TY - GEN
T1 - SAID
T2 - 4th IEEE European Symposium on Security and Privacy, EURO S and P 2019
AU - Blazy, Olivier
AU - Bossuat, Angele
AU - Bultel, Xavier
AU - Fouque, Pierre Alain
AU - Onete, Cristina
AU - Pagnin, Elena
N1 - Publisher Copyright:
© 2019 IEEE.
PY - 2019/6/1
Y1 - 2019/6/1
N2 - As messaging applications are becoming increasingly popular, it is of utmost importance to analyze their security and mitigate existing weaknesses. This paper focuses on one of the most acclaimed messaging applications: Signal. Signal is a protocol that provides end-to-end channel security, forward secrecy, and post-compromise security. These features are achieved thanks to a key-ratcheting mechanism that updates the key material at every message. Due to its high security impact, Signal's key-ratcheting has recently been formalized, along with an analysis of its security. In this paper, we revisit Signal, describing some attacks against the original design and proposing SAID: Signal Authenticated and IDentity-based. As the name indicates, our protocol relies on an identity-based setup, which allows us to dispense with Signal's centralized server. We use the identity-based long-term secrets to obtain persistent and explicit authentication, such that SAID achieves higher security guarantees than Signal. We prove the security of SAID not only in the Authenticated Key Exchange (AKE) model (as done by previous work), but also in the Authenticated and Confidential Channel Establishment (ACCE) model, which we adapted and redefined for SAID and asynchronous messaging protocols in general into a model we call identity-based Multistage Asynchronous Messaging (iMAM). We believe our model to be more faithful in particular to the true security of Signal, whose use of the message keys prevents them from achieving the composable guarantee claimed by previous analysis.
AB - As messaging applications are becoming increasingly popular, it is of utmost importance to analyze their security and mitigate existing weaknesses. This paper focuses on one of the most acclaimed messaging applications: Signal. Signal is a protocol that provides end-to-end channel security, forward secrecy, and post-compromise security. These features are achieved thanks to a key-ratcheting mechanism that updates the key material at every message. Due to its high security impact, Signal's key-ratcheting has recently been formalized, along with an analysis of its security. In this paper, we revisit Signal, describing some attacks against the original design and proposing SAID: Signal Authenticated and IDentity-based. As the name indicates, our protocol relies on an identity-based setup, which allows us to dispense with Signal's centralized server. We use the identity-based long-term secrets to obtain persistent and explicit authentication, such that SAID achieves higher security guarantees than Signal. We prove the security of SAID not only in the Authenticated Key Exchange (AKE) model (as done by previous work), but also in the Authenticated and Confidential Channel Establishment (ACCE) model, which we adapted and redefined for SAID and asynchronous messaging protocols in general into a model we call identity-based Multistage Asynchronous Messaging (iMAM). We believe our model to be more faithful in particular to the true security of Signal, whose use of the message keys prevents them from achieving the composable guarantee claimed by previous analysis.
KW - Key Exchange
KW - Key ratcheting
KW - Post compromise security
KW - Signal
U2 - 10.1109/EuroSP.2019.00030
DO - 10.1109/EuroSP.2019.00030
M3 - Conference contribution
AN - SCOPUS:85072019432
T3 - Proceedings - 4th IEEE European Symposium on Security and Privacy, EURO S and P 2019
SP - 294
EP - 309
BT - Proceedings - 4th IEEE European Symposium on Security and Privacy, EURO S and P 2019
PB - Institute of Electrical and Electronics Engineers Inc.
Y2 - 17 June 2019 through 19 June 2019
ER -