In the US government's ongoing campaign to protect data in the age of quantum computers, a new and powerful attack that used a single traditional computer to completely break a fourth-round candidate highlights the risks involved in standardizing the next generation of encryption algorithms.

Last month, the US Department of Commerce's National Institute of Standards and Technology, or NIST, selected four post-quantum computing encryption algorithms to replace algorithms like RSA, Diffie-Hellman, and elliptic curve Diffie-Hellman, which are unable to withstand attacks from a quantum computer.

In the same move, NIST advanced four additional algorithms as potential replacements pending further testing in hopes one or more of them may also be suitable encryption alternatives in a post-quantum world. The new attack breaks SIKE, which is one of the latter four additional algorithms. The attack has no impact on the four PQC algorithms selected by NIST as approved standards, all of which rely on completely different mathematical techniques than SIKE.

Getting totally SIKEd

SIKE—short for Supersingular Isogeny Key Encapsulation—is now likely out of the running thanks to research that was published over the weekend by researchers from the Computer Security and Industrial Cryptography group at KU Leuven. The paper, titled An Efficient Key Recovery Attack on SIDH (Preliminary Version), described a technique that uses complex mathematics and a single traditional PC to recover the encryption keys protecting the SIKE-protected transactions. The entire process requires only about an hour’s time. The feat makes the researchers, Wouter Castryck and Thomas Decru eligible for a $50,000 reward from NIST.

“The newly uncovered weakness is clearly a major blow to SIKE,” David Jao, a professor at the University of Waterloo and co-inventor of SIKE, wrote in an email. “The attack is really unexpected.”