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/soft_keymaster_context.h>

#include <memory>
#include <time.h>

#include <openssl/aes.h>
#include <openssl/rand.h>
#include <openssl/sha.h>

#include <keymaster/android_keymaster_utils.h>
#include <keymaster/logger.h>

#include "aes_key.h"
#include "auth_encrypted_key_blob.h"
#include "ec_keymaster0_key.h"
#include "hmac_key.h"
#include "integrity_assured_key_blob.h"
#include "keymaster0_engine.h"
#include "ocb_utils.h"
#include "openssl_err.h"
#include "rsa_keymaster0_key.h"

using std::unique_ptr;

namespace keymaster {

namespace {
static uint8_t master_key_bytes[AES_BLOCK_SIZE] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
const int NONCE_LENGTH = 12;
const int TAG_LENGTH = 16;
const KeymasterKeyBlob MASTER_KEY(master_key_bytes, array_length(master_key_bytes));
}  // anonymous namespace

SoftKeymasterContext::SoftKeymasterContext(keymaster0_device_t* keymaster0_device) {
    if (keymaster0_device && (keymaster0_device->flags & KEYMASTER_SOFTWARE_ONLY) == 0)
        engine_.reset(new Keymaster0Engine(keymaster0_device));
    rsa_factory_.reset(new RsaKeymaster0KeyFactory(this, engine_.get()));
    ec_factory_.reset(new EcdsaKeymaster0KeyFactory(this, engine_.get()));
    aes_factory_.reset(new AesKeyFactory(this));
    hmac_factory_.reset(new HmacKeyFactory(this));
}

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_HMAC:
        return hmac_factory_.get();
    default:
        return nullptr;
    }
}

static keymaster_algorithm_t supported_algorithms[] = {KM_ALGORITHM_RSA, KM_ALGORITHM_EC,
                                                       KM_ALGORITHM_AES, KM_ALGORITHM_HMAC};

keymaster_algorithm_t*
SoftKeymasterContext::GetSupportedAlgorithms(size_t* algorithms_count) const {
    *algorithms_count = array_length(supported_algorithms);
    return supported_algorithms;
}

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 BuildHiddenAuthorizations(const AuthorizationSet& input_set,
                                                   AuthorizationSet* hidden) {
    keymaster_blob_t entry;
    if (input_set.GetTagValue(TAG_APPLICATION_ID, &entry))
        hidden->push_back(TAG_APPLICATION_ID, entry.data, entry.data_length);
    if (input_set.GetTagValue(TAG_APPLICATION_DATA, &entry))
        hidden->push_back(TAG_APPLICATION_DATA, entry.data, entry.data_length);

    keymaster_key_param_t root_of_trust;
    root_of_trust.tag = KM_TAG_ROOT_OF_TRUST;
    root_of_trust.blob.data = reinterpret_cast<const uint8_t*>("SW");
    root_of_trust.blob.data_length = 2;
    hidden->push_back(root_of_trust);

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

static keymaster_error_t SetAuthorizations(const AuthorizationSet& key_description,
                                           keymaster_key_origin_t origin,
                                           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(NULL)));
    sw_enforced->push_back(TAG_ORIGIN, origin);
    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, hw_enforced, sw_enforced);
    if (error != KM_ERROR_OK)
        return error;

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

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

static keymaster_error_t ParseOcbAuthEncryptedBlob(const KeymasterKeyBlob& blob,
                                                   const AuthorizationSet& hidden,
                                                   KeymasterKeyBlob* key_material,
                                                   AuthorizationSet* hw_enforced,
                                                   AuthorizationSet* sw_enforced) {
    Buffer nonce, tag;
    KeymasterKeyBlob encrypted_key_material;
    keymaster_error_t error = DeserializeAuthEncryptedBlob(blob, &encrypted_key_material,
                                                           hw_enforced, sw_enforced, &nonce, &tag);
    if (error != KM_ERROR_OK)
        return error;

    if (nonce.available_read() != OCB_NONCE_LENGTH || tag.available_read() != OCB_TAG_LENGTH)
        return KM_ERROR_INVALID_KEY_BLOB;

    return OcbDecryptKey(*hw_enforced, *sw_enforced, hidden, MASTER_KEY, encrypted_key_material,
                         nonce, tag, key_material);
}

// Note: This parsing code in below is from system/security/softkeymaster/keymaster_openssl.cpp's
// unwrap_key function, modified for the preferred function signature and formatting.  It does some
// odd things, but they have been left unchanged to avoid breaking compatibility.
static const uint8_t SOFT_KEY_MAGIC[] = {'P', 'K', '#', '8'};
const uint64_t HUNDRED_YEARS = 1000LL * 60 * 60 * 24 * 365 * 100;
static keymaster_error_t ParseOldSoftkeymasterBlob(const KeymasterKeyBlob& blob,
                                                   KeymasterKeyBlob* key_material,
                                                   AuthorizationSet* hw_enforced,
                                                   AuthorizationSet* sw_enforced) {
    long publicLen = 0;
    long privateLen = 0;
    const uint8_t* p = blob.key_material;
    const uint8_t* end = blob.key_material + blob.key_material_size;

