SimplyTapp, the US firm that claims to have invented host card emulation (HCE) technology, has raised $5.9 million in a Series B round, as it seeks to further develop its cloud-based technology for NFC mobile payments, access control and in-app payments.

The firm says it has now raised a total of $7.6 million, which sheds light on its undisclosed Series A round last year. The current total means the initial round pulled in $1.7 million.

However, SimplyTapp remains intent on maintaining some mystery — it will not reveal who ponied up in the second round, in addition to existing investors Blue Sky Capital and Lightspeed Venture Partners.

CEO Doug Yeager points to HCE’s inclusion in Android and its backing from MasterCard and Visa as causes for optimism, regarding SimplyTapp’s prospects.

The firm’s target market for its technology is banks, card issuers, transit authorities and retailers.