/* * 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 #include #include 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; 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 /* EEK pub */, std::vector /* 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 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(*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 /* pubkeys */> validateAndExtractPubkeys(bool testMode, uint32_t numKeys, KeymasterBlob* keysToSign, 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(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& pubkey, const std::vector& 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