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Add a description of our new change process. Assign statuses to existing proposals. svn:r9461
67 lines
3.1 KiB
Plaintext
67 lines
3.1 KiB
Plaintext
Filename: 103-multilevel-keys.txt
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Title: Splitting identity key from regularly used signing key.
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Version: $Revision$
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Last-Modified: $Date$
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Author: Nick Mathewson
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Created:
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Status: Open
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Overview:
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This document proposes a change in the way identity keys are used, so that
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highly sensitive keys can be password-protected and seldom loaded into RAM.
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It presents options; it is not yet a complete proposal.
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Proposal:
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Replacing a directory authority's identity key in the event of a compromise
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would be tremendously annoying. We'd need to tell every client to switch
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their configuration, or update to a new version with an uploaded list. So
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long as some weren't upgraded, they'd be at risk from whoever had
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compromised the key.
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With this in mind, it's a shame that our current protocol forces us to
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store identity keys unencrypted in RAM. We need some kind of signing key
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stored unencrypted, since we need to generate new descriptors/directories
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and rotate link and onion keys regularly. (And since, of course, we can't
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ask server operators to be on-hand to enter a passphrase every time we
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want to rotate keys or sign a descriptor.)
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The obvious solution seems to be to have a signing-only key that lives
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indefinitely (months or longer) and signs descriptors and link keys, and a
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separate identity key that's used to sign the signing key. Tor servers
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could run in one of several modes:
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1. Identity key stored encrypted. You need to pick a passphrase when
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you enable this mode, and re-enter this passphrase every time you
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rotate the signing key.
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1'. Identity key stored separate. You save your identity key to a
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floppy, and use the floppy when you need to rotate the signing key.
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2. All keys stored unencrypted. In this case, we might not want to even
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*have* a separate signing key. (We'll need to support no-separate-
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signing-key mode anyway to keep old servers working.)
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3. All keys stored encrypted. You need to enter a passphrase to start
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Tor.
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(Of course, we might not want to implement all of these.)
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Case 1 is probably most usable and secure, if we assume that people don't
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forget their passphrases or lose their floppies. We could mitigate this a
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bit by encouraging people to PGP-encrypt their passphrases to themselves,
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or keep a cleartext copy of their secret key secret-split into a few
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pieces, or something like that.
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Migration presents another difficulty, especially with the authorities. If
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we use the current set of identity keys as the new identity keys, we're in
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the position of having sensitive keys that have been stored on
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media-of-dubious-encryption up to now. Also, we need to keep old clients
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(who will expect descriptors to be signed by the identity keys they know
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and love, and who will not understand signing keys) happy.
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I'd enumerate designs here, but I'm hoping that somebody will come up with
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a better one, so I'll try not to prejudice them with more ideas yet.
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Oh, and of course, we'll want to make sure that the keys are
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cross-certified. :)
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Ideas? -NM
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