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Filezilla and other SFTP clients unable to connect due to server only supporting diffie-hellman-group1-sha1 key exchange algorithm
Posted by John Villanueva on 09 June 2016 09:09 PM

The latest version of FileZilla will have problems connecting to the SFTP service running on older versions of JSCAPE MFT Server. This is usually caused by the only key exchange algorithm supported by older versions of JSCAPE MFT Server - diffie-hellman-group1-sha1. Later versions of FileZilla (and perhaps other SFTP clients) no longer support it. 

In FileZilla, you'll get the following message:

Error: The first key-exchange algorithm supported by the server is diffie-hellman-group1-sha1, which is no longer secure. Aborting connection.
Error: Could not connect to server

To remedy this problem, you can either use older versions of SFTP clients or (HIGHLY RECOMMENDED) upgrade to the latest version of JSCAPE MFT Server, which already supports the following key exchange algorithms:

 

diffie-hellman-group1-sha1

diffie-hellman-group14-sha1

diffie-hellman-group-exchange-sha1

diffie-hellman-group-exchange-sha256

 

Note that old versions of MFT Server (prior to 9.1) have broken diffie-hellman-group-exchange-sha256 and diffie-hellman-group-exchange-sha1 key exchange algorithms

 

You may download the latest version of JSCAPE MFT Server from here:

http://www.jscape.com/downloads/jscape-mft-server

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