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seen Mar 17 at 11:26

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
10
comment What are the differences between a digital signature, a MAC and a hash?
@PaĆ­loEbermann: that's perfect, thanks! Your edit was substantial so I enabled "community wiki" on my answer, it's only fair.
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 @PaĆ­loEbermann! 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
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
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.
Dec
9
comment Can I use PGP to sign a message without providing cryptographic non-repudation?
Is there any way using asymmetric encryption that you can achieve what a MAC achieves: authentication without non-repudiation?
Dec
9
comment Can I use PGP to sign a message without providing cryptographic non-repudation?
You don't have to publish your private key to remove non-repudiation, you can simply use a MAC. See this