gatekeeper.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 <UniquePtr.h>
#include <gatekeeper/gatekeeper.h>

#include <endian.h>

namespace gatekeeper {

void GateKeeper::Enroll(const EnrollRequest &request, EnrollResponse *response) {
    if (response == NULL) return;

    if (!request.provided_password.buffer.get()) {
        response->error = ERROR_INVALID;
        return;
    }

    secure_id_t user_id = 0;

    if (request.password_handle.buffer.get() == NULL) {
        // Password handle does not match what is stored, generate new SecureID
        GetRandom(&user_id, sizeof(secure_id_t));
    } else {
        password_handle_t *pw_handle =
            reinterpret_cast<password_handle_t *>(request.password_handle.buffer.get());
        if (!DoVerify(pw_handle, request.enrolled_password)) {
            // incorrect old password
            response->error = ERROR_INVALID;
            return;
        }

        user_id = pw_handle->user_id;
    }

    salt_t salt;
    GetRandom(&salt, sizeof(salt));

    secure_id_t authenticator_id;
    GetRandom(&authenticator_id, sizeof(authenticator_id));


    SizedBuffer password_handle;
    if(!CreatePasswordHandle(&password_handle,
            salt, user_id, authenticator_id, request.provided_password.buffer.get(),
            request.provided_password.length)) {
        response->error = ERROR_INVALID;
        return;
    }

    response->SetEnrolledPasswordHandle(&password_handle);
}

void GateKeeper::Verify(const VerifyRequest &request, VerifyResponse *response) {
    if (response == NULL) return;

    if (!request.provided_password.buffer.get() || !request.password_handle.buffer.get()) {
        response->error = ERROR_INVALID;
        return;
    }

    password_handle_t *password_handle = reinterpret_cast<password_handle_t *>(
            request.password_handle.buffer.get());

    // Sanity check
    if (password_handle->version != HANDLE_VERSION) {
        response->error = ERROR_INVALID;
        return;
    }

    secure_id_t user_id = password_handle->user_id;
    secure_id_t authenticator_id = password_handle->authenticator_id;

    uint64_t timestamp = GetMillisecondsSinceBoot();

    if (DoVerify(password_handle, request.provided_password)) {
        // Signature matches
        SizedBuffer auth_token;
        MintAuthToken(&auth_token.buffer, &auth_token.length, timestamp,
                user_id, authenticator_id, request.challenge);
        response->SetVerificationToken(&auth_token);
    } else {
        response->error = ERROR_INVALID;
    }
}

bool GateKeeper::CreatePasswordHandle(SizedBuffer *password_handle_buffer, salt_t salt,
        secure_id_t user_id, secure_id_t authenticator_id, const uint8_t *password,
        uint32_t password_length) {
    password_handle_buffer->buffer.reset(new uint8_t[sizeof(password_handle_t)]);
    password_handle_buffer->length = sizeof(password_handle_t);

    password_handle_t *password_handle = reinterpret_cast<password_handle_t *>(
            password_handle_buffer->buffer.get());
    password_handle->version = HANDLE_VERSION;
    password_handle->salt = salt;
    password_handle->user_id = user_id;
    password_handle->authenticator_id = authenticator_id;

    uint32_t metadata_length = sizeof(user_id) /* user id */
        + sizeof(authenticator_id) /* auth id */ + sizeof(HANDLE_VERSION) /* version */;
    uint8_t to_sign[password_length + metadata_length];
    memcpy(to_sign, password_handle, metadata_length);
    memcpy(to_sign + metadata_length, password, password_length);

    const uint8_t *password_key = NULL;
    uint32_t password_key_length = 0;
    GetPasswordKey(&password_key, &password_key_length);

    if (!password_key || password_key_length == 0) {
        return false;
    }

    ComputePasswordSignature(password_handle->signature, sizeof(password_handle->signature),
            password_key, password_key_length, to_sign, sizeof(to_sign), salt);
    return true;
}

bool GateKeeper::DoVerify(const password_handle_t *expected_handle, const SizedBuffer &password) {
    if (!password.buffer.get()) return false;

    SizedBuffer provided_handle;
    if (!CreatePasswordHandle(&provided_handle, expected_handle->salt, expected_handle->user_id,
            expected_handle->authenticator_id, password.buffer.get(), password.length)) {
        return false;
    }

    return memcmp_s(provided_handle.buffer.get(), expected_handle, sizeof(*expected_handle)) == 0;
}

void GateKeeper::MintAuthToken(UniquePtr<uint8_t> *auth_token, uint32_t *length,
        uint64_t timestamp, secure_id_t user_id, secure_id_t authenticator_id,
        uint64_t challenge) {
    if (auth_token == NULL) return;

    hw_auth_token_t *token = new hw_auth_token_t;
    SizedBuffer serialized_auth_token;

    token->version = HW_AUTH_TOKEN_VERSION;
    token->challenge = challenge;
    token->user_id = user_id;
    token->authenticator_id = authenticator_id;
    token->authenticator_type = htonl(HW_AUTH_PASSWORD);
    token->timestamp = htobe64(timestamp);

    const uint8_t *auth_token_key = NULL;
    uint32_t key_len = 0;
    if (GetAuthTokenKey(&auth_token_key, &key_len)) {
        uint32_t hash_len = (uint32_t)((uint8_t *)&token->hmac - (uint8_t *)token);
        ComputeSignature(token->hmac, sizeof(token->hmac), auth_token_key, key_len,
                reinterpret_cast<uint8_t *>(token), hash_len);
    } else {
        memset(token->hmac, 0, sizeof(token->hmac));
    }

    if (length != NULL) *length = sizeof(*token);
    auth_token->reset(reinterpret_cast<uint8_t *>(token));
}

}