Paper 2024/357
Security analysis of the iMessage PQ3 protocol
Abstract
The iMessage PQ3 protocol is an end-to-end encrypted messaging protocol designed for exchanging data in long-lived sessions between two devices. It aims to provide classical and post-quantum confidentiality for forward secrecy and post-compromise secrecy, as well as classical authentication. Its initial authenticated key exchange is constructed from digital signatures plus elliptic curve Diffie–Hellman and post-quantum key exchanges; to derive per-message keys on an ongoing basis, it employs an adaptation of the Signal double ratchet that includes a post-quantum key encapsulation mechanism. This paper presents the cryptographic details of the PQ3 protocol and gives a reductionist security analysis by adapting the multi-stage key exchange security analysis of Signal by Cohn-Gordon et al. (J. Cryptology, 2020). The analysis shows that PQ3 provides confidentiality with forward secrecy and post-compromise security against both classical and quantum adversaries, in both the initial key exchange as well as the continuous rekeying phase of the protocol.
Metadata
- Available format(s)
-
PDF
- Category
- Cryptographic protocols
- Publication info
- Preprint.
- Keywords
- post-quantumsecure messagingiMessagePQ3
- Contact author(s)
- dstebila @ uwaterloo ca
- History
- 2024-03-01: approved
- 2024-02-28: received
- See all versions
- Short URL
- https://ia.cr/2024/357
- License
-
CC BY
BibTeX
@misc{cryptoeprint:2024/357, author = {Douglas Stebila}, title = {Security analysis of the {iMessage} {PQ3} protocol}, howpublished = {Cryptology {ePrint} Archive, Paper 2024/357}, year = {2024}, url = {https://eprint.iacr.org/2024/357} }