CODEWITHSUNDEEP
hashcryptography
Y M
Y M

Reputation: 107

Why is SHA-1 considered insecure?

Microsoft, google and mozilla have decided not to accept it in 2017 because of the flaws found by researchers. And I saw SHA-1 is depreciated nearly everywhere simply because people think that it's not safe anymore. But unlike MD5, currently there is no known collision found on SHA-1. And even the fastest algorithm for the collision of SHA-1 still requires nearly 2^60 evaluations, which is still a very large number.

My question is why SHA-1, a hash algorithm which hasn't been found any collisions and which still requires a large amount of time to find a collision, is depreciated? I understand SHA-2 is more secure, but it is also slower than SHA-1, why most people recommend to trade performance for the so-called "security" where the security of SHA-1 is not even an issue for most situations?

Upvotes: 4

Views: 5884

Answers (1)

aaa
aaa

Reputation: 96

SHA-1 is weak because of collision attacks:

https://en.wikipedia.org/wiki/SHA-1#Attacks

In an interview, Yin states that, "Roughly, we exploit the following two weaknesses: One is that the file preprocessing step is not complicated enough; another is that certain math operations in the first 20 rounds have unexpected security problems."

https://www.schneier.com/blog/archives/2005/02/sha1_broken.html

collisions in the the full SHA-1 in 2^69 hash operations, much less than the brute-force attack of 2^80 operations based on the hash length.

collisions in SHA-0 in 2^39 operations.

collisions in 58-round SHA-1 in 2^33 operations.

there is a collision attack on SHA-1's compression function that requires only 2^57 SHA-1 evaluations

Upvotes: 6

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