3 ms·

How would one PGP sign their post that prevent malicious editing after the fact?

by talmand 10y ago

eli 10y ago
If someone else edited your post, the signature would no longer be valid. So the attacker could remove the signature or sign it with a different key or leave it alone and hope no one notices, but they couldn't re-sign with your key since they wouldn't have access to your private key file. Public key cryptography is really neat if you haven't played around with it before. I was being half-facetious, but if you want to be able to prove that a post is actually written by you, you probably want something like PGP.
- talmand 10y ago
  I still don't understand. If the edit left the public key as I left it, how would anyone know the difference? Are you meaning a feature of the site that let's you sign your post with your key as opposed to pasting your public key in the post?
  - eli 10y ago
    You don't just post your public key next to your comment, you use your private key to create a cryptographic signature of the contents of your post. Anyone with your public key can check that the signature is valid. Altering the text will cause that signature check to fail.
    - Nadya 10y ago
      The issue here is that almost nobody actually checks the signature. Some people edit their messages to invalidate them just to see if they'll get called out on it - they almost never are. So in theory, yes. But in practice - people are too lazy to validate or check the key (if the attacker replaces it with their own signed message) for every single post. This is a bigger issue the more users you have signing messages - as users begin getting lazier with checking each and every signed message. Unless they are under a lot of eyeballs from people who do care. If Wikileaks "signs" a message and it doesn't verify or wasn't with their key - a lot of people will call it out. If I "sign" a message or use a different private key (very possible that I sign with the wrong key when I have multiples) - I doubt anyone would call me out on it.

How would one PGP sign their post that prevent malicious editing after the fact?

by talmand 10y ago

How would one PGP sign their post that prevent malicious editing after the fact?

eli 10y ago

If someone else edited your post, the signature would no longer be valid. So the attacker could remove the signature or sign it with a different key or leave it alone and hope no one notices, but they couldn't re-sign with your key since they wouldn't have access to your private key file. Public key cryptography is really neat if you haven't played around with it before. I was being half-facetious, but if you want to be able to prove that a post is actually written by you, you probably want something like PGP.

talmand 10y ago
I still don't understand. If the edit left the public key as I left it, how would anyone know the difference? Are you meaning a feature of the site that let's you sign your post with your key as opposed to pasting your public key in the post?
- eli 10y ago
  You don't just post your public key next to your comment, you use your private key to create a cryptographic signature of the contents of your post. Anyone with your public key can check that the signature is valid. Altering the text will cause that signature check to fail.
  - Nadya 10y ago
    The issue here is that almost nobody actually checks the signature. Some people edit their messages to invalidate them just to see if they'll get called out on it - they almost never are. So in theory, yes. But in practice - people are too lazy to validate or check the key (if the attacker replaces it with their own signed message) for every single post. This is a bigger issue the more users you have signing messages - as users begin getting lazier with checking each and every signed message. Unless they are under a lot of eyeballs from people who do care. If Wikileaks "signs" a message and it doesn't verify or wasn't with their key - a lot of people will call it out. If I "sign" a message or use a different private key (very possible that I sign with the wrong key when I have multiples) - I doubt anyone would call me out on it.