Flimm

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	176 reputation	bio	website	launchpad.net/~flimm	visits	member for	6 months
7 badges		location			seen	May 3 at 8:30

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Dec 13	accepted	What are the differences between a digital signature, a MAC and a hash?
Dec 12	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? If the sender uses a one-time signing key, how would this provide authentication at all? How would the recipient know that the one-time signing key is associated with the sender's validated master signing key?
Dec 12	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? If understand correctly, an MDC provides some level of integrity, but not authentication. After all, even with an MDC, an attacker could just use the recipient's public key to create a new encrypted message. What I'm asking for is authentication without non-repudiation. I realise the non-repudiation OpenPGP offers isn't good enough for court, but it could be good enough for another OpenPGP user.
Dec 12	awarded	Critic
Dec 11	awarded	Self-Learner
Dec 10	comment	What are the differences between a digital signature, a MAC and a hash? @PaŭloEbermann: that's perfect, thanks! Your edit was substantial so I enabled "community wiki" on my answer, it's only fair.
Dec 10	awarded	Teacher
Dec 10	comment	What are the differences between a digital signature, a MAC and a hash? Please go ahead and edit it to make it look less homework, I'm not sure what I'm doing wrong so I'm not sure I can fix it. Thanks @PaŭloEbermann! I posted this question because I saw some users confuse these three primitives in this question, and I wanted a question like this to point to.
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? @AJ Henderson: you're right. Thanks for the explanation!
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? @AJ Henderson - That would provide non-repudiation, which is an undesired property. The recipient can pass `Encrypt(symmetric_key, (message, mac))` and `Encrypt(public_key, Sign(private_key, symmetric_key))` to a third party, and the third party can be confident the message originated from the sender, since the recipient could not have forged it.
Dec 10	awarded	Commentator
Dec 10	comment	What are the differences between a digital signature, a MAC and a hash? Why am I being downvoted? It's not homework, and any way, homework questions are allowed.
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? Your solution would be to pass `Encrypt(symmetric_key, (message, mac))` and `Encrypt(public_key, symmetric_key)` to the recipient. How does this provide authentication? Surely, any attacker could form this pair of cipher-texts.
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? Someone deleted my comment.
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? That's what I want to find out.
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? Yes, there is a difference between authentication and non-repudiation.
Dec 10	answered	What are the differences between a digital signature, a MAC and a hash?
Dec 10	asked	What are the differences between a digital signature, a MAC and a hash?
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? I downvoted this answer, because it does not distinguish correctly between a digital signature, a MAC and a hash.
Dec 10	comment	Can I use PGP to sign a message without providing cryptographic non-repudation? A digital signature proves that the message has been signed by the holder of the signature key, this proof can be passed to a third party, such as a judge. A MAC proves that the message has been signed by either the sender or the recipient, the recipient can not pass it to a third party to prove that the sender signed the message, since the recipient could also have generated the MAC. A hash proves that the message has not been modified assuming that the hash has not been modified, but it does not provide authentication, since anyone can create a hash.