| English | 意味 |
|---|---|
| TLS/ˌtiː el ˈes/ | 転送層セキュリティ |
| digital certificate/ˈdɪdʒɪtl səˈtɪfɪkət/ | デジタル証明書 |
| digital signature/ˈdɪdʒɪtl ˈsɪɡnɪtʃə/ | デジタルサイン |
| authenticity/ɔːθənˈtɪsɪti/ | 真正性 |
| integrity/ɪnˈteɡrɪti/ | 完全性 |
| Certificate Authority/səˈtɪfɪkət əˈθɒrɪti/ | 証明書発行機関 |
Encryption alone would not have helped
- Suppose your connection to your bank is perfectly encrypted, and suppose an attacker sits between you and the bank, holding an encrypted connection to each side.
- Every byte is encrypted. Every byte is also read, and changed, by the attacker. Encryption did exactly what it promised and protected nothing that mattered.
- What was missing was not secrecy but identity: proof that the public key you encrypted to belongs to the bank and not to whoever answered.
- This lesson is the three things that close that gap: TLS 传输层安全 for the connection, a digital certificate 数字证书 for identity, and a digital signature 数字签名 for authenticity and integrity.
What TLS provides
- TLS, Transport Layer Security, the successor to SSL, is the protocol that secures data in transit. It provides three things together, and the exam wants all three named.
- Encryption, so an eavesdropper reads only ciphertext. Authentication, so the client knows which server it is talking to. Integrity 完整性, so any tampering in transit is detected.
- It is what the padlock in a browser means, and it is used by HTTPS, secure email, VPNs and online banking.
TLSは、送信中のデータに対してどの組み合わせの保護を提供するか？
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TLSは通信を暗号化し、証明書を通じてサーバーを認証し、改ざんを検知（整合性）する。
TLSが送信中のデータに提供する保護はどれか？すべて該当するものを選択してください。
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
配送はTCPの役割である。TLSはその上に機密性、識別、改ざん検知を追加する。
The handshake
- The client proposes the cipher suites it supports. The server replies with its choice and its digital certificate, which contains its public key.
- The client checks the certificate. If it is satisfied, the two sides use asymmetric encryption to agree a fresh session key.
- All subsequent traffic is encrypted symmetrically with that session key: fast, and freshly keyed for this one conversation.
- The certificate check is the step that defeats the attack in the hook. Without it, the client would happily agree a session key with the attacker.
Asymmetric to agree the key, symmetric for everything after
TLS ハンデシェイク
ロックアイコンが表示される前に何が起こるかを確認します。スローな公開鍵暗号は共有鍵の合意にのみ使われ、実際のページデータは高速な対称暗号によって保護されます。
TLS ハンデシェイクの手順を正しい順序に並べ替えてください。
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鍵の合意よりも先に証明書検証が行われることが、ミドルマン攻撃を防ぐ要因です。
Digital certificates
- A digital certificate binds an identity, a domain or organisation, to a public key, and is signed by a trusted Certificate Authority 证书颁发机构 (CA).
- It contains the subject whose identity it certifies, the subject's public key, the issuer, a validity period, and the CA's digital signature over all of it.
- The signature is what makes it trustworthy: anyone can create a document claiming to be a bank, but only the CA can produce a signature that verifies with the CA's public key.
A trusted third party vouches that this key belongs to this name
各セキュリティメカニズムとそれぞれの機能にマッチングさせてください。
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証明書は公開鍵の保証を行い、署名は秘密鍵を用いて送信者とその内容の未変更性を証明する。
Worked example: how a client verifies a certificate
- Describe the checks a browser makes on a website's digital certificate. [4]
- It checks the certificate is within its validity period, neither expired nor not yet valid.
- It checks the subject name matches the domain the user asked for, which is the check that catches an attacker presenting a genuine certificate for a different site.
- It verifies the CA's signature on the certificate using the CA's public key, proving the certificate has not been altered.
- It follows the chain to a root CA the browser already trusts. If any check fails, the browser shows the "connection is not private" warning.
証明書の検証時、クライアントはそれが以下であることを確認する：
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ブラウザは有効期限、対象名（Subject Name）がサイトと一致すること、そして信頼できるルートCAまでのCA署名を確認する。
デジタル証明書の信頼性の根拠は何か？
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銀行を装った文書を作成して鍵を載せることは誰でもできる。しかし、CAの公開鍵で検証できる署名を作成できるのはCAのみである。
Digital signatures
- A digital signature proves authenticity 真实性, who sent the message, and integrity, that it was not changed. It does not encrypt the message or make it secret.
