Question 1

What is a hash?

Accepted Answer

A hash is a fixed-size string of characters produced by a mathematical function from input data of any size. Hash functions are one-way: you cannot reverse a hash to get the original data. They are used for data integrity verification, password storage, digital signatures, and checksums.

Question 2

SHA-256 vs MD5 - which should I use?

Accepted Answer

SHA-256 is more secure and should be preferred for security-sensitive applications. MD5 is considered cryptographically broken and should not be used for security purposes. MD5 is still used for non-security checksums (file verification) due to its speed. SHA-256 produces a 256-bit (64 character) hash while MD5 produces 128-bit (32 character).

Question 3

Are hashes reversible?

Accepted Answer

No, cryptographic hash functions are designed to be one-way. You cannot reverse a hash to get the original input. However, attackers use rainbow tables and brute force to find inputs that produce a known hash. This is why passwords should use salted hashes with slow algorithms like bcrypt or Argon2.

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