3553x's Blog About Cryptography, Security and Other Things

IND-CPA Security & Deterministic Stateless Encryption

17. Feb, 2021

Encryption algorithms which for a given key always map the same message to the same ciphertext (i.e. deterministic, stateless algorithms) are not IND-CPA secure. This is typically taught in introductory level courses on cryptography, however I noticed that some students seem to be confused about this and every now and then a question about this pops up on online discussion forums. Hence, I have written this blogpost in hopes of clearing things up.

Breaking AES128 with Multi-Bit DPA

25. Aug, 2019

This post is about how I attempted to implement Paul Kocher’s well known Differential Power Analysis (DPA) attack by attacking AES128. The attack didn’t work out initially and I had to use my creativity to rediscover a variation of the attack, namely Multi-Bit DPA, which has already been known for years. Ultimately, I managed to implement a DPA attack that can recover the encryption key with nothing but the ciphertext, power traces of the encryption device and a few hours of time.