What Should Post-Quantum Cryptography Look Like?

As quantum computing starts barreling away from the theoretical world and into the  realm of reality, the security community is on a timer. Most experts say that once quantum computers come online, they'll have the computational powers to easily break modern cryptography. A new report out today from the Cloud Security Alliance's Quantum Safe Security Working Group says that security researchers, vendors and enterprises need to start working now if they want to beat quantum's cryptographic buzzer.

Considering how long it takes for the IT world to transition to new encryption measures when old ones wear thin, the CSA report warns that the window until quantum reaches widespread adoption - about 10 to 15 years - might not be as long as it seems right now. 

"Cryptographic transitions take time, often a very long time," the report explains, pointing to the decade-long transition it took to get from 1024- to 2048-bit RSA key sizes, or the move to elliptic curve-based cryptography (ECC). "The transition to quantum-resistant cryptography is likely to take at least ten years. It is therefore important to plan for transition as soon as possible," according to the report.

The good news is that researchers have been working on this problem for a long time and they've got some good ideas on where cryptography should be headed. For example, NIST just last month held a workshop that featured some 80 research submissions in its Post Quantum Crypography Standardization initiative. The CSA report offers a breakdown of five of the most promising categories of cryptographic methods that could stand as post-quantum cryptography alternatives.

The five major contending algorithmic classes are:

According to Roberta Faux, lead author of the CSA report, there are pros and cons for each class of algorithm and it's going to take some time for researchers, and later, security engineers, to figure out which is best for a workable standard. 

For example, she says the community is going to have to have a lively debate to balance out three big trade-offs, namely key size, bandwidth and confidence level. 

If you consider code-based schemes, they've got a fast computational speed and they've been around so long that they've got a high degree of confidence from many in the security community. But their key size is large - some might say impractically so, Faux says. Meanwhile, isogeny-based cryptography has got small key sizes but the computation is still expensive and it's relatively new so there's less confidence there.

"I think the community agrees that we still need more time  to investigate the wide range of post-quantum cryptographic algorithms," Faux says, "and [to] understand the issues involved in migrating from existing public key cryptography to post-quantum cryptography."

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