Bitfrost/lang-ja
- This is an on-going translation
Bitfrost(ビットフロスト)とはOLPCのセキュリティ・プラットフォームです。このページでこれから続く内容は、非テクニカル的に紹介した、私たちが解決しようとするセキュリティ問題やそれに関した私たちの目標とそれに基づいた原理です。内容は完全Bitfrost specification(ビットフロスト・スペック)かlocal wiki version(ローカルwikiバージョン)から来ています。それらに付いて、公開のOLPC security mailing list(セキュリティ・メーリングリスト)を通してぜひ 議論に参加できるよう願っています。
紹介と要約
1971年にAT&Tの二人のプログラマー、Ken Thompson (ケン・トンプソン)とDennis Ritchie (デニス・リッチー)が初バージョンのUNIX(ユニックス)をリリースしました。そのオペレーティングシステムは1969年にUNICS(ユニックス)として収入なしのボランティアプロジェクトから始まりました。プログラマー達がテキストプロセッシング・サポートを加える申し出をした時に名前の変更とBell Labs (ベル・ラブス)からの正式な財政援助を得ました。UNIXの大まかなデザインの思いつきは現代まで残っています。人気のあるLinux (リナックス)、FreeBSD (フリーBSD)などのサーバ・オペレーティングシステムや、その他の様々なシステムは基本的に同じUNIX (ユニックス)のデザインを共用しています。
1971年バージョンのUNIX (ユニックス)はuser files (ユーザファイル)で以下のsecurity permissions (セキュリティパーミッション)をサポートしていました。
- non-owner (ノンオウナー／非保有者)はファイルを'change'(チェンジ／変更)できる (write) (ライト／書き込み)
- non-owner (ノンオウナー／非保有者)はファイルが'read'(リード／読む)できる
- owner (オウナー／保有者)はファイルを'change'(チェンジ／変更)できる (write) (ライト／書き込み)
- owner (オウナー／保有者)はファイルが'read'(リード／読む)できる
- ファイルは'execute' (エクセキュート／実行)できる
- ファイルは'set-uid' (setuid／セット・ユー・アイ・ディー)にする
これらのパーミッションはよく見たことがあるでしょう。その理由は、現在ユーザが使うオペレーティングシステムの上での、ファイルにセットできるセキュリティ・パーミッションにそっくりだからです。このパーミッションであまり信じられなくて大変心配なのは、それが昔から現在まで変わりなく、個人ドキュメントの上でユーザが手元に持っているほぼ唯一のコントロールメカニズムだからです。ユーザは同じシステムを共用する他のユーザからファイルを守る事はできますが、自分のプログラムがファイルでいったい何ができるとかのコントロールはまったくありません。
それは1971年には承知されたでしょう: ウェブが現れる20年前でしたし、ほとんどのコンピュータユーザに当てはまる脅威モデルも今とは全く違っていました。だが、しかし、我々の守りが35年間の間に何も変わっていない状態なので、未だにウィールスやマルウェアを止められないのは当然ではないでしょうか？
The crux of the problem lies in the assumption that any program executing on
a system on the user's behalf should have the exact same abilities and
permissions as any other program executing on behalf of the same user. 1971 was
seven years before the first ever international packet-switched network came
into existence. And the first wide-area network using TCP/IP, the communication
suite used by the modern Internet, wasn't created until 1983, twelve years
after Thompson and Ritchie designed the file permissions we're discussing. The
bottom line is that in 1971, there was almost no conceivable way a program
could "come to exist" on a computer except if the account owner — the user —
physically transported it to a machine (for instance, on punched tape), or
entered it there manually. And so the "all or nothing" security approach, where
executing programs have full control over their owner's account, made quite a
lot of sense: any code the user executed, she ipso facto trusted for all
practical purposes.
