Support OpenSSH 8.8

OpenSSH 8.8 has disabled RSA signatures made with SHA1 by default. This seems to make SSH.net incompatible with it. When trying to connect with an application using SSH.Net, I get the following error:

Permission denied (publickey).

On the destination machine, the following is logged for the sshd daemon:

userauth_pubkey: key type ssh-rsa not in PubkeyAcceptedAlgorithms

In theory, regenerating keys with OpenSSH 8.8 should fix this problem, but in doing so, SSH.Net will no longer be able to read the new key, generating another error:

openssh key type: ssh-rsa is not supported

Sadly, I just have the stacktrace of the application I use for this, but maybe it helps:

Duplicati.Library.Interface.UserInformationException: Failed to parse the keyfile, check the key format and passphrase. Error message was openssh key type: ssh-rsa is not supported ---> Renci.SshNet.Common.SshException: openssh key type: ssh-rsa is not supported
Sep 29 20:31:18 htpc mono[1395173]:   at Renci.SshNet.PrivateKeyFile.ParseOpenSshV1Key (System.Byte[] keyFileData, System.String passPhrase) [0x000c3] in <8c66a76a693c4e52b456ec0712c863dd>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Renci.SshNet.PrivateKeyFile.Open (System.IO.Stream privateKey, System.String passPhrase) [0x00355] in <8c66a76a693c4e52b456ec0712c863dd>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Renci.SshNet.PrivateKeyFile..ctor (System.String fileName, System.String passPhrase) [0x00023] in <8c66a76a693c4e52b456ec0712c863dd>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Renci.SshNet.PrivateKeyFile..ctor (System.String fileName) [0x00000] in <8c66a76a693c4e52b456ec0712c863dd>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Library.Backend.SSHv2.ValidateKeyFile (System.String filename, System.String password) [0x0001f] in <64bc5fc0959e40abaaf59040a05bc63e>:0
Sep 29 20:31:18 htpc mono[1395173]:    --- End of inner exception stack trace ---
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Library.Backend.SSHv2.ValidateKeyFile (System.String filename, System.String password) [0x000ac] in <64bc5fc0959e40abaaf59040a05bc63e>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Library.Backend.SSHv2.CreateConnection () [0x0006e] in <64bc5fc0959e40abaaf59040a05bc63e>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Library.Backend.SSHv2+<List>d__42.MoveNext () [0x0002c] in <64bc5fc0959e40abaaf59040a05bc63e>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Library.Interface.BackendExtensions.TestList (Duplicati.Library.Interface.IBackend backend) [0x00017] in <0b09fcfcca1b440fab7c860158765270>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Library.Backend.SSHv2.Test () [0x00000] in <64bc5fc0959e40abaaf59040a05bc63e>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Server.WebServer.RESTMethods.RemoteOperation.TestConnection (System.String url, Duplicati.Server.WebServer.RESTMethods.RequestInfo info) [0x000b7] in <3752ce5d8337471da6b77129cfa4bdbe>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Server.WebServer.RESTMethods.RemoteOperation.POST (System.String key, Duplicati.Server.WebServer.RESTMethods.RequestInfo info) [0x00094] in <3752ce5d8337471da6b77129cfa4bdbe>:0
Sep 29 20:31:18 htpc mono[1395173]:   at Duplicati.Server.WebServer.RESTHandler.DoProcess (Duplicati.Server.WebServer.RESTMethods.RequestInfo info, System.String method, System.String module, System.String key) [0x00289] in <3752ce5d8337471da6b77129cfa4bdbe>:0

See https://www.openssh.com/txt/release-8.8 as well

[chrisdanna]

Any chance of publishing the package with this update soon? Even if a prerelease?

[darinkes]

Its already everything merged, just needs a new NuGet Release. See https://github.com/sshnet/SSH.NET/pull/614