42741b1883
There's currently a bug in libssh that a handshake doesn't complete if there is no overlap between HMAC methods, but when an AEAD cipher is used. In case of an AEAD cipher such as chacha20-poly1305 or aes256-gcm, the HMAC algorithm that is being picked is not relevant. But the problem here is that the HMAC still needs to have an overlap in the handshake, even if it is not used afterwards. This was found with a very strict server side configuration with libssh where only AEAD ciphers and EtM HMAC modes are accepted. The client tested against was dropbear. Dropbear does have support for chacha20-poly1305 and AES GCM modes, but no support for EtM HMAC modes. This meant that the libssh server in this case rejected the dropbear client, even though it is perfectly able to serve it since dropbear supports AEAD algorithms. The fix implemented here updates the HMAC phase of the handshake to handle this case. If it detects an AEAD cipher is used, it uses the HMAC abbreviations for the method instead. This is the same name that is used in other places as well. It matches the client to server and server to client values, but it does depend on the order of things in the ssh_kex_types_e enum, which I'm assuming here is ok since it's explicit. I've looked at how to add a test for this, but I couldn't really find a suitable place for it. I would love some tips if this is easily possible, or if it's easier for someone else to contribute, that's of course welcome too. Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com> Reviewed-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com> Reviewed-by: Jakub Jelen <jjelen@redhat.com>
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The SSH library
Why?
Why not ? :) I've began to work on my own implementation of the ssh protocol because i didn't like the currently public ones. Not any allowed you to import and use the functions as a powerful library, and so i worked on a library-based SSH implementation which was non-existing in the free and open source software world.
How/Who?
If you downloaded this file, you must know what it is : a library for accessing ssh client services through C libraries calls in a simple manner. Everybody can use this software under the terms of the LGPL - see the COPYING file
If you ask yourself how to compile libssh, please read INSTALL before anything.
Where ?
Contributing
Please read the file 'CONTRIBUTING.md' next to this README file. It explains our copyright policy and how you should send patches for upstream inclusion.
Have fun and happy libssh hacking!
The libssh Team