$ ssh-keygen -t rsa1 -b 2048 -f t Generating public/private rsa1 key pair. t already exists. Overwrite (y/n)? y Enter passphrase (empty for no passphrase): Enter same passphrase again: Saving key "t" failed: unknown or unsupported key type $ I guess this is a consequence of dropping SSH v1 protocol support. (I was doing this because I have a program which uses RSA, relies on an external key generator, and understands the ssh v1 key format.) If ssh-keygen is not able to save in ssh1 RSA format, it should fail early rather than going to all of the effort of generating a key (this took a minute or two on my rpi) and then bombing out. I filed this bug originally against Debian's version, here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=888205
Thanks for the report. This has already been fixed in this commit which was included in the 7.6 release: https://github.com/openssh/openssh-portable/commit/873d3e7d $ ssh -V OpenSSH_7.6p1, OpenSSL 1.0.2m-fips 2 Nov 2017 $ ssh-keygen -t rsa1 -b 2048 -f t unknown key type rsa1
Close all resolved bugs after release of OpenSSH 7.7.