The researchers recommend the implementation of signature validation mechanisms, like those in OpenSSH utilizing OpenSSL for signature generation, to counteract potential key retrieval by attackers exploiting faults in CRT-RSA signature computation. Zyxel addressed the risk by transitioning to OpenSSL in their ZLD firmware. Cisco introduced mitigations in ASA and FTD Software and is exploring further measures in IOS and IOS XE Software. Following notification, Cisco and Zyxel investigated the issue. The bulk of compromised keys originated from vulnerable implementations, notably from Zyxel devices. While their testing did not cover RSA-1024, SHA512 due to complexity, their lattice attack successfully retrieved private keys from 4,962 invalid signatures across 189 distinct RSA public keys. Though such errors are infrequent, hardware flaws make them unavoidable, offering exploitable opportunities, particularly in older TLS versions.Ĭontrary to earlier assumptions about SSH's resilience against this attack, the researchers demonstrated the extraction of RSA secrets using lattice-based attacks. This scenario enables the recovery of the private key. Errors in computation involving one prime factor might produce an invalid signature, potentially similar to the correct signature modulo another prime factor. The use of the Chinese Remainder Theorem (CRT) in RSA, aimed at faster decryption and reduced public key size, presents a potential vulnerability. The research, led by Keegan Ryan, Kaiwen He, Nadia Heninger, and George Arnold Sullivan, exposes faults in signature computation when using CRT-RSA, potentially allowing observers to calculate private keys from observed signatures. SSH, a widely used cryptographic network protocol for secure communication, relies on RSA, a public-key cryptosystem, for user authentication. This vulnerability reveals that, under specific circumstances, passive network attackers can extract secret RSA keys from errors occurring during failed SSH connection attempts. A collaborative study by researchers from universities in California and Massachusetts has uncovered a potential vulnerability affecting SSH (Secure Shell) connections.
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