Symantec, best known as the purveyor of the Norton antivirus software, is buying VeriSign's identity and authentication business for $1.28 billion cash.

That's the unit that sells the Secure Sockets Layer (SSL) certificates and Public Key Infrastructure (PKI) services that protect electronic payments and authenticate web sites. It did $410 million last year, representing roughly 40% of VeriSign's income.

The deal, which should close by September, also includes a majority stake in VeriSign Japan.

The sale leaves VeriSign with its Internet domain business; it has sold off or shut down some 20 other non-core operations the last few years to focus on registering and managing traffic to more than 100 million domain names that end with .com or .net.

Last month Symantec agreed to shell out $300 million for PGP, another company in the encryption game. It told Reuters that "devices are irrelevant" and that nowadays it's the content that has to be secured.

With the VeriSign assets, it's talking about "businesses incorporating identity security into a comprehensive framework so that IT can confidently and securely adopt new computing models, from cloud computing to social networking and mobile computing to user-owned devices."

A million web servers currently use VeriSign's SSL encryption and Symantec said the addressable market for the server and user authentication segment is estimated to reach $1.6 billion by 2013.

Symantec means to combine VeriSign's SSL certificates with its own Critical System Protection or Protection Suite for Servers. It also means to pair the cloud-based VeriSign Identity Protection (VIP) user authentication with the existing Identity Safe capabilities in Norton.

VeriSign has issued upwards of two million VIP credentials and has a network of hundreds of merchants.

Symantec expects the transaction to dilute its non-GAAP earning by nine cents in fiscal 2011 and to start to contribute in the September 2011 quarter.