Artificial intelligence (AI) agents developed by Google DeepMind have shown new ways to make attacks against legacy RSA-1024 encryption systems significantly cheaper.
The research was conducted by Google DeepMind in collaboration with cryptography researchers from the University of California San Diego and Inria.
RSA is a widely used public-key cryptographic algorithm that relies on the mathematical difficulty of factoring large numbers. Although RSA-1024 was once considered sufficiently secure, advances in computing and cryptanalysis have made it unsuitable for protecting sensitive information. Modern systems generally use RSA keys of 2048 bits or longer.
The first major finding focused on digital signature forgery involving the PKCS#1 v1.5 padding format. Padding is additional data inserted into a message before signing to ensure that it meets the required block size. Researchers examined how this protection behaves when an attacker can influence the content of the message being signed.
The team found that when an attacker controls approximately half or more of the signed data block, the padding may no longer provide additional protection against forgery. This weakness is relevant to the PKCS#11 signing interface used by cryptographic devices, including hardware security modules.
To show the improvement, DeepMind's AI agents reproduced an earlier academic signature-forgery attack against an RSA-1024 key. The agents reduced the required computing time from approximately 1,380 CPU core-years to 391 CPU core-years, making the process around 3.5 times more efficient.
Two AI agents reportedly designed, executed and debugged the computation in less than four days, with approximately 20 messages from a human researcher, most of which involved approving their actions.
Researchers also developed a more efficient approach for situations where attackers control a smaller portion of the signed message, such as a 32-byte hash. Their theoretical calculations suggest that the proposed method could be approximately 1,600 times more efficient than the previous best approach for certain RSA-1024 signature-forgery scenarios.
The second major finding concerns RSA key factoring. RSA security depends on the difficulty of breaking down a large number into its original prime factors. The researchers developed an algorithm that could make factoring each additional RSA-1024 key approximately 30 times cheaper on average after an expensive initial computation.
However, this technique remains theoretical and has not yet been implemented. The initial computation would also require substantial resources, meaning the findings do not show an immediate practical attack against deployed encryption systems.
The researchers also highlighted important limitations of the signature-forgery technique. It requires approximately four billion signing queries in advance, does not recover the private key and does not work against devices that internally hash messages before signing.
According to Pushmeet Kohli, Vice President at Google DeepMind and Chief Scientist at Google Cloud, modern cryptographic protocols generally use RSA keys of 2048 bits or larger and remain secure against the demonstrated techniques.
