Im trying to use the arcfour cipher with SSH. Yes, I am aware of the risks, but I have my own reasons for wanting to use it. When I list available ciphers, it's not there. Is it possible to add it in?

Available ciphers:

$ ssh -Q cipher

Attempt to use arcfour:

$ ssh -c arcfour file2
Unknown cipher type 'arcfour'
  • Have you checked if the brew.sh version of openssh can enable or support that cipher? – bmike Mar 23 '19 at 16:39
  • @bmike It cannot. As noted in my answer, support for this cipher has been removed upstream. – duskwuff -inactive- Mar 23 '19 at 23:22
  • Well done @duskwuff trying to pull code that old to compile or a system / os that shipped three years ago seems the only workaround. – bmike Mar 24 '19 at 0:04

Support for Arcfour was disabled by default in OpenSSH 7.2 (Feb 2016), and was subsequently removed completely in OpenSSH 7.6 (Oct 2017). macOS 10.14 ships with OpenSSH 7.9, which is several major versions beyond this removal.

In theory, you could reverse some of the changes applied in OpenSSH 7.6 to readd support for Arcfour. However, doing so will require significant C programming experience.

In practice, I would advise you to reconsider what you are doing.

  • 2
    Thanks for this thorough answer. To resolve this, I created a virtual machine with an old OS that supported arcfour, did what I had to do, and then destroyed it. – Dave Mar 24 '19 at 18:04

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