Recently unable to connect via SFTP to reMarkable tablet

Help & Support
1

Hello, I'm using the most recent (non-Beta) release of Dopus 12. I'm no longer able to connect to my reMarkable 1 tablet via FTP feature of Dopus. I've never had trouble with this before (for almost two years), and I haven't changed my connection settings. It only started when I received a replacement tablet for my defective one. So I'm suspicious that the problem is with the reMarkable tablet. However, they're saying otherwise. Here is the FTP log from Dopus 12:

Opening Connection 10.11.99.1:22
Server version: SSH-2.0-dropbear_2019.78
Using SSH protocol version 2
We claim version: SSH-2.0-PuTTY_Directory_Opus
Couldn't agree a key exchange algorithm (available: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group14-sha256,kexguess2@matt.ucc.asn.au)
SSH: Fatal: Couldn't agree a key exchange algorithm (available: curve25519-sha256,curve25519-sha256@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group14-sha256,kexguess2@matt.ucc.asn.au)
Connection closed

Troubleshooting I've done:
*Restart Computer
*Restart reMarkable
*Reflash reMarkable with reMarkable-provided tool
*FileZilla - I can connect via SSH
*SSH using PowerShell in Windows 10 (successful)
*Most recent version of Putty (SSH connection successful)

Am I missing something here? Someone on reddit replied to my question that my client not supporting the ciphers in the FTP log is a "red flag." Perhaps Dopus does support them and the log is misleading and the problem is elsewhere / lies with the reMarkable?

Thanks for any help...I'm out of ideas.

2

The new tablet must be running a different version, or different configuration, of the SFTP server which doesn't like any of the encryption methods Opus supports.

Is the server something you can configure, or is it more of a black box solution?

3

Hi, Leo. Unfortunately, nothing I can configure (at least with my level of knowledge). It' a linux-based tablet, and I can SSH into it, but my knowledge of linux is zero.

4

There's no way to change which encryption algorithms the Opus side supports, so configuring the server would be the only option, at least until when/if we add more algorithms into Opus. If it worked in the past then it must be possible, but I know even less about the server than you do. If it's a full linux tablet that you have root access to then you should be able to configure it to do whatever you want.

5

Thanks, Leo. I guess for now I'll have to connect with a client other than Opus. Several people on Reddit and a facebook group for reMarkable tablet have suggested that reMarkable removed some older and less secure algorithms. Will there be similar deactivation and replacement with newer and more secure algorithms with Directory Opus down the road? Someone even used the term "red flag" re: Opus still including some outdated and thus insecure algorithms, but I'm out of my league in terms of knowing whether that's true or not.

6

We have added support for the elliptic curve algorithms in 12.26.3 beta.

1 Like
7

Great! Thanks, for letting me know Jon, and I'll give it a whirl when available in the next full release!