Header of zimbraPasswordHistory

[Spooky]

Hello everyone I'm Zimbra newby from Thailand

Now I'm developing new software that authenticate and manage password via OpenLDAP of Zimbra. So my problem is I want to use Unique password history too. Then I view the value of zimbraPasswordHistory then I can see 13 digits number added on the old password like this

1253680219241:{SSHA}cpRNLRJN0XMjfB9T9UKtdoy1eF6qJ9 iK

What is these numbers?
How does it generated?
and How Zimbra check these History? (check from header , from Encrypted old password or both of them)

Thanks in advance for your help