!!! Overview
[{$pagename}] happens when two distinct pieces of [data] render the same [Hash] digest.

[{$pagename}], in practice, should never occur for [Secure Hash Algorithms]. 

However if the [Secure Hash Algorithms] has some flaws, as [SHA-1] does, a well-funded attacker can craft a [{$pagename}]. 

The [attacker] could then use this [{$pagename}] to deceive systems that rely on hashes into accepting a [malicious] file in place of its benign counterpart. 

!! [SHA-1] [{$pagename}] [Example][1]
For example, two insurance contracts with drastically different terms.

[Cryptographic Collision/Collision-illustrated.png]


Here are some numbers that give a sense of how large scale this [Computational Hardness Assumption] was:
* Nine __quintillion__ (9,223,372,036,854,775,808) [SHA-1] computations in total
* 6,500 years of CPU computation to complete the attack first phase
* 110 years of GPU computation to complete the second phase

While those numbers seem very large, the [SHA-1] shattered attack is still more than 100,000 times faster than a [Brute-Force] [attack] which remains impractical.


!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [https://shattered.it/|https://shattered.it/|target='_blank'] - based on information obtained 2017-02-24-