Use salted SHA-512 passwords through crypt(3) instead of SSHA. Makes
it possible to use the same salts in /etc/shadow.

http://www.openldap.org/lists/openldap-technical/201305/msg00002.html

password-hash {CRYPT}
password-crypt-salt-format "$6$%.12s"

The salt format here is '$6$' which invokes a SHA512-based hash method
and provides 12 characters (72 bits) of salt. It uses the default 5000
iterations. The table on Hashcat's home page suggests that this is around
50,000 times stronger than the simple SSHA1 hash.