Enhanced Certificate Transparency and End-to-End Encrypted Mail

Abstract

Abstract-The certificate authority model for authenticating public keys of websites has been attacked in recent years, and several proposals have been made to reinforce it. We develop and extend certificate transparency, a proposal in this direction, so that it efficiently handles certificate revocation. We show how this extension can be used to build a secure end-to-end email or messaging system using PKI with no requirement to trust certificate authorities, or to rely on complex peer-topeer key-signing arrangements such as PGP. This makes endto-end encrypted mail possible, with apparently few additional usability issues compared to unencrypted mail (specifically, users do not need to understand or concern themselves with keys or certificates). Underlying these ideas is a new attacker model appropriate for cloud computing, which we call "malicious-butcautious".

Obstacles to the Adoption of Secure Communication Tools

“…Popular E2E-encrypted tools (e.g., iMessage, WhatsApp, Signal) relieve users of key management; they simply query a trusted server that vouches for the authentic public keys of other users. Recent proposals attempt to limit the trust in these servers using transparency logs [37], [38], but this approach has not been deployed in practice.…”

Device Attacker Models: Fact and Fiction

“…Proof A is referred to as proof of presence and proof B is referred to as proof of extension. Certificate transparency has been extended to provide proofs of absence and proofs of currency [3]. Proof of absence demonstrates that any data having a given attribute is absent from the log.…”

“…Since the log will contain one current valid ephemeral certificate for each user, we need to use a log structure that supports efficient proof of currency when the log contains multiple valid certificates of different clients. One possible log structure is proposed in ECT [3].…”

“…Such a party is a witness who saw the usage of the compromised signing key. Certificate transparency (CT) [1], accountable key infrastructure (AKI) [2], enhanced certificate transparency (ECT) [3], and distributed transparent key infrastructure (DTKI) [4] are existing key infrastructures that can audit such key usage by recording signatures (i.e. certificates) into the log.…”

Balloon: A Forward-Secure Append-Only Persistent Authenticated Data Structure

“…-We define publicly verifiable consistency for an ADS scheme and show how it enables a forward-secure source (Section 6). Verifiable inserts can also have applications for monitors in, e.g., [3,10,11,12,21,26].…”