# Security when using same salt for different passwords, compared to using different salts?

I have this question I am struggling about:

For example, someone suggested improving UNIX authentication by defining 3 different passwords for a user that are stored in the shadow file. All three passwords are stored with the same salt value.

When a user wants to authenticate to some system, he must provide in the $i$ attempt to login, the $i$ mod 3 password. For example, in the first attempt he will provide the first password, in the second and fifth attempt he will provide the second password. Is such alteration to UNIX system increases security or not? And what happens when all passwords are stored with different salt value?

• "Security" against whom? – fkraiem Jun 9 '16 at 12:27
• Is i updated whenever a person actually logs in or for every login attempt? – Daan Bakker Jun 9 '16 at 12:48
• security against different attacks. i updated on each attempt. – Mark Rotman Jun 9 '16 at 13:56
• This sounds like a significant decrease in usability for only a negligible increase in security. If someone compromises one of my passwords, it just means they might have to try up to three logins before they get in. – Gordon Davisson Jun 9 '16 at 14:31