Cryptographers have identified a new approach to compromising RSA encryption that operates through signature forgery rather than the traditionally understood factoring method. The discovery challenges long-held assumptions about RSA’s security model and introduces a classical computing attack that requires substantially fewer computational resources than previously estimated. According to the research, the attack proves fully practical against 1024-bit RSA keys, requiring approximately 1,380 core-years of computation time compared to factoring estimates of 500,000 to 1 million core-years. For 2048-bit and 4096-bit implementations, the method reduces security levels to 290 and 2119 respectively, below the 128-bit minimum threshold required by the National Security Agency, National Institute of Standards and Technology, and European Union Agency for Network and Information Security. Researchers note that these security reductions could decrease further, as the initial work was completed without AI or GPU optimization. The vulnerability specifically affects blind-signature implementations of RSA, commonly known as textbook RSA. Most widely deployed RSA systems use PKCS or PSS padding formats that appear resistant to this particular attack vector. However, certain real-world systems do employ blind-signature RSA, notably Privacy Pass, a privacy-focused authentication protocol utilized by major technology companies including Apple and Cloudflare. The attack leverages a variant of the number field sieve algorithm from 2007, combined with an oracle property present in certain cryptographic protocols. By performing a massive volume of operations, attackers can accumulate sufficient information to forge signatures. An attack on Privacy Pass would theoretically require approximately 243 token requests, a volume comparable to Cloudflare’s daily network traffic according to the company’s public statements. Researchers and cryptographers emphasize that immediate practical threats remain limited, particularly for systems employing standard padding implementations. Nevertheless, the discovery reinforces the urgency of transitioning away from RSA-based systems toward quantum-resistant alternatives already in development.
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