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A comment on Poisonous MD5 – Wolves Among the Sheep. Parent comment

Re:Poisonous MD5 – Wolves Among the Sheep by jimrandomh on Wednesday June 10, 2015 @01:17PM (#9693760)
No, the property you describe is called "preimage resistance". Collision resistance is stronger; it states that an attacker should not be able to create a pair of inputs with the same hash. In the case of md5, creating a pair of inputs with the same hash is easier than creating another input with the same hash as something else which you didn't yourself generate.

The MD5 algorithm is known to lack collision resistance, but whether it has preimage resistance is less certain; mathematical advances have weakened its preimage resistance, but not yet to the point of demonstrating a practical preimage attack.

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Re:Poisonous MD5 – Wolves Among the Sheep by garrettr_ on Wednesday June 10, 2015 @02:20PM (#9694252)
Nitpick: the property OP describes is actually second pre-image resistance, not preimage resistance (or collision resistance). See https://en.wikipedia.org/wiki/Cryptographic_hash_function#Pr...
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Re:Poisonous MD5 – Wolves Among the Sheep by kedean on Wednesday June 10, 2015 @02:00PM (#9694091)
My mistake, I always mixed those two up. Both properties address OP, though, as MD5 is not suspected to have preimage resistance either (it's just not to the point of somebody having done it yet).
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Re:Poisonous MD5 – Wolves Among the Sheep by 4mnt on Wednesday June 10, 2015 @01:42PM (#9693959)
> In the case of md5, creating a pair of inputs with the same hash is easier than creating another input with the same hash as something else which you didn't yourself generate.

This is the case with all instances of seeking a collision, due to the birthday paradox [0]

0: https://en.wikipedia.org/wiki/Birthday_attack

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Re:Poisonous MD5 – Wolves Among the Sheep by cstejerean on Wednesday June 10, 2015 @02:13PM (#9694204)
The birthday paradox helps with the case of finding any two random inputs that have the same hash. The problem with MD5 is that it's feasible to craft two specific inputs that happen to have the same hash.
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