What does 2^256 represent in the context of SHA-256?

• A. Number of inputs for a 256-bit output
• B. Number of possible hash values for a 256-bit hash
• C. Size of the hash
• D. Probability of a collision

Answer: (B)

SHA-256 produces a 256-bit hash, so there are 2^256 possible outputs. Each bit can be 0 or 1, giving a vast space of distinct hash values. This is the size of the output space—the number of different hash values the function can produce—not the number of inputs you can feed into it, which can be far larger and is not fixed. It’s also not the actual length of the hash in bytes (the hash is 32 bytes, i.e., 256 bits). The probability of a collision is a separate concept and is not represented by 2^256 itself; it’s related to how likely two random inputs produce the same 256-bit output, which is extremely small for a single pair and becomes more significant only when hashing many inputs (captured by the birthday bound). Therefore, 2^256 best represents the number of possible hash values for a 256-bit hash.