IAI, TCG CREST is proud to announce that Sougata Mandal successfully defended his PhD thesis, “Provable Security of Symmetric Key Modes in Ideal Cipher Model,” on 31st July, 2026.
The thesis studies the provable security of symmetric key modes in the ideal cipher model, aiming to understand fundamental limits and design efficient constructions that achieve strong security. Sougata proposed new tweakable block ciphers achieving optimal security for large tweaks while minimizing structural overhead, and extended these results to forkciphers, obtaining the first provably secure constructions with optimal security in the ideal cipher model.
His work also examined leakage-resilient authenticated encryption based on tweakable block ciphers and forkciphers. For Grade-2 schemes, he established tight bounds on the minimum tweak length required for ciphertext integrity under leakage, and proposed a rate-efficient construction achieving maximal security with reduced tweak size. For Grade-3 schemes, he introduced the first forkcipher-based construction achieving beyond-birthday-bound security, along with a low-latency variant suitable for practical settings.
The thesis further investigates committing security for AEAD and MAC, identifying structural conditions under which leakage-resilient AEAD achieves committing security, and analyzing several beyond-birthday-bound MAC constructions under multiple committing notions to reveal inherent limitations and structural trade-offs.
Overall, the work provides tight bounds, optimal constructions, and new insights into the design of symmetric key modes in the ideal cipher model.
Sougata has 9 publications to his name, including work at top cryptology conferences such as Eurocrypt and Asiacrypt, and in reputed journals including IACR Transactions on Symmetric Cryptology and IACR Communications in Cryptology. He also holds a single-author publication in IACR Communications in Cryptology.
Congratulations to Sougata on this significant achievement!
