In upgrading from ssh-1.1.25 to openssh-2.1.1p1, I've come across a pair of incompatibilities not mentioned in the UPGRADING list. The first involves the authorized_keys file: n. No un-quoted spaces are permitted in the options field of the authorized_keys file. While this was documented as a restriction in F-Secure SSH, in practice this was not enforced. OpenSSH does enforce this restriction. The second involves both the sshd_config and authorized_keys files. I encountered it with the authorized_keys file (as it made a key unusable), and I haven't tested how the OpenSSH sshd reacts to having the unavailable flags in sshd_config: m. Options unavailable in sshd_options and authorized_keys. The AccountExpireWarningDays, AllowForwardingPort, AllowForwardingTo, AllowHosts, AllowSHosts, AllowTcpForwarding, DenyForwardingPort, DenyForwardingTo, DenyHosts, DenySHosts, DenyTcpForwarding, ForcedEmptyPasswdChange, ForcedPasswdChange, IdleTimeout, IgnoreRootRhosts, PasswordExpireWarningDays, SilentDeny, TISAuthentication, and Umask options are not available in sshd_options. Similarly, the allowforwardingport, allowforwardingto, denyforwardingport, and denyforwardingto options are not available in authorized_keys. -- #include <disclaimer.h> /* Sten Drescher */ "This is the *NIX version of the 'ILOVEYOU' worm. It runs on the honor system. Forward this to everyone in your address book, and randomly delete some of your files." - Unknown