Gaëtan Leurent
More info
- Affiliation
- Inria, Paris
- Known for
- Sweet32, SHA-1 is a Shambles
French cryptanalyst who makes theoretical weaknesses cheap enough that nobody can keep calling them theoretical.
In 2016 Leurent and Karthikeyan Bhargavan used Sweet32 to show that 64-bit block ciphers such as 3DES and Blowfish were dangerous in long-lived HTTPS and OpenVPN sessions. The maths was a plain birthday attack, known for decades; the news was that a few hundred gigabytes of traffic sufficed.
In 2020 he and Thomas Peyrin took the next step against SHA-1. Where SHAttered had produced an identical-prefix collision three years earlier, SHA-1 is a Shambles delivered a chosen-prefix collision for about US$45,000 of rented GPU time, demonstrated with two PGP keys sharing one certification. GnuPG stopped accepting new SHA-1-based identity signatures at the same time.