A symmetric cipher with a 256-bit key has approximately how many possible keys?
A CISSP practice question covering Domain 3: Security Architecture and Engineering. Try answering before reading the explanation below.
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Why "2^256" is the right answer
An n-bit key has 2^n possible values, so a 256-bit key has 2^256 possibilities. AES-256 is considered post-quantum resistant by symmetric standards because Grover's algorithm only halves the effective key length to 2^128 — still enormous.
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