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认证协议
认证证明消息是新鲜的且来自其声称的一方，而新鲜性是其中微妙的一半：时间戳需要同步的时钟，而时钟本身就是攻击目标；一次性随机数需要记住曾经使用过的每个值；挑战-响应协议通过让验证者实时选择一次性随机数来结合两者。公钥协议则从签名的时间戳和一次性随机数构建双向认证，会话密钥在对方的公钥下传送；而私钥协议通过 KDC 运行，「Needham-Schroeder」使用一次性随机数来确保新鲜性，并用票据作为 KDC 的签名介绍；「Kerberos」将这一设计产品化，主密钥从密码派生。所有这些协议中的每条消息都至关重要，因为历史上的认证漏洞都是遗漏——缺失名称、重用一次性随机数——这些漏洞导致了重放和冒充。
1. Freshness First
Freshness First
2. Proving It Both Ways With Public Keys
Proving It Both Ways With Public Keys
3. The KDC in the Middle
The KDC in the Middle
4. Reading a Protocol Like an Auditor
Reading a Protocol Like an Auditor
5. The recorded login
An attacker records a correctly signed login message and replays it the next day. What property did the protocol fail to enforce?
6. Two weaknesses, one fix
Why do practical protocols combine timestamps and nonces?
7. The live proof
In challenge-response, why does the verifier generate the nonce itself?
8. The load-bearing field
A signed authentication message omits the intended recipient's identity. What attack opens?
9. The ticket as signature
In Needham-Schroeder, why does the ticket function as a signed statement from the KDC?
10. Kerberos's root
What does Kerberos derive each user's master key from, and what weakness follows?
11. The used-once value
What is a random value included in a message to guarantee it has never been used before called?
12. The live exchange
What protocol shape has the verifier mint a fresh value and demand the prover sign or encrypt it, proving the reply was made now?
13. The canonical trio
Which classic secret-key authentication protocol runs Alice, Bob, and a KDC through nonces and a ticket, and what system productized it?
14. The recorded attack
What class of attack re-sends a previously recorded genuine message to gain entry?