What is Apple PQ3 Encryption — Simple introduction

PQ3 is a level 3 security protocol which is used for encryption. This was designed to prevent attackers from gaining data using quantum computing. You may wonder why this was implemented now because we are still in the early stage of quantum computing. The reason is that the HNDL, which is called Harvest Now Decrypts Later. What does this mean? This is the method used by hackers to store the encrypted data now and decrypt it once the quantum computers come into play. The depth and importance of this protocol are to combat/ prevent such dangerous activities from being carried out

Signal adopted level 2 security called PQXDH. Apple used RSA and it later switched to Elliptic Curve Cryptography (ECC) until the IOS 17.3. Now with the IOS 17.4 Apple goes beyond the modern encryption methods and gives level 3 security which is PQC bandwagon with PQ3 which combines KYBER and ECC.

To understand the encryption we should first see what PQC is.

Understanding of PQC

With modern technology, the RSA 2048 encryption takes 300 trillion years to crack. But with a quantum computer, it takes only 10 seconds. Here you see how vulnerable our current encryption is once quantum computers become a reality. With PQC the process and encryption make it more complex. This eventually challenges the quantum computers to get it cracked. Having these encryption methods in place could prevent such attacks in the future

Types of post-quantum approaches

Lattice-based cryptography: It uses mathematical structures called lattices to encrypt data. The current RSA algorithm works using large prime numbers. Lattice algorithms rely on the difficulty of finding the right lattice point in a high-dimensional vector space.

Code-based cryptography: This is one of the easiest methods but it is of least security. This uses error-correcting code for encryption.

Multivariate cryptography: This is one of the quickest methods but also one of the least secure. This uses mathematical functions to encrypt data.

Hash-based cryptography: This uses the hash-based function to encrypt the data. This could be regarded as one of the most secure but it is also one of the slowest methods.

Isogeny-based cryptography: This method uses mathematical structures called isogenies for encrypting data. It is also known as one of the most secure but slowest methods. Modern algorithms such as ECC, rely on finding points on elliptic curves. Isogency-based algorithms extend this by mapping the original elliptic curve to an isogenous one, making it difficult to work backward without the right information.

Current status of PQC algorithm.

General encryption recommendation

CRYSTALS-Kyber: This is a lattice-based approach. This algorithm exchanges small encryption keys between two parties without foregoing too much speed.

Digital signature recommendation

CRYSTALS-DILITHIM: High efficiency and primary recommendation, a lattice-based approach.

FALCON: High efficient and lattice-based approach for applications that require smaller signatures.

Apple’s Approach

You may wonder now what is Apple’s approach and how this works. Apple limits the messages that can be decrypted using the same key. What it does is, it changes the key rotationally every 50 messages or every 7 days. So there is no one specific key to decrypt the whole conversation. The decryption key changes rotationally. This feature is unveiled with the IOS 17.4 update. It could be anticipated that other messaging platforms would choose to adopt this protocol in the future to come.