Comment by pdw

To the best of my knowledge, only OpenBSD and Fedora have a crypt(3) that returns NULL. Everybody else returns a string starting with "*" on error.

For example on Debian the manpage says:

> Upon error, crypt_r, crypt_rn, and crypt_ra write an _invalid_ hash to the output field of their _data_ argument, and crypt writes an invalid hash to its static storage area. This string will be shorter than 13 characters, will begin with a ‘*’, and will not compare equal to _setting_.