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Can't connect (SCP, SSH) in Xamarin Android

See original GitHub issue

Calling Connect() with an SSH or SCP client (and likely others) causes this exception. Does this library not work in Xamarin Android?

I don’t see where in this library ti’s throwing NotImplementedException, so I’m guessing something missing in Mono / .NET Standard?

2021-04-15 12:29:05.030 16384-16427/? E/MySessionStarter: Failed uploading file: System.NotImplementedException: The method or operation is not implemented.
      at Renci.SshNet.Session.WaitOnHandle (System.Threading.WaitHandle waitHandle, System.TimeSpan timeout) [0x00041] in <c7169cd606324a41b931acc40c516428>:0 
      at Renci.SshNet.Session.WaitOnHandle (System.Threading.WaitHandle waitHandle) [0x0000d] in <c7169cd606324a41b931acc40c516428>:0 
      at Renci.SshNet.Session.Connect () [0x0017b] in <c7169cd606324a41b931acc40c516428>:0 
      at Renci.SshNet.BaseClient.CreateAndConnectSession () [0x00053] in <c7169cd606324a41b931acc40c516428>:0 
      at Renci.SshNet.BaseClient.Connect () [0x0001f] in <c7169cd606324a41b931acc40c516428>:0 
    ....
    ```

Issue Analytics

State:
Created 2 years ago
Reactions:1
Comments:13

Top GitHub Comments

1reaction

ts678commented, May 22, 2021

A workaround is try new ECDsaCng() to see if it’s implemented. If exception occurs, go through HostKeyAlgorithms.Keys, and HostKeyAlgorithms.Remove(key) the ones beginning with ecdsa (inspired by Limit what algorithms or ciphers are used #730).

1reaction

ts678commented, May 12, 2021

It’s related to Session.WaitOnHandle being not implemented.

It seems Session.WaitOnHandle is in https://github.com/sshnet/SSH.NET/blob/develop/src/Renci.SshNet/Session.cs You can see comments there about the receive thread. I’m not an SSH.NET developer. It’d be nice if they can help.

It might be waiting at the below for the receive thread to either receive, or find an exception, and it got exception:

https://github.com/sshnet/SSH.NET/blob/f072c5f1a1bb607797a85cd43cf498ec541af3ab/src/Renci.SshNet/Session.cs#L852-L852

I think my issue is happening way before a connection

The stack trace names suggest that it’s working on connect, but it likely died before SSH connection was finished. The behavior we see with certain SFTP servers such as Bitvise (but not OpenSSH, at least so far) is a failure after a

Server: Elliptic Curve Diffie-Hellman Key Exchange Reply, New Keys Message Code: Elliptic Curve Diffie-Hellman Key Exchange Reply (31) is received, containing KEX host key (type: ecdsa-sha2-nistp384) I think the received protocol is RFC 5656 ECDH Key Exchange here.

Processing of that server SSH_MSG_KEX_ECDH_REPLY might be here:

https://github.com/sshnet/SSH.NET/blob/f072c5f1a1bb607797a85cd43cf498ec541af3ab/src/Renci.SshNet/Session.cs#L1298-L1302

and at some point the key from the server might hit here:

https://github.com/sshnet/SSH.NET/blob/a5bd08d655bb6a3c762306472cec354556dca3a3/src/Renci.SshNet/Security/Cryptography/EcdsaKey.cs#L238-L242

ECDsa Class and ECDsaCng Class get involved, and so maybe it hits the NotImplementedException around here.

NotImplementedException has been in ECDsaCng.cs a long time, maybe added here, then later exposed through Support newer SSH Ciphers and MACs #53. If you’re still on the 2016 release, ignore all this. It applies to 2020’s.

Any SSH.NET developer comments? Could these very welcome new capabilities be exposing an old gap in mono? Please forgive any mistakes in the details. I don’t have a debugger, or know the protocol or the code all that well.