Fast forward to today, and the situation couldn't be more different: the starkest contrast is perhaps the Web, where a user's web browser executes untrusted scripting code on just about every web page she visits! Browsers are growing increasingly complex sandboxing systems that try to restrict the abilities of such web scripts, but even the latest browser versions are still fixing bugs in their scripting engine implementations. And don't forget e-mail: anyone can send a user an executable program, and for many years the users' instinctive reaction was to open the attachment and run the program. Untrusted code is everywhere, and the only defense seems to be tedious user training and anti-virus software — the latter assuming it's fully updated, and assuming the anti-virus makers have had time to deconstruct each latest virus and construct a defense for it.
Most technologies and approaches that constitute the Bitfrost platform do not represent original research: they have been known in the security literature for years, some of them have been deployed in the field, and others are being tested in the lab. What makes the OLPC XO laptops notable, however, is that they represent the first time that all these security measures have been carefully put together on a system slated to be introduced to tens or hundreds of millions of users. The laptops are also possibly the first time that a mainstream computing product has been willing to give up compatibility with legacy programs in order to achieve strong security. As an example, you'll find that talk about anti-virus and anti-spyware technology is conspicuously absent from the Bitfrost specification, because the security platform on the XO laptops largely renders these issues moot.
We have set out to create a system that is both drastically more secure and provides drastically more usable security than any mainstream system currently on the market. One result of the dedication to usability is that there is only one protection provided by the Bitfrost platform that requires user response, and even then, it's a simple 'yes or no' question understandable even by young children. The remainder of the security is provided behind the scenes. But pushing the envelope on both security and usability is a tall order, and it's important to note that we have neither tried to create, nor do we believe we have created, a "perfectly secure" system. Notions of perfect security in the real world are foolish, and we distance ourselves up front from any such claims.
The Bitfrost approach
Principles
- Open design
- The laptop's security must not depend upon a secret design implemented in hardware or software.
- No lockdown
- Though in their default settings, the laptop's security systems may impose various prohibitions on the user's actions, there must exist a way for these security systems to be disabled. When that is the case, the machine will grant the user complete control.
- No reading required
- Security cannot depend upon the user's ability to read a message from the computer and act in an informed and sensible manner. While disabling a particular security mechanism may require reading, a machine must be secure out of the factory if given to a user who cannot yet read.
- Unobtrusive security
- Whenever possible, the security on the machines must be behind the scenes, making its presence known only through subtle visual or audio cues, and never getting in the user's way. Whenever in conflict with slight user convenience, strong unobtrusive security is to take precedence, though utmost care must be taken to ensure such allowances do not seriously or conspicuously reduce the usability of the machines. As an example, if a program is found attempting to violate a security setting, the user will not be prompted to permit the action; the action will simply be denied. If the user wishes to grant permission for such an action, she can do so through the graphical security center interface.
Goals
- No user passwords
- With users as young as 5 years old, the security of the laptop cannot depend on the user's ability to remember a password. Users cannot be expected to choose passwords when they first receive computers.
- No unencrypted authentication
- Authentication of laptops or users will not depend upon identifiers that are sent unencrypted over the network. This means no cleartext passwords of any kind will be used in any OLPC protocol and Ethernet MAC addresses will never be used for authentication.
- Out-of-the-box security
- The laptop should be both usable and secure out-of-the-box, without the need to download security updates when at all possible.
- Limited institutional PKI
- The laptop will be supplied with public keys from OLPC and the country or regional authority (e.g. the ministry or department of education), but these keys will not be used to validate the identity of laptop users. The sole purpose of these keys will be to verify the integrity of bundled software and content. Users will be identified through an organically-grown PKI without a certified chain of trust — in other words, our approach to PKI is KCM, or key continuity management.
- No permanent data loss
- Information on the laptop will be replicated to some centralized storage place so that the student can recover it in the event that the laptop is lost, stolen or destroyed.
If this subject matter interests you, please read the complete Bitfrost specification, join the OLPC security mailing list, share your thoughts, and join the discussion.