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How does a signing a post with a pgp key prove that you are actually the person behind the post? (lemmy.nz)

submitted 1 year ago by Fizz@lemmy.nz to c/askscience@lemmy.world

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I saw that people on the dark web would sign their posts with a PGP key to prove that their account has not been compromised. I think I understand the concept of how private and public keys work but I must be missing something because I don't see how it proves anything.

I created a key and ran gpg --export --armor fizz@... and I ran that twice and both blocks were identical. If I posted my public key block couldn't someone copy and paste that under their message and claim to be me?

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[–] sotolf@programming.dev 3 points 1 year ago (1 children)

So they are not excrypting it, but do we agree that with signatures the author uses their private key + the clear message to generate "something"?

Yeah sure, and I think the person you are arguing with is saying as much as well, it's just that this is not encrypting it, when you encrypt something you obfuscate it in a way that is possible to deobfuscate, think the caesar cipher as a simple encryption, a hash/signature on the other hand is something that is generated from the clear text using your private key, which is not possible to decrypt, think very simplified that the person would just put the amount of each letter of the alphabet used in in the text, then add the length of the thread, and then multiplied by your private key. This way it's proven that the holder of the private key is the person writing the text, and that the text hasn't changed since the signature was generated.

... so then anyone can use the author's public key to check that "something" against the clear mesage to confirm the author's identity?

They can confirm that the person holding the private key (not identity, just that they have the key) and also that nobody changed it since they signed it (like the person adminning the forum or a moderator or something)

If that's the case, then my error is that the operation to generate the signature is not an encryption. So, may I ask... what is it? A special type of hash?

It's basically a hashing function yeah.

[–] Crul@lemmy.world 2 points 1 year ago

Thanks, now it's clear.

I corrected my original comment.