[cryptography] Announcing the first SHA1 collision

Jeffrey Walton noloader at gmail.com
Sat Feb 25 15:55:04 EST 2017


Cryptographic hash functions like SHA-1 are a cryptographer’s swiss
army knife. You’ll find that hashes play a role in browser security,
managing code repositories, or even just detecting duplicate files in
storage. Hash functions compress large amounts of data into a small
message digest. As a cryptographic requirement for wide-spread use,
finding two messages that lead to the same digest should be
computationally infeasible. Over time however, this requirement can
fail due to attacks on the mathematical underpinnings of hash
functions or to increases in computational power.

Today, more than 20 years after of SHA-1 was first introduced, we are
announcing the first practical technique for generating a collision.
This represents the culmination of two years of research that sprung
from a collaboration between the CWI Institute in Amsterdam and
Google. We’ve summarized how we went about generating a collision
below. As a proof of the attack, we are releasing two PDFs that have
identical SHA-1 hashes but different content.

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