本稿について
BlockStream開発のLiquid（Strong Federations）のホワイトペーパー、最終更新日: 2017/1/6時点のものを対象とします。本稿では「VIII. Conclusion」の日本語訳と「References」を掲載します。
原文はこちらになります。
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8. 結論
Bitcoinの高い評判はパーミッションレスなプルーフオブワークがインフラ開発に効果的なメカニズムであることを示しており、多数の企業全体で数億ドルものお金[59]がチップやネットワーク設計からデータセンタ管理、冷却システムまでにわたる新たなイノベーションに投資されている[60]。このリソースの集合体がもたらすセキュリティの価値は計り知れない。しかし、Bitcoinの基盤となっているプルーフオブワークには欠点がある[2]。つまり、皆で共有される台帳の現在のステートのための広く分散したチェックポイントを作るためにかかるレイテンシ（ブロックタイム）である。
本論文ではStrong Federationを紹介した。Strong Federationは連合化によるコンセンサスメカニズムで、プルーフオブワークと併せて利用すると現実世界の多くのシステム的なリスクを大幅に緩和する。このソリューションは具体的な実装決定とアタックサーフェスの最小化を通じて広いカテゴリの攻撃に対して耐性を持つ。Strong Federationはサイドチェーンテクノロジを活用してブロックチェーンテクノロジを改善する。さらに、秘匿アセット（Confidential Asset）やネーティブアセット（Native Asset）による機能改善が提案されている。いまのところHSM（ハードウェアセキュリティモデル）はブロックの署名が過去の署名と対立しない有効な履歴でのみ利用されていることを検証する限られた機能しか持たない。これはセキュアハードウェアのパフォーマンスの限界とHSMに組み込まれているものが変更不能であることの両方に起因し、複雑なルールセットのデプロイを困難でリスキーなものにしている。オーソライズされていないアップグレードの試みに対して堅牢でありながら、十分有力なアップグレードパスをHSMがサポートするには検証の改善が必要だ。別案として各ソフトウェアのデプロイが必然的に新しいハードウェアHSMのデプロイを含むようにするというものもあるが、これは高スト効率的ではない。
Strong Federationの初の実際に動く実装はLiquidである。LiquidはBitcoin交換とブローカレッジのマルチシグサイドチェーンで、そのセキュリティ特性を活用しながらBitcoin固有の制約を回避する。LiquidではBitcoinのSHA256ベースのプルーフオブワークはk-of-nのマルチシグスキームに置き換えられる。このモデルではコンセンサスの履歴がブロックチェーンであり、ブロックの署名は堅牢なプラットフォーム上で稼働する決定論的かつグローバルに分散したファンクショナリーセットにより、直接的に参加者のインセンティブを調整する方法で行われる。
Strong Federationは多くの汎用的な産業で役立つだろう。特に、管財や執行、取引の確定をコントロールする単一のパーティなしで電子的にアセットの代理人を務めたり交換を行うことを模索しており、なおかつセキュアかつプライベートに実施せねばならない業界では有用であろう。
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