Which hashing algorithm is considered the most secure?

A. MD5
B. SHA-1
C. SHA-256
D. CRC32

Answer: C. SHA-256
Explanation:

Understanding Hashing Algorithms

In the world of the CISSP, hashing is synonymous with Integrity. A cryptographic hash function takes an input (or 'message') and returns a fixed-size string of bytes. The output, often called a "fingerprint" or "message digest," should be unique to that specific input.

1. SHA-256 (Secure Hash Algorithm 2)

SHA-256 is part of the SHA-2 family designed by the NSA. It produces a 256-bit (32-byte) signature.

• Why it’s the standard: It is currently the industry benchmark for digital signatures, SSL/TLS certificates, and blockchain technology. It provides a high level of collision resistance, meaning it is computationally infeasible to find two different inputs that produce the same output.

• CISSP Context: When the exam asks for a secure, modern hashing standard, SHA-256 (or its larger sibling SHA-512) is almost always the correct choice.

2. SHA-1 (The Deprecated Standard)

SHA-1 produces a 160-bit digest. While it was the king of hashing for years, it is now considered cryptographically broken.

• The Vulnerability: Researchers have successfully performed "collision attacks" against SHA-1. Because of this, browser vendors and federal agencies have phased it out in favor of SHA-2 or SHA-3.

3. MD5 (Message Digest 5)

MD5 creates a 128-bit hash. It was designed for speed, but that speed is now its downfall.

• The Vulnerability: MD5 is extremely susceptible to "collision" and "pre-image" attacks. Using modern hardware, an attacker can generate a collision in seconds.

• Usage Today: It should only be used for non-security tasks, such as verifying that a file wasn't corrupted during a standard download (checksums).

4. CRC32 (Cyclic Redundancy Check)

CRC32 is not a cryptographic hash function; it is a parity bit/checksum used primarily in network traffic (Ethernet) and storage devices.

• The Difference: CRC32 is designed to detect accidental changes caused by network noise or hardware glitches. It has no mathematical protection against a malicious actor who wants to change data and recalculate the checksum to match.

The 5 Properties of a Secure Hash

For a hashing algorithm to be useful in a security context (like SHA-256), it must meet these criteria:

1. Deterministic: The same input always produces the same output.

2. Quick Computation: It must be fast to generate a hash for any given data.

3. Pre-Image Resistance: It should be impossible to "reverse" a hash to find the original input.

4. Small Changes = Big Difference: (The Avalanche Effect) Changing a single bit in the input should radically change the hash output.

5. Collision Resistance: It must be nearly impossible to find two different inputs that result in the same hash.

CISSP Study Rule of Thumb

• Insecure/Legacy: MD5, SHA-1.

• Secure/Current: SHA-256, SHA-512, SHA-3.

• Not for Security: CRC32 (it's just a checksum).

The "CISSP Rule of Thumb": If you see MD5 or SHA-1, think Legacy/Insecure. If you see SHA-2 (like 256 or 512) or SHA-3, think Current Standard.