[tor-bugs] #17021 [Website]: Update FAQ entry about identity keys to mention ed25519 keys.

[Tor Bug Tracker & Wiki]

#17021: Update FAQ entry about identity keys to mention ed25519 keys.
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     Reporter:  nickm    |      Owner:  Sebastian
         Type:  defect   |     Status:  new
     Priority:  normal   |  Milestone:  Tor: 0.2.7.x-final
    Component:  Website  |    Version:
   Resolution:           |   Keywords:  ed25519 TorCoreTeam201509
Actual Points:           |  Parent ID:
       Points:           |    Sponsor:
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Comment (by s7r):

 Hello Sebastian,

 A suggestion for the faq. Please edit if you think it doesn't read right -
 I speak better English than I write when it comes to explaining things.
 Wanted the text to be as simple as possible and make sense for almost
 anyone.

 In the current FAQ I only found one question related to relay identity
 keys:

 '''I want to upgrade/move my relay. How do I keep the same key?'''

 I recommend replacing the answer with this:

 '''When upgrading your Tor relay, or moving it on a different computer,
 the important part is to keep the same identity keys (stored in
 "keys/ed25519_master_id_secret_key" and "keys/secret_id_key" in your
 DataDirectory). It is important to keep backups of the identity keys so
 you can restore a relay in the future in case you need to re-install -
 this way the reputation of the relay won't be wasted.'''

 '''This means that if you're upgrading your Tor relay and you keep the
 same torrc and the same DataDirectory, then the upgrade should just work
 and your relay will keep using the same key. If you need to pick a new
 DataDirectory, be sure to copy your old keys/ed25519_master_id_secret_key
 and keys/secret_id_key over.'''

 '''*Note: As of Tor 0.2.7 we are using new generation identities for
 relays based on ed25519 elliptic curve cryptography. Eventually they will
 replace the old RSA identities, but that will happen in time, to ensure
 compatibility with older versions. Until then, each relay will have both
 an ed25519 identity (identity key file: keys/ed25519_master_id_secret_key)
 and a RSA identity (identity key file: keys/secret_id_key). You need to
 copy / backup both of them in order to restore your relay, change your
 DataDirectory or migrate the relay on a new computer.'''


 And add a new question:
 '''How do offline ed25519 identity keys work? What do I need to know?'''

 This feature is optional, you don't need to use it unless you want to. If
 you want your relay to run unattended for longer time without having to
 manually do the medium term signing key renewal on regular basis, best to
 leave the master identity secret key in DataDirectory/keys, just make a
 backup in case you'll need to move or reinstall it.

 As of Tor 0.2.7 offline ed25519 identity keys are supported. In simple
 words, it works like this:
 - there is a master ed25519 identity secret key file named
 "ed25519_master_id_secret_key". This is the most important one, so make
 sure you keep a backup in a secure place - the file is sensitive and
 should be protected. Tor could encrypt it for you if you generate it
 manually and enter a password when asked. If you know this file has been
 compromised, you have to generate a new identity and start a fresh relay
 with no reputation.

 - a medium term signing key named "ed25519_signing_secret_key" is
 generated for Tor to use. Also, a certificate is generated named
 "ed25519_signing_cert" which is signed by the offline master key and
 confirms that the medium term signing key is valid for a certain period of
 time. The default validity is 30 days, but this can be customized by
 setting "SigningKeyLifetime N days|weeks|months" in torrc.

 - there is also a master public key named "ed25519_master_id_public_key,
 which is the actual identity of the relay advertised in the network. This
 one is not sensitive and can be easily computed from
 "ed5519_master_id_secret_key".

 Tor will only need the medium term signing key and certificate as long as
 they are valid, so the master identity secret key can be kept outside
 DataDirectory/keys, on a storage media or a different computer.

 ''If you want to use this feature, we have a guide about how to use and
 manage offline ed25519 identity keys. Click here to read it.'' - this will
 be a link to a full long guide, which I will write - subject of ticket
 #16645. Most probably we will include the same link in the manual and
 maybe other places as well.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17021#comment:3>
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