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This question already has an answer here:

No SHA-1 collisions are actually known, though there are a number of cryptographic attacks to weaken it.

But, how likely is it that, of all the SHA-1 hashes computed since the invention of the algorithm, there has been a collision?

Not sure how to approach this, but it probably involves the Birthday Problem?

(if there's a better SE to ask this in, let me know)

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marked as duplicate by e-sushi Nov 26 '16 at 17:57

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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In order for a collision to happen "by chance", about $2^{80}$ hashes need to have been computed. If 1000 hashes were computed every millisecond, then this would take 38,334,786,263 years. So, I doubt that this has happened by chance.

Having said that, I would be very surprised if large government organizations do not already have SHA collisions (using better collision finding algorithms).

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