1

When you trust a GnuPG key, you can choose one of these five options (and I'm assuming the same options exist in other OpenPGP tools):

1 = I don't know or won't say (undefined)
2 = I do NOT trust (never)
3 = I trust marginally
4 = I trust fully
5 = I trust ultimately

However, there is a "sixth" option that doesn't show up in the list: if you haven't yet set trust for a key, it shows up as unknown.

Is there a reason GnuPG makes a distinction between the two? Is undefined trust treated differently than unknown, or is the distinction just for personal reference?

  • 1
    Unknown means you've never seen the cert before. Undefined means you've seen it, recognized it, and gave it the lowest trust level. – RoraΖ Oct 6 '14 at 16:37
  • @raz I thought never was the lowest trust level. – IQAndreas Oct 6 '14 at 19:14
2

The options 2 to 5 (never, marginally, fully and ultimately trusted) correspond to a definite decision made by you on the trust level which influences validity calculation.

Unknown says, you haven't made any decision at all and thus is special, indicating no value at all (you might consider it some kind of NULL value). Option 1, undefined is similar and has similar outcome regarding validity caluclation, but is a statement you can issue on not wanting to decide on the key's trust level. You might want to use it as future reference instead of not setting any trust value.

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