2021/11/12 by Jean Paul Degabriele, Jérôme Govinden, Felix Günther +1 · 25 citations
Computer Science · Mathematics · #Coding theory and cryptography #Computer science #Computer security #Cryptographic Implementations and Security #Cryptographic nonce #Cryptography #Cryptography and Data Security #Encryption #Matching (statistics) #Mathematics #Rekeying #Security analysis #Set (abstract data type) #Statistics #Theoretical computer science #Upper and lower bounds
paper · doi:10.1145/3460120.3484814
openalex publication_date 2021/11/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
The ChaCha20-Poly1305 AEAD scheme is being increasingly widely deployed in practice. Practitioners need proven security bounds in order to set data limits and rekeying intervals for the scheme. But the formal security analysis of ChaCha20-Poly1305 currently lags behind that of AES-GCM. The only extant analysis (Procter, 2014) contains a flaw and is only for the single-user setting. We rectify this situation. We prove a multi-user security bound on the AEAD security of ChaCha20-Poly1305 and establish the tightness of each term in our bound through matching attacks. We show how our bound differs both qualitatively and quantitatively from the known bounds for AES-GCM, highlighting how subtle design choices lead to distinctive security properties. We translate our bound to the nonce-randomized setting employed in TLS 1.3 and elsewhere, and we additionally improve the corresponding security bounds for GCM. Finally, we provide a simple yet stronger variant of ChaCha20-Poly1305 that addresses the deficiencies highlighted by our analysis.