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iOS 17.4 iMessage PQ3 quantum security update explained – what does it mean?

iMessage's highest ever security protocol, explained.
Last Updated on February 23, 2024
iOS 17.4 iMessage PQ3 quantum security update explained - what does it mean? Image shows the iMessage logo on a purple gradient background.
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So, iOS 17.4 is bringing a PQ3 quantum security update to iMessage – but what does that actually mean for the average iPhone user? In the fast-evolving world of technology, ensuring the security of our digital communications has become paramount. Apple, being at the forefront of innovation, has recently announced a groundbreaking update to its iMessage platform.

With the release of iOS 17.4, Apple has introduced the PQ3 protocol. This state-of-the-art post-quantum cryptographic protocol aims to provide the highest level of security for iMessage. In this article, we’ll explain a few of the essential details of this new protocol, its significance, and how it sets a new standard for messaging security.

What is the iMessage PQ3 protocol?

The PQ3 protocol is a cutting-edge post-quantum cryptographic protocol developed by Apple for iMessage. It’s designed to provide extensive defences against highly sophisticated quantum attacks; Apple already has encryption in iMessage, but this is taking things above and beyond the next level.

Unlike previous messaging protocols, PQ3 qualifies as a “Level 3 security” protocol, making it the first of its kind to achieve this level of security. Essentially, PQ3 uses post-quantum cryptography (algorithms secure against a cryptanalytic attack by a quantum computer) to secure both the initial key establishment as well as any ongoing message exchange. To put it simply, it’s very advanced, and should keep iMessage future-proofed against the security threat of quantum computers.

A diagram illustrating the various stages of security in iOS, particularly focusing on iMessage.
Screenshot: Apple (https://security.apple.com/blog/imessage-pq3/)

Why is Apple using the PQ3 protocol in iOS 17.4?

Apple’s decision to shift to the PQ3 protocol for iMessage stems from the need to enhance the existing security measures against potential future quantum attacks. While iMessage has always supported end-to-end encryption, the existing cryptographic algorithms used by messaging apps rely on mathematical problems that could actually be solved by future quantum computers. PQ3, however, offers protection against “Harvest Now, Decrypt Later” attacks, providing users with an added layer of security.

Will the PQ3 protocol have any impact on iMessage performance?

While the PQ3 protocol introduces additional encryption and security measures, Apple has worked extensively to ensure that it does not negatively impact the performance of iMessage. Users can expect the same seamless messaging experience while enjoying the enhanced security features provided by PQ3.

Is the PQ3 protocol backwards compatible with older versions of iMessage?

No, the PQ3 protocol is not backwards compatible with older versions of iMessage. To benefit from the enhanced security features of PQ3, users must update their devices to the latest software versions. Luckily, we’ve dived into a step-by-step giving you the details of how to get your iPhone ready for the iOS 17.4 update if you’re looking forward to its full release at the beginning of March.


The introduction of the iOS 17.4 iMessage PQ3 protocol marks a significant milestone in messaging security. Apple’s commitment to protecting user privacy and data integrity is evident in the development of this state-of-the-art post-quantum cryptographic protocol. With its extensive defences against quantum attacks, PQ3 sets a new standard for messaging encryption: Apple continues to innovate and prioritize user security, and iMessage users can look forward to a more secure and private messaging experience.

Marla writes across a wide range of topics across PC Guide, including AI, PC hardware, and news on the latest tech releases. She's a passionate writer that's interested in the future of technology.