New classical computing attack drastically reduces effort needed to break RSA encryption

A team of cryptographers has uncovered a novel attack against RSA that sidesteps the traditional path of breaking the encryption by factoring massive numbers. Instead, the new approach enables signature forgery using classical computers, potentially making RSA much faster to compromise than previously believed possible.

A surprising conceptual shift#

For decades, the cryptographic community assumed that breaking RSA required one unavoidable step: factoring the public key to recover the private key. This computational hurdle has kept RSA secure for years, with estimates suggesting that cracking a 1024-bit key would demand tens of millions of dollars in computing resources—a burden only nation-states or tech giants could bear. For 2048-bit and larger keys, the effort seemed entirely out of reach.

The newly discovered forgery attack overturns this assumption. By enabling attackers to forge valid RSA signatures without first factoring the key, the method dramatically lowers the computational barrier. "If this result holds up under peer review, it would indeed be a conceptual break-through," says Karsten Nohl, a cryptography researcher at Allurity. "RSA is as difficult to break as it is to factor large integers, at least so we thought."

Current practical impact remains limited#

The research poses little immediate danger to most modern systems. Attacks remain computationally expensive enough that only well-resourced adversaries could carry them out, and widely deployed RSA implementations appear to remain secure. The main concern centers on deprecated 1024-bit keys, where the method brings practical compromise closer to feasibility.

However, the technique also degrades security margins for 2048-bit and 4096-bit keys, pushing them toward unacceptable thresholds. Industry standards from the NSA, NIST, and the European Union require that cryptographic systems maintain at least 128 bits of security—a level that represents 2^128 computations. The new attack reduces this safety margin.

Why this matters for cryptography's future#

The breakthrough signals that RSA's vulnerabilities may extend beyond the long-feared arrival of practical quantum computers. It demonstrates that classical computing alone may open new avenues to compromise what was thought to be one of the most robust encryption systems ever created.