contexts/soft_keymaster_context.cpp

/*
 * Copyright 2015 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/contexts/soft_keymaster_context.h>

#include <memory>

#include <openssl/rand.h>

#include <keymaster/android_keymaster_utils.h>
#include <keymaster/key_blob_utils/auth_encrypted_key_blob.h>
#include <keymaster/key_blob_utils/integrity_assured_key_blob.h>
#include <keymaster/key_blob_utils/ocb_utils.h>
#include <keymaster/key_blob_utils/software_keyblobs.h>
#include <keymaster/km_openssl/aes_key.h>
#include <keymaster/km_openssl/asymmetric_key.h>
#include <keymaster/km_openssl/attestation_utils.h>
#include <keymaster/km_openssl/certificate_utils.h>
#include <keymaster/km_openssl/ec_key_factory.h>
#include <keymaster/km_openssl/hmac_key.h>
#include <keymaster/km_openssl/openssl_err.h>
#include <keymaster/km_openssl/rsa_key_factory.h>
#include <keymaster/km_openssl/triple_des_key.h>
#include <keymaster/logger.h>

#include <keymaster/contexts/soft_attestation_cert.h>

using std::unique_ptr;

namespace keymaster {

namespace {

KeymasterBlob string2Blob(const std::string& str) {
    return KeymasterBlob(reinterpret_cast<const uint8_t*>(str.data()), str.size());
}

}  // anonymous namespace

SoftKeymasterContext::SoftKeymasterContext(KmVersion version, const std::string& root_of_trust)
    : SoftAttestationContext(version),  //
      rsa_factory_(new RsaKeyFactory(*this /* blob_maker */, *this /* context */)),
      ec_factory_(new EcKeyFactory(*this /* blob_maker */, *this /* context */)),
      aes_factory_(new AesKeyFactory(*this /* blob_maker */, *this /* random_source */)),
      tdes_factory_(new TripleDesKeyFactory(*this /* blob_maker */, *this /* random_source */)),
      hmac_factory_(new HmacKeyFactory(*this /* blob_maker */, *this /* random_source */)),
      root_of_trust_(string2Blob(root_of_trust)), os_version_(0), os_patchlevel_(0) {}

SoftKeymasterContext::~SoftKeymasterContext() {}

keymaster_error_t SoftKeymasterContext::SetSystemVersion(uint32_t os_version,
                                                         uint32_t os_patchlevel) {
    os_version_ = os_version;
    os_patchlevel_ = os_patchlevel;
    return KM_ERROR_OK;
}

void SoftKeymasterContext::GetSystemVersion(uint32_t* os_version, uint32_t* os_patchlevel) const {
    *os_version = os_version_;
    *os_patchlevel = os_patchlevel_;
}

KeyFactory* SoftKeymasterContext::GetKeyFactory(keymaster_algorithm_t algorithm) const {
    switch (algorithm) {
    case KM_ALGORITHM_RSA:
        return rsa_factory_.get();
    case KM_ALGORITHM_EC:
        return ec_factory_.get();
    case KM_ALGORITHM_AES:
        return aes_factory_.get();
    case KM_ALGORITHM_TRIPLE_DES:
        return tdes_factory_.get();
    case KM_ALGORITHM_HMAC:
        return hmac_factory_.get();
    default:
        return nullptr;
    }
}

OperationFactory* SoftKeymasterContext::GetOperationFactory(keymaster_algorithm_t algorithm,
                                                            keymaster_purpose_t purpose) const {
    KeyFactory* key_factory = GetKeyFactory(algorithm);
    if (!key_factory) return nullptr;
    return key_factory->GetOperationFactory(purpose);
}

static keymaster_error_t TranslateAuthorizationSetError(AuthorizationSet::Error err) {
    switch (err) {
    case AuthorizationSet::OK:
        return KM_ERROR_OK;
    case AuthorizationSet::ALLOCATION_FAILURE:
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    case AuthorizationSet::MALFORMED_DATA:
        return KM_ERROR_UNKNOWN_ERROR;
    }
    return KM_ERROR_OK;
}

static keymaster_error_t SetAuthorizations(const AuthorizationSet& key_description,
                                           keymaster_key_origin_t origin, uint32_t os_version,
                                           uint32_t os_patchlevel, AuthorizationSet* hw_enforced,
                                           AuthorizationSet* sw_enforced) {
    sw_enforced->Clear();

    for (auto& entry : key_description) {
        switch (entry.tag) {
        // These cannot be specified by the client.
        case KM_TAG_ROOT_OF_TRUST:
        case KM_TAG_ORIGIN:
            LOG_E("Root of trust and origin tags may not be specified", 0);
            return KM_ERROR_INVALID_TAG;

        // These don't work.
        case KM_TAG_ROLLBACK_RESISTANT:
            LOG_E("KM_TAG_ROLLBACK_RESISTANT not supported", 0);
            return KM_ERROR_UNSUPPORTED_TAG;

