Randomness of random in Cisco ASA — Arnaud Ebalard, Ryad Benadjila
Date : 07 June 2023 à 15:45 — 30 min.
It all started with ECDSA nonces and keys duplications in a large amount of X.509 certificates generated by Cisco ASA security gateways, detected through TLS campaigns analysis.
After some statistics and blackbox keys recovery, it continued by analyzing multiple firmwares for those hardware devices and virtual appliances to unveil the root causes of these collisions. It ended up with keygens to recover RSA keys, ECDSA keys and signatures nonces.
The current article describes our journey understanding Cisco ASA randomness issues through years, leading to CVE-2023-20107 [CVE-2023-20107, CSCvm90511]. More generally, it also provides technical and practical feedback on what can and cannot be done regarding entropy sources in association with DRBGs and other random processing mechanisms.