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I'm looking at the event description for the key-signing party at an upcoming BSD conference, and it's mentioned that I shouldn't bring my computer in to the event:

Things to bring

  • no computer

What risks does bringing a computer into a key-signing party pose?

  • More specifically, wouldn't someone need to bring a computer to actually generate the hashes? At least, in Little Brother there is one laptop involved. – KlaymenDK Jun 9 '16 at 7:42
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    Also, no tequila – UniversallyUniqueID Jun 9 '16 at 9:15
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    Sure you are not being invited to some kind of swinger event? Key parties with no computers involved do exist, you know. – Damon Jun 9 '16 at 10:01
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    Definitely don't bring an electric monk. Those damn things are a pain. – Max Vernon Jun 9 '16 at 17:03
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Quote from Wikipedia:

Although PGP keys are generally used with personal computers for Internet-related applications, key signing parties themselves generally do not involve computers, since that would give adversaries increased opportunities for subterfuge. Rather, participants write down a string of letters and numbers, called a public key fingerprint, which represents their key. The fingerprint is created by a cryptographic hash function, which condenses the public key down to a string which is shorter and more manageable. Participants exchange these fingerprints as they verify each other's identification. Then, after the party, they obtain the public keys corresponding to the fingerprints they received and digitally sign them.

another one from openwest:

If you bring a computer, please keep it in your bag and powered down during the party. This is for security measures to prevent the spread of malicious software, the misplacement of private keys, and damaged or misplaced equipment.

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    A likely scenario is someone brings a thumb drive with malicious tools, looks for someone with a laptop, and says, here, just plug in my thumb drive and I'll share my key! – Mark Stewart Jun 9 '16 at 14:07
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    Wait, you don't actually sign keys at a key-signing party? You just arrange to sign them later? Weird. – user2357112 Jun 9 '16 at 16:19
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    @user2357112 the hard part, which requires people to be in a single room or such, is to verify the person (checking a ID card or something), the actual digital signing can be done by everybody alone easily at some other time. – johannes Jun 9 '16 at 18:48
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    @johannes So you are to completely 100% trust total strangers that just happen to produce a sort-of-real-ish looking ID? The ID could be faked, the person could be a mal-actor, etc. I don't see how it's possible to establish a reasonable line of trust after just meeting someone for a few minutes. Especially after you start to trust people whom your trustees trust (vouched for)... seems like an easy way into the "circle" if your up to no good. Seems like these "key signing parties" are really just good excuses to drink! (nothing wrong with that by itself) – SnakeDoc Jun 10 '16 at 14:47
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    @SnakeDoc this depends on the exact setting. On my local usergroup with a fixed set of regular participants this is less of an issue compared to an international conference with participant from all over the world, which don't know each other with different sorts of ids. Anyways, I just commented on the "no computer" part. – johannes Jun 10 '16 at 23:26
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Firstly, that statement doesn't mean "don't bring a computer"; it means " you don't need to bring a computer". Many people going to their first key signing party are likely to assume that, since the keys are intended for use on computers, they will need to bring a computer containing their keys, signatures, or encryption software. What actually happens is that the verification of the keys takes place using key fingerprints without any computers and is entered into an online database after the event from participants' own computers at home.

Secondly, as a computer is not used at the key signing party, it is generally discouraged to take a computer to a key signing party. Having unnecessary computers at an event of that kind is a large security risk, as a malicious participant could use another participant's computer to sign his own key with the other participant's signature, or he could even steal other people's private keys or distribute malware. In short, computers are not necessary at key signing parties and having them present would introduce all the security risks that computers inherently bring with them, which is never a good idea when those computers are likely to contain private encryption keys, so most key signing parties prefer participants to write public key fingerprints on paper and keep their private keys safely at home.

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It is a matter of speed and convenience, for the most part.

Your basic options for signing a key:

  1. Both participants set up their computers next to each other, one reads off their fingerprint, the other verifies at the same time, then the key is signed immediately.

  2. One participant shows their computer screen with the fingerprint to the other, who writes down the fingerprint.

  3. The signee hands over a small piece of paper along with their photo ID, and the signer keeps the paper.

It is obvious to see that method 3 is way faster than the other two. By asking people to not bring computers, they are implicitly asked to bring enough copies of their key, or to register beforehand so they can distribute a list of fingerprints (you will need to verify that the key in the file is yours, and they will read a checksum of the file in the beginning).

Shameless plug: If you have only ASCII characters in your name, the gpg-key2ps script may be helpful to you -- it is always a good idea to have a few keyslips in your pocket.

  • Huh, that's interesting. Is there a standard format/system for using keyslips with an optional QR code version of the thing? – StarWeaver Jun 9 '16 at 22:15
  • @StarWeaver, no, because basically the tool needs to be rewritten from scratch -- it started as a sed script and has grown some additional code around to make it valid perl. For Unicode, picture UID or QR code support, we'd really need C++ and Pango+Cairo or something such. – Simon Richter Jun 9 '16 at 23:15
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    An optional QR code sounds like a horrible idea. I can just put another key in the QR code and hope that you'll sign that without double checking that both are identical. And since you have to double check anyway, the QR code offers no advantage. – pipe Jun 9 '16 at 23:31
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    @pipe, the keyslips are prepared by the signee, who has an interest that the signer receives the correct key. The signer only verifies that the information in any UID they sign matches the documents provided. – Simon Richter Jun 9 '16 at 23:37
  • @SimonRichter Why do you say the signee has an interest that the signer receives the correct key? Getting widely-trusted signers to sign the wrong keys can be of great use. Aren't you supposed to confirm that the person whose ID you checked controls the corresponding private key before vouching for a key? (In the case of this key signing party, this check is done before the party by the host.) – David Schwartz Jun 10 '16 at 16:02

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