Question 1

What is MD5?

Accepted Answer

MD5 (Message Digest Algorithm 5) is a cryptographic hash function designed by Ron Rivest in 1991. It produces a 128-bit (32 hex character) hash value. MD5 is still widely used for file checksums and non-security deduplication, but is not safe for password storage or digital signatures due to known collision vulnerabilities.

Question 2

Why is MD5 deprecated for passwords?

Accepted Answer

MD5 is extremely fast — GPUs can compute billions of MD5 hashes per second — making it trivial to brute-force weak passwords. MD5 also has collision vulnerabilities where different inputs produce the same hash. Use bcrypt, Argon2, or scrypt for password storage.

Question 3

What is the difference between MD5 and SHA-256?

Accepted Answer

MD5 produces 128-bit (32 hex char) output; SHA-256 produces 256-bit (64 hex char) output. MD5 has known collision attacks; SHA-256 has none. SHA-256 is recommended for any security-sensitive application. MD5 remains acceptable only for non-security purposes like file checksums and cache busting.

Question 4

Where is MD5 still safe to use?

Accepted Answer

MD5 is still safe for non-cryptographic uses: verifying file downloads where the hash source is trusted, database deduplication (finding identical files or records), cache key generation, and legacy system compatibility where security is not a concern.

Question 5

What is a hash collision in MD5?

Accepted Answer

A collision is when two different inputs produce the same MD5 hash. MD5 collisions can be generated in seconds on modern hardware. This means an attacker could craft a malicious file that has the same MD5 as a legitimate file. For file integrity verification of security software, use SHA-256.

Question 6

How do I migrate from MD5 to a secure hash?

Accepted Answer

For password storage: use bcrypt or Argon2 — rehash all passwords on next login by accepting the old MD5 hash as a temporary credential, immediately rehashing with bcrypt. For file checksums: replace MD5 with SHA-256 (same workflow, stronger output). For deduplication: SHA-256 is a drop-in replacement.

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