Key Transparency
키 투명성
A class of protocols in end-to-end encrypted communications that require the service provider to publish identity-to-public-key bindings in a cryptographically protected, append-only log, allowing any user to verify that their own key bindings remain consistent. First formalized as CONIKS by Melara et al. in 2015, key transparency has since been deployed by WhatsApp and Messenger, and is under standardization by the IETF Key Transparency working group. Without KT, a malicious or compromised server can distribute fake public keys to conduct a man-in-the-middle attack with no means for users to detect the substitution.
Sources
- Wikipedia (EN) Wikipedia: definition of key transparency as a mechanism allowing communicating parties to verify public keys used in end-to-end encryption via a publicly auditable log
- usenix.org Melara, Blankstein, Bonneau, Felten, Freedman (2015), CONIKS: Bringing Key Transparency to End Users, USENIX Security Symposium: the foundational academic paper that first formalized key transparency for end-user key verification
- engineering.fb.com Meta Engineering (2023): WhatsApp's deployment of key transparency via an Auditable Key Directory (AKD), detailing the append-only directory, third-party audit records, and how KT strengthens E2EE guarantees against server-side attacks
- ietf.org IETF Key Transparency Architecture (draft-ietf-keytrans-architecture-05, 2025): defines KT as a cryptographically protected append-only log for user public keys that makes malicious entries equally visible to affected users and their contacts, enabling detection of impersonation without trusting the service operator