不可否认性是重复的吗？
当我们谈论安全性时，我们有以下要求：
- 身份验证
- 完整性
- 不可否认性
前两个要求中是否包含第三个要求？ 如果我们知道A发送了消息（身份验证）并且自A发送消息以来消息没有被更改（完整性），那么A如何拒绝发送它？
请不要谈论 dig-sig，因为它是技术层面的。 我说的是业务需求。
When we talk about security we have the following requirements:
- authentication
- integrity
- Non-repudiation
Isn't the third requirement included in the first two? If we know A sent the message (authentication) and it has not been changed since A sent it (integrity) then how can A repudiate sending it?
Please don't talk about dig-sig as it's in the technical level. I'm talking about the business requirements.
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身份验证和完整性保护都无法防止重放攻击。 恶意用户可以捕获经过签名和加密的消息并多次发布。 因此，一方可以否认已多次发送同一消息。
使用时间戳和/或随机数使每条消息唯一可以解决这个问题，因此与签名和加密结合使用可实现不可否认性。
Neither authentication nor integrity protections prevent replay attacks. A malicious user can capture a signed and encrypted message and post it multiple times. Therefore a party can repudiate having sent the same message multiple times.
Making each message unique using timestamps and/or nonces addresses this and is therefore used for non-repudiation in combination with signing and encryption.
不可否认性与完整性和身份验证不同，因为它意味着发送者对消息的内容负责。
有许多系统使用密钥来进行身份验证和完整性，但经过身份验证的内容没有任何意义。 例如，假设为了在我的系统上对您进行身份验证，我发送了一个不可预测的质询，并要求您对其进行签名并将其发回。 如果签名有效，我相信您知道一些秘密，因此就是您所声称的身份。 我要求您用于签署这些质询的密钥指定用于数字签名，但不一定用于不可否认性。
现在假设我没有选择随机挑战，而是尝试通过发送挑战来欺骗您：“我将向埃里克森支付一百万美元。” 如果你的系统签名了，我可以索赔一百万美元吗？ 签名的消息是真实的且未被篡改，但除非您使用标记为不可否认的密钥对其进行签名（例如，在 X.509 证书的密钥使用扩展中设置此标志），否则您可以否认您知道其内容并拒绝我的主张。
不可否认性对于诸如商业交易中的文件签名之类的事情是有意义的——在这种情况下，您有义务采取某些行动或付款。
Non-repudiation is different than integrity and authentication because it implies that the sender is accountable for the contents of a message.
There are many systems that use a key for authentication and integrity, but the authenticated content doesn't mean anything. For example, suppose that in order to authenticate you on my system, I send an unpredictable challenge and ask you sign it and send it back. If the signature is valid, I trust that you know some secret and therefore are who you claim to be. I'd require the key you use for signing these challenges to be designated for digital signatures, but not necessarily for non-repudiation.
Now suppose instead of choosing a random challenge, I try to trick you by sending the challenge, "I will pay erickson one million dollars." If your system signs that, do I have a claim to a million dollars? The signed message is authentic and not tampered with, but unless you signed it with a key flagged for non-repudiation (for example, setting this flag in the key usage extension of an X.509 certificate), you can deny that you were aware of its content and reject my claim.
Non-repudiation makes sense for things like a signatures on documents in a business transaction—cases where you are obligating yourself to some action or payment.
通过身份验证和完整性，您可以实现消息的真实性，即。 收件人可以确信发件人 ID 和消息内容是真实的。
另一方面，不可否认性确保相关方没有可以否认已发送或接收消息。 在前面的方案中：
因此，不可否认系统将包括某种确认以提供这些证明。
With authentication and integrity, what you can achieve is message authenticity, ie. the recipient can be confident that the sender ID and message content are genuine.
Non-repudiation, on the other side, ensures that none of the involved party can deny having sent or received the message. In the previous scheme:
Non-repudiation systems will therefore include some kind of acknowledgment in order to provide these proofs.
通常这三个安全要求是CIA，即
Confidentiality
正直
真实性
但是关于不可否认性，身份验证和完整性不一定提供不可否认性，因为完整性表示某些消息在从点传输到 Y 时没有改变。
身份验证可以告诉您某些消息是由了解某些（共享）秘密的任何人发送的，而这些秘密应该只有一个人知道。
想象一下病毒窃取了 Alice 的私钥，在这种情况下，您可以获得消息 X 的完整性并验证该消息来自 Alice（尽管有人可能会争论这是否是真正的身份验证），但是，一些窃听者使用窃取的私钥来发送信息。
Usually the three security requirements are CIA, i.e.
Confidentiallity
Integrity
Authenticity
But concerning non-repudiation, authentication and integrity dont necessarily provide non-repudiation since integrity says some message has not changed when traveling from point X to Y.
Authentication can tell you that some message is sent by anybody who has knowlegde of some (shared) secret that should be only known to a person.
Imaginge a virus stealing private keys from Alice, in that case you can have integrity of message X and authentication that the message is from Alice (although one can argue if this is real authentication) however, some eavesdropped used the stolen private key to send the message.