Bug 2439

Summary: New sha256-base64 SSH Fingerprints in openssh-6.8
Product: Portable OpenSSH Reporter: Jakub Jelen <jjelen>
Component: MiscellaneousAssignee: Assigned to nobody <unassigned-bugs>
Status: CLOSED WONTFIX    
Severity: enhancement CC: djm
Priority: P5    
Version: 6.9p1   
Hardware: Other   
OS: Linux   
Bug Depends on:    
Bug Blocks: 2915    
Attachments:
Description Flags
Allow more fingerprint algorithms on client side none

Description Jakub Jelen 2015-08-06 00:26:32 AEST 
Based on our Fedora bug [1] I started investigation what is up to with the new Fingerprint hashes in openssh-6.8. I found one inconsistency and a usability problem.


 1) First of all manual pages mention that: 

> Valid options are: “md5” and “sha256”.

but both config parser and all tools accepts ALL digests defined in "digest-{openssl,glibc}.c" in array digests[], which contains much more of them and which do not have any support and can lead to misunderstanding. I propose to strip the list according to documentation. But it collides a bit with the other proposal:


 2) As I stated in previously mentioned bugzilla, it would be great to have the way to show more Fingerprint types, since the most of the servers still provide only the old fingerprint (and for some years probably will). Also it is not preferable to stuck with old md5 as default. You can admit, that users can always do

 $ ssh server -oFingerprintHash=md5

but it is probably too much for users if they really want to verify fingerpring provided through other channel.

My proposal is to add ability to provide a list of digest that will be printed (not only one) and as a transition default use both available: "sha256,md5".


I don't have a patch yet, but if there would be some idea how can we make the transition more smooth, feel free to comment.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1249626
Comment 1 Jakub Jelen 2015-08-07 18:27:32 AEST 
Created attachment 2681 [details]
Allow more fingerprint algorithms on client side

Adding patch for client side, which introduces new default "sha256 md5". For internal operations and logging, only the first one is used, but for interaction with user (adding new host), both fingerprints are printed.

From my point of view, there is no need to do the same on the server side, since there is no interaction with user.
Comment 2 Damien Miller 2016-02-26 14:44:25 AEDT 
Retarget to openssh-7.3
Comment 3 Damien Miller 2016-02-26 14:47:21 AEDT 
Retarget to openssh-7.3
Comment 4 Damien Miller 2016-07-22 14:10:54 AEST 
retarget unfinished bugs to next release
Comment 5 Damien Miller 2016-07-22 14:14:38 AEST 
retarget unfinished bugs to next release
Comment 6 Damien Miller 2016-07-22 14:15:47 AEST 
retarget unfinished bugs to next release
Comment 7 Damien Miller 2016-07-22 14:17:12 AEST 
retarget unfinished bugs to next release
Comment 8 Damien Miller 2016-12-16 14:31:21 AEDT 
OpenSSH 7.4 release is closing; punt the bugs to 7.5
Comment 9 Damien Miller 2017-06-30 13:43:19 AEST 
Move incomplete bugs to openssh-7.6 target since 7.5 shipped a while back.

To calibrate expectations, there's little chance all of these are going to make 7.6.
Comment 10 Damien Miller 2017-06-30 13:44:22 AEST 
remove 7.5 target
Comment 11 Damien Miller 2018-04-06 13:12:13 AEST 
Move to OpenSSH 7.8 tracking bug
Comment 12 Damien Miller 2018-08-10 11:37:58 AEST 
Retarget remaining bugs planned for 7.8 release to 7.9
Comment 13 Damien Miller 2018-08-10 11:38:25 AEST 
Retarget remaining bugs planned for 7.8 release to 7.9
Comment 14 Damien Miller 2018-10-19 17:13:42 AEDT 
Retarget unfinished bugs to OpenSSH 8.0
Comment 15 Damien Miller 2018-10-19 17:14:48 AEDT 
Retarget unfinished bugs to OpenSSH 8.0
Comment 16 Damien Miller 2018-10-19 17:15:50 AEDT 
Retarget unfinished bugs to OpenSSH 8.0
Comment 17 Damien Miller 2019-02-22 14:21:09 AEDT 
I don't think I want to move forward with this change - the sha256 signatures are a lot more ubiquitous and accepted than they were in 2016 and I want to hasten the day when OpenSSH and its dependencies can compile without any MD5 support at all.
Comment 18 Damien Miller 2021-04-23 14:58:49 AEST 
closing resolved bugs as of 8.6p1 release