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AtosNicoS opened this issue Aug 27, 2018 · 4 comments
Closed

Failed to negotiate key exchange algorithm #461

AtosNicoS opened this issue Aug 27, 2018 · 4 comments

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@AtosNicoS
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AtosNicoS commented Aug 27, 2018

Hi, I am using 2016.1.0 (from nuget) and I am trying to connect to a TeltonikaRUT955 Modem via SSH. I just updated the firmware to a newer version which has "Improved SSH security" in its changelog. I can no longer login via SSH.NET, only via Putty.

It seems that SSH.NET does not support newer cipher algorithms. Do you know more about this?
Putty logs the following:

2018-08-27 12:59:28	We claim version: SSH-2.0-PuTTY_Release_0.70
[...]
2018-08-27 12:59:28	Doing ECDH key exchange with curve Curve25519 and hash SHA-256
[...]
2018-08-27 12:59:30	Initialised AES-256 SDCTR client->server encryption
2018-08-27 12:59:30	Initialised HMAC-SHA-256 client->server MAC algorithm
2018-08-27 12:59:30	Initialised AES-256 SDCTR server->client encryption
2018-08-27 12:59:30	Initialised HMAC-SHA-256 server->client MAC algorithm
[...]

The router uses Dropbear v2018.76 as ssh client.

Downgrading the firmware is not an option in case of the SSH and overall system security.

@darkoperator
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darkoperator commented Aug 27, 2018 via email

@kv9y
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kv9y commented Jul 11, 2019

Is there any update on this? We needed to upgrade some hardware and it only supports the following algorithms: aes128-ctr; aes192-ctr; and aes256-ctr. If I can't get SSH.NET to work, I will likely need to move to a different SSH lib. I just don't have the time to fork this project and implement these ciphers.

@A20oz
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A20oz commented Aug 5, 2019

#461 (comment)

@drieseng
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drieseng commented Mar 6, 2020

In the develop branch, we now support curve25519-sha256 and
curve25519-sha256@libssh.org.

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5 participants