- To sign: the sender puts the message through a hash function to produce a digest, then encrypts that digest with their own private key. The encrypted digest is the signature, and it travels with the message.
- To verify: the receiver decrypts the signature with the sender's public key to recover the digest, hashes the received message themselves, and compares the two.
- If they match, only the holder of the private key could have made the signature (authenticity) and the message cannot have changed (integrity), since any change would produce a different hash.
Sign the digest with the private key, check it with the public key
デジタル署名を作成するために、送信者は：
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署名とは、メッセージをハッシュ化してから、そのダイジェストを秘密鍵で暗号化することである。受信者は公開鍵で検証する。
デジタル署名は真正性と整合性を証明する（誰が署名したか、内容が変更されていないか）が、メッセージ自体を隠すわけではない。機密性を確保するには暗号化も必要である。
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署名と暗号化は別々の目的を持つ：署名は起源と整合性を証明し、暗号化は内容の機密性を保つ。
メッセージに署名するためには、送信者は自身の____でダイジェストを暗号化する。
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受信者はその後、送信者の公開鍵で復号する。この方法で署名を開くことができるのは、秘密鍵の保有者だけである。
Worked example: why the keys are the other way round
- In confidential messaging the sender uses the recipient's public key. In signing, the sender uses their own private key. Explain why.
- For confidentiality you want only one person to be able to read it, so you lock with the key everyone has and it opens only with the one key nobody else has.
- For a signature you want everyone to be able to check it and only you to be able to produce it, so you lock with the key only you have and it opens with the key everyone has.
- The direction of the key pair follows from what you are trying to prove. This is the single most tested idea in the topic.
単に接続を暗号化だけでは、ミドルマン攻撃を完全に防ぐことはできない。
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暗号化は、通信の向こう側の誰かにとってチャネルを保護します。証明書はその人物が誰であるかを証明するものであり、そのため検証が重要な役割を果たしています。
Acquiring a certificate
- The server owner generates a key pair and sends the public key and identity details to a Certificate Authority. The private key stays with the owner. The CA checks control of the domain or the identity required by the certificate type.
- The CA signs a certificate binding that identity to the public key, using the CA's private key, and returns it for installation. A certificate is public evidence about a key, not a container for the owner's secret key.
CAへの証明書請求に含まれるべき項目はどれか。すべて選択すること。
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CAは主張された識別情報を確認し、公開鍵と紐付ける。申請者の秘密鍵は秘匿されたままとなる。
デジタル証明書の取得手順を順序立てて記述せよ。
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CAが紐付けに署名する前にIDが検証される。サーバーはクライアントに対して証明書を提示する。
Worked example: whose key signs what?
- A software publisher signs a download with the publisher's private key. The receiver obtains the publisher's public key from a valid certificate and uses it to verify the download signature.
- The CA's private key signs the certificate; the publisher's private key signs the download. A valid certificate establishes whose public key to trust. It does not itself sign the program or prove the program is harmless.
各操作を対応する正しい鍵にマッチさせよ。
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CAがIDと鍵の紐付けを保証する。公開者は自身のコンテンツに署名し、受信者は対応する公開鍵で確認を行う。
Marks that slip away
- TLS provides encryption, authentication and integrity. Naming only encryption loses two-thirds of the answer.
- A signature encrypts the hash of the message with the sender's private key, not the message itself, and it does not make the message secret.
- Verifying a certificate means the dates, the name matching the domain, the CA's signature and the chain to a trusted root. The name check is the one candidates forget.
- The certificate is what stops a man-in-the-middle. Encryption on its own does not: it protects a channel to whoever is at the other end.
You've got it
- TLS gives encryption, authentication and integrity; its handshake presents a certificate, then agrees a session key for fast symmetric encryption
- a digital certificate binds an identity to a public key and is signed by a Certificate Authority; it carries the subject, its public key, the issuer, the validity period and the CA's signature
- verify a certificate by the dates, the name matching the domain, the CA's signature and the chain to a trusted root
- a digital signature is the message's hash encrypted with the sender's private key, checked with the sender's public key: it proves authenticity and integrity, not confidentiality