Hacker News new | comments | show | ask | jobs | submit login Announcing the first SHA-1 collision ( googleblog.com ) 2174 points by pfg 9 hours ago | hide | past | web | 421 comments | favorite nneonneo 5 hours ago The visual description of the colliding files, at http://shattered.io/static/pdf_format.png , is not very helpful in understanding how they produced the PDFs, so I took apart the PDFs and worked it out. Basically, each PDF contains a single large (421,385-byte) JPG image, followed by a few PDF commands to display the JPG. The collision lives entirely in the JPG data - the PDF format is merely incidental here. Extracting out the two images shows two JPG files with different contents (but different SHA-1 hashes since the necessary prefix is missing). Each PDF consists of a common prefix (which contains the PDF header, JPG stream descriptor and s...