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-----BEGIN PGP SIGNED MESSAGE----- |
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Hash: SHA1 |
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On 03/27/2011 08:13 PM, Robin H. Johnson wrote: |
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> On Sat, Mar 26, 2011 at 10:12:10AM +0100, Andreas K. Huettel wrote: |
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>> 3) Rely on an existing key list somewhere distributed in portage; the list |
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>> file with the key id's (not the keys themselves) is signed with a master key. |
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>> Is a mediocre and potentially insecure workaround. |
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>> Pros: you can exactly decide what keys are used and trusted, without thinking |
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>> about GnuPG's inner workings. A user can edit his key and the key remains |
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>> trusted. |
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>> Cons: Mainly that the key id is a pretty short hash afaik.(Any better-informed |
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>> people around?) |
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> 1. Generate said list L from the GPG fields in LDAP (w/ long-form keyids) |
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> 2. Clear-sign L, produces L' |
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> 3. Include L' in /metadata/ during rsync content build. |
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> 3.1. Provide all L' files in a trusted Git repository for historical reference. |
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> 4. Tree-sign per GLEP58, such that signed list is included. |
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> |
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> Pros: |
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> - L' is plaintext and works well w/ rsync deltas. |
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> |
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> Security weakpoints: |
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> - Introduces new weak point if attacker can compromise the automated |
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> clear-signing service of #2. |
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> |
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>> 4) Rely on an existing list of keys somewhere distributed in portage and |
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>> possibly somewhere else (keyservers); a key userid is signed with a master |
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>> key. Work with GnuPG's well-tested and well-thought-out trust relationships. |
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>> Back to start, time to re-read the entire thread... :) |
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> What does this actually add over #3 in terms of security? |
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> |
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|
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This is an extremely non-trivial question. You're talking about signing |
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each individual key's fingerprint vs generating a list of key |
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fingerprints (hashes of the key), concatenating them all, hashing THAT, |
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and then signing that hash. |
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|
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- From a cryptologic point of view, I would be *extremely* impressed with |
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anyone that can find a proof of security that shows that those two are |
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equivalent. |
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|
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Simple(ish) example. By creating a list you're introducing a lot of data |
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that is then getting hashed. Now, from a cryptologic point of view, I |
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would *not* attack the signature per se, but rather the underlying hash |
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of the list. By providing a large file with lots of data, there are |
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attacks against (some) has functions that can make use of this (Small |
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changes in the file that will result in the same hash with probability |
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greater than normal). (Anyone know off the cuff what hash is actually |
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used?) |
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|
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Now, the other method would require having to single out each hash on |
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it's own, and the underlying key that it hashed. That data is harder to |
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deal with because you have to manipulate one key into another *valid* |
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key(a difficult task to have it still be valid) and have it come out |
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with the same hash. Whereas with the file, who cares if they invalidate |
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another key, as long as they can get their hash into the file and have |
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the hash for the sig come out the same. |
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|
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Point being, what it adds / subtracts is not a simple question. Crypto |
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is a funny beast, and is best not trifled with unless you understand the |
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underlying math / the current attacks etc (And even then, don't do it |
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=P). Do I think that using #4 gives us a huge difference over #3, even |
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with my years of study on this topic I would not even begin to try to |
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answer that. Chances are the difference is negligible for our *needs* |
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(see below), but I don't think it's negligible in the true sense of |
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security. |
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|
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Having said that we aren't exactly talking about securing the end all be |
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all. We just want to be able to verify with a reasonable degree of |
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certainty that the tree is in a good state and that it wasn't tampered |
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with. Do we really need the end all be all, I somehow doubt it. |
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|
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- -- |
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Dane Smith (c1pher) |
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Gentoo Linux Developer -- QA / Crypto / Sunrise / x86 |
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RSA Key: http://pgp.mit.edu:11371/pks/lookup?search=0x0C2E1531&op=index |
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-----BEGIN PGP SIGNATURE----- |
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Version: GnuPG v2.0.17 (GNU/Linux) |
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Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ |
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|
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iQIcBAEBAgAGBQJNkLnkAAoJEEsurZwMLhUxV64P/1AbiEkcbouFd/XZ50aq/BsC |
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LRjlUC5GbCpBL1MBTigP1OWO0HT8JvBEKJPAbwChr+KSQqtk3/HOcaoRTlJDz3hf |
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MViWW4bBB1PQq4XL5in58JH2ohQBx49+RgeovdREnTWFJlDsHbxIZN3JTV8EHq7a |
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8xpni/uPLCbW3XGS2G3x/L7f8yPJOqEyTPROU3s+YGDtZkDYwDI1bn+k2Fnu+3a7 |
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kkFyp4aRrajiFE4WK20iBnnPJn1knfR47O6UEP4aZu/GCC3s/3fJP5pVNlnla7mU |
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5RXJ1j6Tj3MQoCBdbGypEaVYJf1ZiJGdpUYOHpi4XL2R3mh8XsmnEF53pdp7GOk/ |
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wHfuKvvZ5uKtYawj8QhVB8+Y97kTNYc7t7OIShpAZb0SoyUN+ZGoal4pDASkSM15 |
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uATdmilb7z5JIEKiQ0lLwjdLjJJq5imgpB4YuQBqiF3sKmH8N9Qf5+kCRxvSE09y |
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lq1hWqppGX+H4CvA5FPRkB7/Qvg2prmwfdIqDlGWfMlR2KLsFoIzRyjKnL1xSCgn |
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eX/hTD9umMkzOho7l1eL |
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=h4nm |
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-----END PGP SIGNATURE----- |
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