubKeysToMac = cppbor::Array();
for (size_t i = 0; i < numKeys; i++) {
auto [macedKeyItem, _, coseMacErrMsg] =
cppbor::parse(keysToSign[i].begin(), keysToSign[i].end());
if (!macedKeyItem || !macedKeyItem->asArray() ||
macedKeyItem->asArray()->size() != kCoseMac0EntryCount) {
LOG_E("Invalid COSE_Mac0 structure", 0);
return kStatusFailed;
}
auto protectedParms = macedKeyItem->asArray()->get(kCoseMac0ProtectedParams)->asBstr();
auto unprotectedParms = macedKeyItem->asArray()->get(kCoseMac0UnprotectedParams)->asMap();
auto payload = macedKeyItem->asArray()->get(kCoseMac0Payload)->asBstr();
auto tag = macedKeyItem->asArray()->get(kCoseMac0Tag)->asBstr();
if (!protectedParms || !unprotectedParms || !payload || !tag) {
LOG_E("Invalid COSE_Mac0 contents", 0);
return kStatusFailed;
}
auto [protectedMap, __, errMsg] = cppbor::parse(protectedParms);
if (!protectedMap || !protectedMap->asMap()) {
LOG_E("Invalid Mac0 protected: %s", errMsg.c_str());
return kStatusFailed;
}
auto& algo = protectedMap->asMap()->get(ALGORITHM);
if (!algo || !algo->asInt() || algo->asInt()->value() != HMAC_256) {
LOG_E("Unsupported Mac0 algorithm", 0);
return kStatusFailed;
}
auto pubKey = CoseKey::parse(payload->value(), EC2, ES256, P256);
if (!pubKey) {
LOG_E("%s", pubKey.moveMessage().c_str());
return kStatusFailed;
}
bool testKey = static_cast<bool>(pubKey->getMap().get(CoseKey::TEST_KEY));
if (testMode && !testKey) {
LOG_E("Production key in test request", 0);
return kStatusProductionKeyInTestRequest;
} else if (!testMode && testKey) {
LOG_E("Test key in production request", 0);
return kStatusTestKeyInProductionRequest;
}
auto macTag = generateCoseMac0Mac(macFunction, {} /* external_aad */, payload->value());
if (!macTag) {
LOG_E("%s", macTag.moveMessage().c_str());
return kStatusInvalidMac;
}
if (macTag->size() != tag->value().size() ||
CRYPTO_memcmp(macTag->data(), tag->value().data(), macTag->size()) != 0) {
LOG_E("MAC tag mismatch", 0);
return kStatusInvalidMac;
}
pubKeysToMac.add(pubKey->moveMap());
}
return pubKeysToMac.encode();
}
cppbor::Array buildCertReqRecipients(const std::vector<uint8_t>& pubkey,
const std::vector<uint8_t>& kid) {
return cppbor::Array() // Array of recipients
.add(cppbor::Array() // Recipient
.add(cppbor::Map() // Protected
.add(ALGORITHM, ECDH_ES_HKDF_256)
.canonicalize()
.encode())
.add(cppbor::Map() // Unprotected
.add(COSE_KEY, cppbor::Map()
.add(CoseKey::KEY_TYPE, OCTET_KEY_PAIR)
.add(CoseKey::CURVE, cppcose::X25519)
.add(CoseKey::PUBKEY_X, pubkey)
.canonicalize())
.add(KEY_ID, kid)
.canonicalize())
.add(cppbor::Null())); // No ciphertext
}
} // namespace keymaster
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