Google Online Security Blog: Post-Quantum Cryptography: Standards and Progress

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Post-Quantum Cryptography: Standards and Progress

13. August 2024

Posted by Royal Hansen, VP, Privacy, Safety and Security Engineering, Google, and Phil Venables, VP, TI Security & CISO, Google Cloud The National Institute of Standards and Technology (NIST) just released three finalized standards for post-quantum cryptography (PQC) covering public key encapsulation and two forms of digital signatures. In progress since 2016, this achievement represents a major milestone towards standards development that will keep information on the Internet secure and confidential for many years to come. Here's a brief overview of what PQC is, how Google is using PQC, and how other organizations can adopt these new standards. You can also read more about PQC and Google's role in the standardization process in this 2022 post from Cloud CISO Phil Venables. What is PQC? Encryption is central to keeping information confidential and secure on the Internet. Today, most Internet sessions in modern browsers are encrypted to prevent anyone from eavesdropping or altering the data in transit. Digital signatures are also crucial to online trust, from code signing proving that programs haven't been tampered with, to signals that can be relied on for confirming online identity. Modern encryption technologies are secure because the computing power required to "crack the code" is very large; larger than any computer in existence today or the foreseeable future. Unfortunately, that's an advantage that won't last forever. Practical large-scale quantum computers are still years away, but computer scientists have known for decades that a cryptographically relevant quantum computer (CRQC) could break existing forms of asymmetric key cryptography. PQC is the effort to defend against that risk, by defining standards and collaboratively implementing new algorithms that will resist attacks by both classical and quantum computers. You don't need a quantum computer to use post-quantum cryptography, or to prepare. All of the standards released by NIST today run on the classical computers we currently use. How is encryption at risk? While a CRQC doesn't exist yet, devices and data from today will still be relevant in future. Some risks are already here:

Stored Data Through an attack known as Store Now, Decrypt Later, encrypted data captured and saved by attackers is stored for later decryption, with the help of as-yet unbuilt quantum computers

Hardware Products Defenders must ensure that future attackers cannot forge a digital signature and implant compromised firmware, or software updates, on pre-quantum devices that are still in use

For more information on CRQC-related risks, see our PQC Threat Model post. How can organizations prepare for PQC migrations? Migrating to new cryptographic algorithms is often a slow process, even when weaknesses affect widely-used crypto systems, because of organizational and logistical challenges in fully completing the transition to new technologies. For example, NIST deprecated SHA-1 hashing algorithms in 2011 and recommends complete phase-out by 2030. That’s why it's crucial to take steps now to improve organizational preparedness, independent of PQC, with the goal of making your transition to PQC easier. These crypto agility best practices can be enacted anytime:

Cryptographic inventory Understanding where and how organizations are using cryptography includes knowing what cryptographic algorithms are in use, and critically, managing key material safely and securely

Key rotation Any new cryptographic system will require the ability to generate new keys and move them to production without causing outages. Just like testing recovery from backups, regularly testing key rotation should be part of any good resilience plan

Abstraction layers You can use a tool like Tink, Google's multi-language, cross-platform open source library, designed to make it easy for non-specialists to use cryptography safely, and to switch between cryptographic algorithms without extensive code refactoring

End-to-end testing PQC algorithms have different properties. Notably, public keys, ciphertexts, and signatures are significantly larger. Ensure that all layers of the stack function as expected

Our 2022 paper "Transitioning organizations to post-quantum cryptography" provides additional recommendations to help organizations prepare and this recent post from the Google Security Blog has more detail on cryptographic agility and key rotation. Google's PQC Commitments Google takes these risks seriously, and is taking steps on multiple fronts. Google began testing PQC in Chrome in 2016 and has been using PQC to protect internal communications since 2022. In May 2024, Chrome enabled ML-KEM by default for TLS 1.3 and QUIC on desktop. ML-KEM is also enabled on Google servers. Connections between Chrome Desktop and Google's products, such as Cloud Console or Gmail, are already experimentally protected with post-quantum key exchange. Google engineers have contributed to the standards released by NIST, as well as standards created by ISO, and have submitted Internet Drafts to the IETF for Trust Expressions, Merkle Tree Certificates, and managing state for hash-based signatures. Tink, Google's open source library that provides secure and easy-to-use cryptographic APIs, already provides experimental PQC algorithms in C++, and our engineers are working with partners to produce formally verified PQC implementations that can be used at Google, and beyond. As we make progress on our own PQC transition, Google will continue to provide PQC updates on Google services, with updates to come from Android, Chrome, Cloud, and others.