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Is SHA-1 collision resistant?
The National Security Agency published SHA-1 (SHA stands for Secure Hash Algorithm) in 1995 as a standard for cryptographically secure hashing. Designed to be collision resistant up to 280 bits, SHA-1 has had a long and useful life, and a collision has not been published as of this blog post.
Why is hash collision bad?
If you can generate hash collisions you can make it appear that someone digitally signed a document that they did not in fact sign. That’s bad, very bad. The irony is that hash collisions are inevitable, as a hash maps an infinite space to a finite space. In fact, there must be an infinite number of collisions.
What is the best that can be the techniques to avoid a collision?
We can avoid collision by making hash function random, chaining method and uniform hashing.
Why are SHA-1 collision attacks now actually practical?
“SHA-1 is also widely supported to authenticate TLS and IKE handshake messages. Now, what protocol can be attacked and to what extent is hard to tell at the moment, because it needs careful scrutiny of the inner working of the protocol and how the digital signatures/certificates are used, etc..
How does Google’s SHA-1 collision finder work?
On a basic level, the collision-finding technique involves breaking the data down into small chunks so that changes, or disturbances, in one set of chunks is countered by twiddling bits in other chunks. A disturbance vector [ PDF] is used to find and flip the right bits. A description of Google’s SHA-1 colliding PDFs can be found here.
Is there a collision attack for MD5 hashes?
At least one large scale collision attack is known to have already happened for MD5 hashes. But on Feb. 27th, 2017, Google announced SHAttered, the first-ever crafted collision for SHA-1. Google was able to create a PDF file that had the same SHA-1 hash as another PDF file, despite having different content. SHAttered was performed on a PDF file.
How is a disturbance vector used in SHA-1?
A disturbance vector [ PDF] is used to find and flip the right bits. A description of Google’s SHA-1 colliding PDFs can be found here. We note that the files essentially each contain a large JPEG, and the hash collision is focused on that image data.