enable hmac-sha2-256, hmac-sha2-512 MAC algorithms
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
dropbear (Debian) |
Fix Released
|
Unknown
|
|||
dropbear (Ubuntu) |
Fix Released
|
Medium
|
Unassigned | ||
Trusty |
Fix Released
|
Medium
|
Brian Murray | ||
Utopic |
Fix Released
|
Medium
|
Brian Murray |
Bug Description
[Impact]
Since version 2013.56, dropbear has supported the hmac-sha2-256 and hmac-sha2-512 MAC algorithms. However, until version 2015.67 (released 2015-01-28), they have not been enabled by default. According to the dropbear changelog, enabling them is a matter of uncommenting the following two lines in options.h:
/*#define DROPBEAR_
/*#define DROPBEAR_
Due to recent NSA revelations, some people are recommending users disable certain algorithms. If the recommendations at <https:/
[Test Case]
Setup steps:
1. install dropbear and openssh-client:
sudo apt-get install dropbear openssh-client
2. if you have openssh-server installed, stop it:
sudo service ssh stop
3. make sure that the dropbear service is enabled by editing
/etc/
this:
NO_START=0
4. start the dropbear service:
sudo service dropbear start
Test steps:
5. try the hmac-sha2-256 MAC:
ssh -o UserKnownHostsF
-o MACs=hmac-sha2-256 localhost
6. try the hmac-sha2-512 MAC:
ssh -o UserKnownHostsF
-o MACs=hmac-sha2-512 localhost
Cleanup steps:
7. stop the dropbear service:
sudo service dropbear stop
8. if you edited /etc/default/
service, disable it again by editing /etc/default/
setting the NO_START variable to 1 like this:
NO_START=1
9. if you stopped the OpenSSH server, restart it:
sudo service ssh start
[Regression Potential]
* Upstream recently enabled these algorithms by default (version
2015.67 released 2015-01-28), so it is believed they are ready for
production use. The code implementing these hash algorithms has
not changed since 2013.56, so enabling these algorithms for
Trusty (based on 2013.60) should be as safe as enabling them for
Utopic (based on 2014.65). However, because the code has not been
enabled by default for long, it has probably not had as much field
testing and may be more likely to contain compatibility or
security bugs.
* SSH clients are likely to prefer the new MAC algorithms over the
old MAC algorithms. If either the client or server has an
implementation bug, the ability to connect may be impaired unless
the user configures the client to disallow the new algorithms or
prefer the old algorithms (e.g., via the ssh_config "MACs"
directive in OpenSSH).
* The new MAC algorithms may negatively impact performance.
Related branches
- Brian Murray: Approve
-
Diff: 33 lines (+21/-0)2 files modifieddebian/changelog (+6/-0)
debian/diff/0003-options.h-enable-hmac-sha2-256-and-512.diff (+15/-0)
- Brian Murray: Approve
-
Diff: 33 lines (+21/-0)2 files modifieddebian/changelog (+6/-0)
debian/diff/0004-options.h-enable-hmac-sha2-256-and-512.diff (+15/-0)
Changed in dropbear (Debian): | |
importance: | Undecided → Unknown |
status: | New → Unknown |
Changed in dropbear (Debian): | |
status: | Unknown → New |
Changed in dropbear (Ubuntu): | |
importance: | Undecided → Medium |
status: | New → Triaged |
tags: | added: trusty utopic vivid |
description: | updated |
Changed in dropbear (Ubuntu Trusty): | |
status: | New → Triaged |
Changed in dropbear (Ubuntu Utopic): | |
status: | New → Triaged |
Changed in dropbear (Ubuntu Trusty): | |
importance: | Undecided → Medium |
Changed in dropbear (Ubuntu Utopic): | |
importance: | Undecided → Medium |
tags: |
added: verification-done-trusty verification-done-utopic removed: verification-needed-trusty verification-needed-utopic |
Changed in dropbear (Debian): | |
status: | New → Fix Released |
Attached are debdiffs for trusty and utopic/vivid.