> They're enabled by default in 2015.67 Great! I updated the description.
** Description changed: [Impact] Since version 2013.56, dropbear has supported the hmac-sha2-256 and - hmac-sha2-512 MAC algorithms, but they are disabled by default. - According to the dropbear changelog, enabling them is a matter of - uncommenting the following two lines in options.h: + 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_SHA2_256_HMAC*/ - /*#define DROPBEAR_SHA2_512_HMAC*/ + /*#define DROPBEAR_SHA2_256_HMAC*/ + /*#define DROPBEAR_SHA2_512_HMAC*/ Due to recent NSA revelations, some people are recommending users disable certain algorithms. If the recommendations at <https://stribika.github.io/2015/01/04/secure-secure-shell.html> are followed, there are no MAC algorithms left that dropbear supports unless hmac-sha2-256 and hmac-sha2-512 are enabled. [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/default/dropbear and setting the NO_START variable to 0 like this: NO_START=0 4. start the dropbear service: sudo service dropbear start Test steps: 5. try the hmac-sha2-256 MAC: ssh -o UserKnownHostsFile=/dev/null \ -o MACs=hmac-sha2-256 localhost 6. try the hmac-sha2-512 MAC: ssh -o UserKnownHostsFile=/dev/null \ -o MACs=hmac-sha2-512 localhost Cleanup steps: 7. stop the dropbear service: sudo service dropbear stop 8. if you edited /etc/default/dropbear to enable the dropbear service, disable it again by editing /etc/default/dropbear and 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] - * Due to being disabled by default upstream, the implementations of - the new MAC algorithms are probably not as well tested as the old - MAC algorithms. This may increase the likelihood of compatibility - or security bugs. + * 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. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1409798 Title: enable hmac-sha2-256, hmac-sha2-512 MAC algorithms To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/dropbear/+bug/1409798/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
