A pure-Haskell SSH server library
#7Pull request for enum/ssh
Good evening,
in my fork at https://hub.darcs.net/enum/ssh I did the following changes:
- merged pointfree/ssh-curve25519-sha256 (in a way conforming to fr33domlovers refactorings)¹
- replaced SimpleAES by cryptonite, since cryptonite supports CTR and SimpleAES doesn't
- added CTR mode support, since OpenSSH has marked CBC mode as deprecated²; this would fix #6
¹) still has the drawback that tests are failing ²) more background information in "Plaintext Recovery Attacks Against SSH" http://www.isg.rhul.ac.uk/~kp/SandPfinal.pdf
- description updated
Manual test I used to make sure it actually works:
- clone https://hub.darcs.net/enum/ssh-server-conduit
- install into the same sandbox
- cabal run example
- remove localhost-related lines from ~/.ssh/config, such that OpenSSH really uses aes256-ctr
- "ssh -p 5033 clutzy@localhost -- count" (password: draconequus)
- it will tell you that the Environment command is unsupported
- type some text and hit ^D; the number of characters will be returned
It shows that the en- and decryption is working.
Sorry for being vey slow to respond! I'm afraid I've rather lost track of all the problems and different forks.
What should we do about the failing tests?
The first three patches seem simple to merge if they're useful to someone.
I don't see anything we can do about the failing tests - libssh2 still only supports Diffie-Hellman key exchange (which is deprecated in OpenSSH for a good reason) and there is no alternative client library for Haskell at the moment. Hence I propose to ignore or remove the failing tests and return to manual testing -- I agree this is not a good habit, but otherwise we'll be sticking with deprecated and broken algorithms forever.
As for “simple to merge”: they all mergeable without conflicts; what I did is the following (in this order):
- I cloned this fork
- I added support for custom data/EOF/interrupt handlers, since that was required to implement ssh-server-conduit properly (these changes are trivial; skip them if you like, it won't make a difference for the other patches)
- merged pointfree's fork ssh-curve25519-sha256 and sorted out all the conflicts already
- did the changes regarding cryptonite and CTR
Since there were no later commits in this repository, my fork is just a few patches ahead, without conflicts, and can be merged automatically.
For me, shifting to manual testing as a significant issue for future maintenance, though of course there's the obvious counter point that an untested usable package is better than an tested unusable package.
We discussed this a bit on #darcs: http://irclog.perlgeek.de/darcs/2018-04-24#i_16086929
I see two fairly easy options for keeping at least some testing coverage: re-enable the old kex so we can test the rest of the code even if not the kex, and switch to running the ssh command instead of an ssh library.
