Rebex.Net.SftpException: The client and the server have no common algorithms.

Question

Currently, we are using
Rebex.sftp.dll Version - 3.0.47

with this version, we are enabled to connect.
getting the below error

Rebex.Net.SftpException: The client and the server have no common algorithms.

After Updating Rebex.sftp.dll to the latest Version 5.0.799 working fine.

if the latest version is the fixing we need to upgrade
or we are missing anything in the existing version

Full Error Information

Rebex.Net.SftpException: The client and the server have no common algorithms. ---> Rebex.Net.SshException: The client and the server have no common algorithms.
at Rebex.Net.SshSession.qzm1d(Byte[] )
at Rebex.Net.SshSession.14Ad4fZ()
at Rebex.Net.SshSession.Negotiate()
at Rebex.Net.Sftp.1J4sBU.qzm1d(ZD5WJ )
at Rebex.Net.Sftp.2eOMSNZ(String , Int32 , SshParameters , ZD5WJ )
--- End of inner exception stack trace ---
at Rebex.Net.Sftp.2eOMSNZ(String , Int32 , SshParameters , ZD5WJ )
at Rebex.Net.Sftp.iINPXZ(String , Int32 , SshParameters )
at Rebex.Net.Sftp.Connect(String serverName, Int32 serverPort)

Please Help me with this.

Thanks in advance

Answer 1

Rebex SFTP v3.0.4700 is more than 9 years old, which means its SSH cipher support is now outdated. This makes these old Rebex SFTP releases no longer suitable for use with up-to-date SFTP/SSH servers.

For example, OpenSSH recently deprecated ssh-rsa host key cipher, because it is based on SHA-1, which is no longer considered secure. Replacement ciphers are rsa-sha2-256 and rsa-sha2-512 (specified by RFC 8332), but these are only supported in Rebex SFTP v3.0.6291 or higher. They did not exist in 2012 when v3.0.4700 was released.

Additionally, the old version of Rebex SFTP lacks support for MAC ciphers based on SHA-2 (such as hmac-sha2-256 or hmac-sha2-256) and only support MAC ciphers based on SHA-1 and MD5, both of which are no longer considered secure, and contemporary SFTP/SSH servers no longer support them (or enable them by default). Rebex SFTP v3.0.5171 added support for these in 2014.

One or both of these are almost certainly the cause of "The client and the server have no common algorithms" error you see, and upgrading to a more recent Rebex SFTP release would fix the problem.

If you would like to discuss your upgrading options, please contact us at sales@rebex.net.