A few days ago, a new attack has been made public which makes it easier to forge hash (or “message digests”) computed with SHA1 (see for example this article for more details).

This new collision attack makes it faster and less expensive to create two documents with the same digital signature using SHA1 or, having a digitally signed document where the digital signature uses SHA1 as hash algorithm, to create a different second document which has the same digital signature.

It has been known since a few years that SHA1 is broken and that it should not be used for digital signatures and in general for security purposes (actually NIST suggested to stop using SHA1 already in 2012). But as usual, in the real world there are still many, too many legacy applications which today continue to use SHA1, one example being legacy PGP keys and old PGP digital signatures.

This new result should be at least a useful reminder to all of us to check if we are still using SHA1 in some applications and in case finally update it.