New RSA Signature Forgery Attack Revealed
The research-stage vulnerability targets unpadded RSA implementations, creating new risks for legacy 1024-bit encryption.
Updated on Oct. 15, 2026 in Cybersecurity
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Researchers have demonstrated a new oracle-based attack capable of forging signatures on unpadded RSA implementations. This research-stage vulnerability primarily threatens deprecated 1024-bit RSA keys, though it also impacts the security levels of 2048-bit and 4096-bit variants.
Why it matters
The discovery exposes critical weaknesses in specific cryptographic protocols like Privacy Pass that rely on unpadded RSA, highlighting the ongoing risk of using outdated security standards. This finding likely accelerates the industry migration toward quantum-resistant cryptographic systems.
The attack utilizes a variant of the number field sieve algorithm to break unpadded RSA. It reduces 2048-bit keys to 2^90 operations and 4096-bit keys to 2^119 operations, falling below standard security expectations.
The details
The method uses an oracle-based approach, where attackers submit specific inputs to a system to gather the necessary data to reverse-engineer private information. By querying multiple inputs, researchers identified a mechanism to forge signatures on unpadded or textbook RSA. Crucially, the attack does not affect PKCS or PSS variants, which utilize specific padding schemes to prevent such mathematical exploitation.
Timeline
October 2026: Researchers reported the discovery of the RSA signature forgery method.
The Tech Race
This vulnerability underscores the fragility of legacy RSA standards as the industry shifts toward quantum-resistant cryptographic systems. It serves as a stark reminder that as computational power scales, reliance on aging protocols creates predictable windows for exploitation.
Systems using Privacy Pass must account for this risk, as an attack requires gathering approximately 2^43 tokens. Organizations still using 1024-bit RSA keys should expedite their decommissioning, as these are now vulnerable to signature forgery.
The takeaway
The effectiveness of this attack confirms that unpadded RSA is unsuitable for secure signature operations. Security teams should monitor future optimizations of this number field sieve variant to see if the security margin for 2048-bit keys diminishes further.
Further reading
For broader trends in encryption and threat mitigation, see Cybersecurity.
Source note: This article includes information reported by RocketNews.
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