PTB Ventures and Accel have co-led a series A round for Callsign, an authentication platform backed by digital consultancy Reply.

Callsign, a UK-based authentication platform backed by digital consultancy Reply, has raised $35m in a series A round co-led by venture capital firms Accel and PTB Ventures.

The round also featured VC firm Allegis Capital and NightDragon Security, the investment fund formed by cybersecurity industry veteran David DeWalt.

Founded in 2012, Callsign has developed an artificial intelligence-based platform called Intelligence Driven Authentication (IDA) that enables companies to authenticate callers in real time using an individualised risk profile, while generating the…