    int type = 0;
    ptrdiff_t min_size =
        sizeof(SOFT_KEY_MAGIC) + sizeof(type) + sizeof(publicLen) + 1 + sizeof(privateLen) + 1;
    if (end - p < min_size) {
        LOG_W("key blob appears to be truncated (if an old SW key)", 0);
        return KM_ERROR_INVALID_KEY_BLOB;
    }

    if (memcmp(p, SOFT_KEY_MAGIC, sizeof(SOFT_KEY_MAGIC)) != 0)
        return KM_ERROR_INVALID_KEY_BLOB;
    p += sizeof(SOFT_KEY_MAGIC);

    for (size_t i = 0; i < sizeof(type); i++)
        type = (type << 8) | *p++;

    for (size_t i = 0; i < sizeof(type); i++)
        publicLen = (publicLen << 8) | *p++;

    if (p + publicLen > end) {
        LOG_W("public key length encoding error: size=%ld, end=%td", publicLen, end - p);
        return KM_ERROR_INVALID_KEY_BLOB;
    }
    p += publicLen;

    if (end - p < 2) {
        LOG_W("key blob appears to be truncated (if an old SW key)", 0);
        return KM_ERROR_INVALID_KEY_BLOB;
    }

    for (size_t i = 0; i < sizeof(type); i++)
        privateLen = (privateLen << 8) | *p++;

    if (p + privateLen > end) {
        LOG_W("private key length encoding error: size=%ld, end=%td", privateLen, end - p);
        return KM_ERROR_INVALID_KEY_BLOB;
    }

    // Just to be sure, make sure that the ASN.1 structure parses correctly.  We don't actually use
    // the EVP_PKEY here.
    unique_ptr<EVP_PKEY, EVP_PKEY_Delete> pkey(EVP_PKEY_new());
    if (pkey.get() == nullptr)
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;

    EVP_PKEY* tmp = pkey.get();
    const uint8_t* key_start = p;
    if (d2i_PrivateKey(type, &tmp, &p, privateLen) == NULL) {
        LOG_W("Failed to parse PKCS#8 key material (if old SW key)", 0);
        return KM_ERROR_INVALID_KEY_BLOB;
    }

    if (!key_material->Reset(privateLen))
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    memcpy(key_material->writable_data(), key_start, privateLen);

    hw_enforced->Clear();
    sw_enforced->Clear();

    switch (type) {
    case EVP_PKEY_RSA:
        sw_enforced->push_back(TAG_ALGORITHM, KM_ALGORITHM_RSA);
        sw_enforced->push_back(TAG_DIGEST, KM_DIGEST_NONE);
        sw_enforced->push_back(TAG_PADDING, KM_PAD_NONE);
        break;

    case EVP_PKEY_EC:
        sw_enforced->push_back(TAG_ALGORITHM, KM_ALGORITHM_RSA);
        sw_enforced->push_back(TAG_DIGEST, KM_DIGEST_NONE);
        break;

    case EVP_PKEY_DSA:
        return KM_ERROR_UNSUPPORTED_ALGORITHM;

    default:
        return KM_ERROR_INVALID_KEY_BLOB;
    }

    sw_enforced->push_back(TAG_PURPOSE, KM_PURPOSE_SIGN);
    sw_enforced->push_back(TAG_PURPOSE, KM_PURPOSE_VERIFY);
    sw_enforced->push_back(TAG_ALL_USERS);
    sw_enforced->push_back(TAG_NO_AUTH_REQUIRED);
    uint64_t now = java_time(time(NULL));
    sw_enforced->push_back(TAG_CREATION_DATETIME, now);
    sw_enforced->push_back(TAG_ORIGINATION_EXPIRE_DATETIME, now + HUNDRED_YEARS);
    sw_enforced->push_back(TAG_DIGEST, KM_DIGEST_NONE);
    sw_enforced->push_back(TAG_PADDING, KM_PAD_NONE);

    return KM_ERROR_OK;
}

keymaster_error_t SoftKeymasterContext::ParseKeyBlob(const KeymasterKeyBlob& blob,
                                                     const AuthorizationSet& additional_params,
                                                     KeymasterKeyBlob* key_material,
                                                     AuthorizationSet* hw_enforced,
                                                     AuthorizationSet* sw_enforced) 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.  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 hidden;
    keymaster_error_t error = BuildHiddenAuthorizations(additional_params, &hidden);
    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 error;

    // Wasn't an integrity-assured blob.  Maybe it's an OCB-encrypted blob.
    error = ParseOcbAuthEncryptedBlob(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 error;

    // 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 error;

    // Not an old softkeymaster blob, either.  The only remaining option is old HW keymaster0.
    if (!engine_)
        return KM_ERROR_INVALID_KEY_BLOB;

    // See if the HW thinks it's valid.
    unique_ptr<EVP_PKEY, EVP_PKEY_Delete> tmp_key(engine_->GetKeymaster0PublicKey(blob));
    if (!tmp_key)
        return KM_ERROR_INVALID_KEY_BLOB;

    *key_material = blob;
    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;
}

keymaster_error_t SoftKeymasterContext::GenerateRandom(uint8_t* buf, size_t length) const {
    if (RAND_bytes(buf, length) != 1)
        return KM_ERROR_UNKNOWN_ERROR;
    return KM_ERROR_OK;
}

}  // namespace keymaster