# Tag Info

### Why can't we reverse hashes?

Take a simple mathematical operation like addition. Addition takes 2 inputs and produces 1 output (the sum of the two inputs). If you know the 2 inputs, the output is easy to calculate - and there's ...
• 2,154

### How do hashes really ensure uniqueness?

The simple answer is that hashes don't ensure uniqueness. Very broadly, hashes behave like "deterministic random numbers" – deterministic in the sense that hashing the same data always ...
• 1,211
Accepted

### Second pre-image resistance vs Collision resistance

The difference is in the choice of $m_1$. In the first case (second preimage resistance), the attacker is handed a fixed $m_1$ to which he has to find a different $m_2$ with equal hash. In particular,...
• 10.9k
Accepted

### How can hashes be unique if they are limited in number?

how can for example SHA-256 be unique if there is only a limited number of them?! Where your issue occurs is that they're not unique. It's just very improbable that they'll reoccur. Unique in ...
• 13.8k

• 122k
Accepted

### What are the consequences of removing a single byte from a sha256 hash?

Does this bias the hash in any way? We want the avalanche criteria on the output bits, that is a change in the any of input bit must randomly affect half of the output bits. Each bit of the hash ...
• 42.9k
Accepted

### What makes SHA-256 secure?

It's worth pointing out that in the case of SHA2 and most other hashes the compression function has a block cipher (keyed permutation) as its core. Basically what you are asking is identical to ...
• 246

### Are there two known strings which have the same MD5 hash value?

Two different strings in hex format: ...
• 587
Accepted

### What is hardened SHA-1, how does it work and how much protection does it offer?

Hardened SHA-1 detects collisions built of a certain form, If someone were to find a collision using brute-force birthday attack (currently not feasible) the detection would not work. The vectors are ...
• 10.4k
Accepted

### Is using a broken SHA-1 for password hashing secure?

SHA-1 in itself was never safe for password hashing. The hash algorithm itself doesn't have a work factor parameter nor does it have a salt as input. These are requirements for run-of-the-mill ...
• 84.5k

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