When one has been in technology as long as I have, one tends to accrue battle scars and war stories as things change, things always change.
Things like SSH on macOS historically used the cryptosystem algorithm of Ron Rivest, Adi Shamir, and Len Adleman, or RSA as its default. As it’s fundamentally just applied math, even a quarter century ago, there were clearly known attacks, at least for some keys.
Today in 2025, macOS Sequoia’s ssh-keygen program generates Ed25519 keys by default, i.e. no longer RSA.
So that means if I want to access a computer or robotics system, like a Nao V5, from the period 2014-2018, and an associated rUNSWift code release, which doesn’t support Ed25519, I may well need to know how to go back to RSA.
As the fine folks at OSXDaily noted in 2022, assuming I kept a backup of at least my private SSH key from that era (which I thankfully have), it has been done at a Terminal prompt with the command:
sudo nano /etc/ssh/ssh_config
Plus adding the following lines and saving:
HostkeyAlgorithms +ssh-rsa
PubkeyAcceptedAlgorithms +ssh-rsa
From context, the default username was nao. This allowed me to plug in my Ethernet cable via a USB-C adapter, and so complete:
ssh nao@neytiri.local
The state I’d left Neytiri in was likely a fresh sync of the robot soccer team’s instructions from 2018, for example there was a Python error which I fixed for myself by renaming GameController.py to GameControllerV2.py and also changing the class name accordingly. It’s nice that some things coded from that era still work, like single chest button press and wait four to seven minutes for a successful power on, double chest press to stiffen, head stroke (or type after completing SSH) to start/kill the runswift program, and a lit up red right eye if a soccer ball is detected by runswift. It’s a shame both new(ish, not even a year?) Nao batteries are no longer holding their charge, so Neytiri struggles to stand up, let alone play some real soccer. But it’s also fair to say, nothing in this world lasts forever, indeed even heaven and earth will pass away. As good as it was collaborating with B-Human as B-Swift to win the Mixed Teams 2018, and of course be part of the outright rUNSWift Grand Final in 2015, perhaps it’s time to sunset this era of history, to close a chapter, as “The end of a matter is better than its beginning”, Ecclesiastes 7:8a (NIV).
I’m only two months into this Sabbatical period of my life. That stated, I’m also reminded that, to personalise 1 Corinthians 10:31, whether I eat or drink or whatever I do, I do it all for the glory of God.
I wonder what else God has planned to change in the next quarter century?
Peter Johannes Schmidt 