Yahoo discloses hack of 1B accounts

Re:Yahoo discloses hack of 1B accounts by manarth on Wednesday December 14, 2016 @07:27PM (#13181136)

  > "Passing the password through MD5 reduces the complexity to 128 bits, you can't get that back."

Assuming that the new hash is secure (and sha512 is generally agreed to be secure), then, given a specific sha512 hash, the original MD5 hash can only be determined via rainbow tables, which is a Big-O operation. Even though entropy is reduced, it's still a significant work to determine the original MD5 hash (significant in this instance being longer than the heat-death of the Sun, given current extrapolations of computing performance).

Attacks against MD5 are based around knowing the original MD5 hash. In this instance, the original MD5 hash is unknown, so there is no mathematical shortcut to finding a collision.

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Re:Yahoo discloses hack of 1B accounts by leereeves on Wednesday December 14, 2016 @07:30PM (#13181161)

In this case an attacker isn't looking for a collision (which would mean creating two passwords with the same hash, and what hash that is doesn't matter).

The attacker needs a password with a specific hash, and the best reported attack for that is around 2^128.

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Re:Yahoo discloses hack of 1B accounts by manarth on Wednesday December 14, 2016 @07:40PM (#13181234)

Agreed, that the best reported rainbow-table attack on MD5 is 2^128 (i.e. the complete range of possible MD5 hashes).

Personally, I'm willing to chance that my password will be discovered via a brute-force attack within the next 0.65 billion billion years [1]

[1] http://bitcoin.stackexchange.com/questions/2847/how-long-wou...

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Re:Yahoo discloses hack of 1B accounts by leereeves on Wednesday December 14, 2016 @08:29PM (#13181545)

I think it does make sense to be cautious.

A new preimage attack could be discovered - or might already have been, secretly.

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