Why is MD5 considered insecure?

• A. It is no longer considered secure
• B. It is quantum-unsafe
• C. It provides perfect secrecy
• D. It is too slow for practical use

Answer: (A)

MD5 is insecure because it’s not collision-resistant. Researchers have shown practical methods to generate two different inputs that yield the same MD5 digest, which means an attacker can substitute tampered data, forged certificates, or altered messages without changing the hash. This breaks the integrity guarantees that hashing is supposed to provide in signatures, certificates, and file checksums, so MD5 is no longer trusted for security-critical use. The other options miss the point: MD5 isn’t primarily a quantum vulnerability, hashing isn’t about perfect secrecy, and MD5 is actually very fast to compute, not slow.