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Security Fundamentals & Crypto · Foundational

Key Length

The size of a cryptographic key in bits, which determines the size of the key space and resistance to brute force.

Definition

Longer keys increase the number of possible keys exponentially, raising the work factor for brute-force attacks. Comparable strength varies by algorithm: a 128-bit symmetric key is roughly equivalent to a 3072-bit RSA key or a 256-bit elliptic curve key. NIST SP 800-57 and SP 800-131A provide current minimums.

Example

Moving from RSA-2048 to RSA-3072 raises security strength from about 112 bits to 128 bits.

Exam tip

Do not compare key lengths across algorithm types directly; ECC uses much shorter keys than RSA for equal strength.

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