        // These are hidden.
        case KM_TAG_APPLICATION_ID:
        case KM_TAG_APPLICATION_DATA:
            break;

        // Everything else we just copy into sw_enforced, unless the KeyFactory has placed it in
        // hw_enforced, in which case we defer to its decision.
        default:
            if (hw_enforced->GetTagCount(entry.tag) == 0) sw_enforced->push_back(entry);
            break;
        }
    }

    sw_enforced->push_back(TAG_CREATION_DATETIME, java_time(time(nullptr)));
    sw_enforced->push_back(TAG_ORIGIN, origin);
    sw_enforced->push_back(TAG_OS_VERSION, os_version);
    sw_enforced->push_back(TAG_OS_PATCHLEVEL, os_patchlevel);

    return TranslateAuthorizationSetError(sw_enforced->is_valid());
}

keymaster_error_t SoftKeymasterContext::CreateKeyBlob(const AuthorizationSet& key_description,
                                                      const keymaster_key_origin_t origin,
                                                      const KeymasterKeyBlob& key_material,
                                                      KeymasterKeyBlob* blob,
                                                      AuthorizationSet* hw_enforced,
                                                      AuthorizationSet* sw_enforced) const {
    keymaster_error_t error = SetAuthorizations(key_description, origin, os_version_,
                                                os_patchlevel_, hw_enforced, sw_enforced);
    if (error != KM_ERROR_OK) return error;

    AuthorizationSet hidden;
    error = BuildHiddenAuthorizations(key_description, &hidden, root_of_trust_);
    if (error != KM_ERROR_OK) return error;

    return SerializeIntegrityAssuredBlob(key_material, hidden, *hw_enforced, *sw_enforced, blob);
}

keymaster_error_t SoftKeymasterContext::UpgradeKeyBlob(const KeymasterKeyBlob& key_to_upgrade,
                                                       const AuthorizationSet& upgrade_params,
                                                       KeymasterKeyBlob* upgraded_key) const {
    UniquePtr<Key> key;
    keymaster_error_t error = ParseKeyBlob(key_to_upgrade, upgrade_params, &key);
    if (error != KM_ERROR_OK) return error;

    return UpgradeSoftKeyBlob(key, os_version_, os_patchlevel_, upgrade_params, upgraded_key);
}

keymaster_error_t SoftKeymasterContext::ParseKeyBlob(const KeymasterKeyBlob& blob,
                                                     const AuthorizationSet& additional_params,
                                                     UniquePtr<Key>* key) const {
    // This is a little bit complicated.
    //
    // The SoftKeymasterContext has to handle a lot of different kinds of key blobs.
    //
    // 1.  New keymaster1 software key blobs.  These are integrity-assured but not encrypted.  The
    //     raw key material and auth sets should be extracted and returned.  This is the kind
    //     produced by this context when the KeyFactory doesn't use keymaster0 to back the keys.
    //
    // 2.  Old keymaster1 software key blobs.  These are OCB-encrypted with an all-zero master key.
    //     They should be decrypted and the key material and auth sets extracted and returned.
    //
    // 3.  Old keymaster0 software key blobs.  These are raw key material with a small header tacked
    //     on the front.  They don't have auth sets, so reasonable defaults are generated and
    //     returned along with the raw key material.
    //
    // 4.  New keymaster0 hardware key blobs.  These are integrity-assured but not encrypted (though
    //     they're protected by the keymaster0 hardware implementation).  The keymaster0 key blob
    //     and auth sets should be extracted and returned.
    //
    // 5.  Keymaster1 hardware key blobs.  These are raw hardware key blobs.  They contain auth
    //     sets, which we retrieve from the hardware module.
    //
    // 6.  Old keymaster0 hardware key blobs.  These are raw hardware key blobs.  They don't have
    //     auth sets so reasonable defaults are generated and returned along with the key blob.
    //
    // Determining what kind of blob has arrived is somewhat tricky.  What helps is that
    // integrity-assured and OCB-encrypted blobs are self-consistent and effectively impossible to
    // parse as anything else.  Old keymaster0 software key blobs have a header.  It's reasonably
    // unlikely that hardware keys would have the same header.  So anything that is neither
    // integrity-assured nor OCB-encrypted and lacks the old software key header is assumed to be
    // keymaster0 hardware.

