Collision resistance

In cryptography, collision resistance is a property of cryptographic hash functions: a hash function H is collision-resistant if it is hard to find two inputs that hash to the same output; that is, two inputs a and b where a ≠ b but H(a) = H(b). ... Those functions are called provably secure.

1. Why is collision resistance desirable for hash functions?
2. What is weak collision and strong collision resistance?
3. What is collision in Crypto?
4. What is the difference between second preimage resistance and collision resistance?
5. How do you test a hash collision?
6. How is SHA-256 Collision resistant?
7. Is hashing collision resistant?
8. What are collisions in hashing?
9. How Mac is different than hash?
10. Is PRGS collision-resistant?
11. Do all hashes have collisions?
12. What happens after hash collision?
13. What is the difference between weak and strong collision resistance in a hash function?
14. What is 2nd preimage resistance?
15. What is the effectiveness of a 128 bit hash value?

Why is collision resistance desirable for hash functions?

Collision resistance is important when you're relying on hash functions to always map two inputs to two different values, like in the content-addressable storage example above.

What is weak collision and strong collision resistance?

Weak collision resistance (CR), or second-preimage resistance, is the property that given x and h(x) (h a hash function) it's difficult to find x′≠x such that h(x′)=h(x). Strong CR, or just collision resistance, is the property that it's difficult to find any two x,x′ with the same hash value.

What is collision in Crypto?

In cryptography, a collision attack on a cryptographic hash tries to find two inputs producing the same hash value, i.e. a hash collision. This is in contrast to a preimage attack where a specific target hash value is specified.

What is the difference between second preimage resistance and collision resistance?

The properties of second preimage resistance and collision resistance may seem similar but the difference is that in the case of second preimage resistance, the attacker is given a message to start with, but for collision resistance no message is given; it is simply up to the attacker to find any two messages that ...

How do you test a hash collision?

For the test itself, take your sample input values, hash each one and put the results into a set. Count the size of the resulting set and compare it to the size of the input set, and this will tell you the number of collisions your hash function is generating.

How is SHA-256 Collision resistant?

If these are all equally probable, then it would take approximately 5 billion attempts (5.38 × 10⁹) to generate a collision using brute force. ... Since executing a brute-force attack of this size is considered computationally infeasible, SHA-256 can be considered collision-resistant, for now at least.

Is hashing collision resistant?

Collision resistance is the property of a hash function that it is computationally infeasible to find two colliding inputs. This property is related to second preimage resistance, which is also known as weak collision resistance.

What are collisions in hashing?

Definition: A collision occurs when more than one value to be hashed by a particular hash function hash to the same slot in the table or data structure (hash table) being generated by the hash function. ... This is a collision.

How Mac is different than hash?

The main difference is conceptual: while hashes are used to guarantee the integrity of data, a MAC guarantees integrity AND authentication.

Is PRGS collision-resistant?

BMY-PRG is the most efficient known construction, whose security relies on a reasonable assumption. ... In this paper, we investigate a question of finding an efficient hash-function-based PRG, whose security relies on collision-resistance, a very well-studied and widely-used property of a hash function.

Do all hashes have collisions?

Every hash function with more inputs than outputs will necessarily have collisions.

What happens after hash collision?

In computer science, a hash collision or clash is when two pieces of data in a hash table share the same hash value. ... Although hash algorithms have been created with the intent of being collision resistant, they can still sometimes map different data to the same hash (by virtue of the pigeonhole principle).

What is the difference between weak and strong collision resistance in a hash function?

Strong And Weak Collision Resistance Are Not The Same

Even though they seem similar, there is a subtle difference between strong and weak collision resistance. Weak collision resistance is bound to a particular input, whereas strong collision resistance applies to any two arbitrary inputs.

What is 2nd preimage resistance?

Second preimage resistance is the property of a hash function that it is computationally infeasible to find any second input that has the same output as a given input. ... Second preimage resistance is also known as weak collision resistance.

What is the effectiveness of a 128 bit hash value?

What is the effectiveness of a 128 bit hash value? Explanation: In most normal text files, the high order bit of each octet is always zero. So if a 128 bit hash value is used, instead of an effectiveness of 2^-128, the hash function will have an effectiveness of 2^-112.