Before there was Signal, before there was WhatsApp, the realm of secure encrypted messaging was ruled by the Off-the-Record secure messaging protocol, created as an alternative to PGP that introduced security properties like forward secrecy and deniability that were considered exotic at the time. Now, more than a decade later, Off-the-Record messaging, or OTR, has been largely sidelined by Signal variants. But a small team of cryptography engineers is still working on pushing Off-the-Record messaging forward by focusing on use cases that they argue aren’t sufficiently covered by Signal. But what even is deniability, and how much does it matter in the real-world context of secure messaging? Sofía Celi joins us in today’s episode to talk about this and more. Links and papers discussed in the show: OTRv4 Music composed by Toby Fox and performed by Sean Schafianski. Special Guest: Sofía Celi.