    AuthorizationSet hw_enforced;
    AuthorizationSet sw_enforced;
    KeymasterKeyBlob key_material;
    AuthorizationSet hidden;
    keymaster_error_t error;

    auto constructKey = [&, this]() mutable -> keymaster_error_t {
        // GetKeyFactory
        if (error != KM_ERROR_OK) return error;
        keymaster_algorithm_t algorithm;
        if (!hw_enforced.GetTagValue(TAG_ALGORITHM, &algorithm) &&
            !sw_enforced.GetTagValue(TAG_ALGORITHM, &algorithm)) {
            return KM_ERROR_INVALID_ARGUMENT;
        }
        auto factory = GetKeyFactory(algorithm);
        return factory->LoadKey(move(key_material), additional_params, move(hw_enforced),
                                move(sw_enforced), key);
    };

    error = BuildHiddenAuthorizations(additional_params, &hidden, root_of_trust_);
    if (error != KM_ERROR_OK) return error;

    // Assume it's an integrity-assured blob (new software-only blob, or new keymaster0-backed
    // blob).
    error =
        DeserializeIntegrityAssuredBlob(blob, hidden, &key_material, &hw_enforced, &sw_enforced);
    if (error != KM_ERROR_INVALID_KEY_BLOB) return constructKey();

    // Wasn't an integrity-assured blob.  Maybe it's an Auth-encrypted blob.
    error = ParseAuthEncryptedBlob(blob, hidden, &key_material, &hw_enforced, &sw_enforced);
    if (error == KM_ERROR_OK) LOG_D("Parsed an old keymaster1 software key", 0);
    if (error != KM_ERROR_INVALID_KEY_BLOB) return constructKey();

    // Wasn't an OCB-encrypted blob.  Maybe it's an old softkeymaster blob.
    error = ParseOldSoftkeymasterBlob(blob, &key_material, &hw_enforced, &sw_enforced);
    if (error == KM_ERROR_OK) LOG_D("Parsed an old sofkeymaster key", 0);
    if (error != KM_ERROR_INVALID_KEY_BLOB) return constructKey();

    return KM_ERROR_INVALID_KEY_BLOB;
}

keymaster_error_t SoftKeymasterContext::DeleteKey(const KeymasterKeyBlob& /* blob */) const {
    // Nothing to do for software-only contexts.
    return KM_ERROR_OK;
}

keymaster_error_t SoftKeymasterContext::DeleteAllKeys() const {
    return KM_ERROR_OK;
}

keymaster_error_t SoftKeymasterContext::AddRngEntropy(const uint8_t* buf, size_t length) const {
    RAND_add(buf, length, 0 /* Don't assume any entropy is added to the pool. */);
    return KM_ERROR_OK;
}

CertificateChain
SoftKeymasterContext::GenerateAttestation(const Key& key,  //
                                          const AuthorizationSet& attest_params,
                                          UniquePtr<Key> /* attest_key */,
                                          const KeymasterBlob& /* issuer_subject */,  //
                                          keymaster_error_t* error) const {
    keymaster_algorithm_t key_algorithm;
    if (!key.authorizations().GetTagValue(TAG_ALGORITHM, &key_algorithm)) {
        *error = KM_ERROR_UNKNOWN_ERROR;
        return {};
    }

    if ((key_algorithm != KM_ALGORITHM_RSA && key_algorithm != KM_ALGORITHM_EC)) {
        *error = KM_ERROR_INCOMPATIBLE_ALGORITHM;
        return {};
    }

    // We have established that the given key has the correct algorithm, and because this is the
    // SoftKeymasterContext we can assume that the Key is an AsymmetricKey. So we can downcast.
    const AsymmetricKey& asymmetric_key = static_cast<const AsymmetricKey&>(key);

    return generate_attestation(asymmetric_key, attest_params, {} /* attest_key */, *this, error);
}

CertificateChain SoftKeymasterContext::GenerateSelfSignedCertificate(
    const Key& key, const AuthorizationSet& cert_params, bool fake_signature,
    keymaster_error_t* error) const {
    keymaster_algorithm_t key_algorithm;
    if (!key.authorizations().GetTagValue(TAG_ALGORITHM, &key_algorithm)) {
        *error = KM_ERROR_UNKNOWN_ERROR;
        return {};
    }

    if ((key_algorithm != KM_ALGORITHM_RSA && key_algorithm != KM_ALGORITHM_EC)) {
        *error = KM_ERROR_INCOMPATIBLE_ALGORITHM;
        return {};
    }

    // We have established that the given key has the correct algorithm, and because this is the
    // SoftKeymasterContext we can assume that the Key is an AsymmetricKey. So we can downcast.
    const AsymmetricKey& asymmetric_key = static_cast<const AsymmetricKey&>(key);

    return generate_self_signed_cert(asymmetric_key, cert_params, fake_signature, error);
}

keymaster_error_t SoftKeymasterContext::UnwrapKey(const KeymasterKeyBlob&, const KeymasterKeyBlob&,
                                                  const AuthorizationSet&, const KeymasterKeyBlob&,
                                                  AuthorizationSet*, keymaster_key_format_t*,
                                                  KeymasterKeyBlob*) const {
    return KM_ERROR_UNIMPLEMENTED;
}

}  // namespace keymaster