Question 1

What is a hash function?

Accepted Answer

A hash function takes an input (or message) and returns a fixed-size string of bytes. The output (hash) is unique to each unique input. Even a small change in the input produces a completely different hash. Hash functions are one-way — you cannot reverse a hash to find the original input.

Question 2

What is the difference between MD5, SHA-1, and SHA-256?

Accepted Answer

MD5 produces a 128-bit hash (32 hex characters), SHA-1 produces a 160-bit hash (40 hex characters), and SHA-256 produces a 256-bit hash (64 hex characters). SHA-256 is the most secure of the three. MD5 and SHA-1 are considered cryptographically broken and should not be used for security purposes.

Question 3

Is MD5 still safe to use?

Accepted Answer

MD5 is not safe for security purposes like password hashing or digital signatures because collisions can be generated. However, it is still commonly used for non-security purposes like checksums to verify file integrity or as a quick fingerprint for data deduplication.

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