Key Length Comparison
Compare cryptographic key lengths across algorithms for equivalent security strength.
Inputs
Security Strength
128-bit security
Symmetric (AES) Key
128bits
Equivalent RSA Key
3,072bits
Equivalent ECC Key
256bits
RSA/Symmetric Size Ratio
24.0
Step by step
Symmetric security level
AES-128
= 128-bit security
Equivalent RSA key size
NIST SP 800-57 table
= 3072 bits
Equivalent ECC key size
NIST SP 800-57 table
= 256 bits
RSA/Symmetric ratio
3072 / 128
= 24x
How it works
Different cryptographic algorithms achieve the same security strength with vastly different key sizes. RSA requires much longer keys than AES for equivalent security because its strength relies on the difficulty of factoring large numbers (sub-exponential attack) rather than brute-force search (exponential). ECC sits in between, offering compact keys with strong security.
Formula
NIST equivalence (approximate)
AES-128 ~ RSA-3072 ~ ECC-256 (128-bit security level)
- 128-bit security
- An attacker needs approximately 2^128 operations to break
Frequently Asked Questions
Why does RSA need such large keys compared to AES?
RSA's security depends on the difficulty of integer factoring, which has sub-exponential (not exponential) attack complexity. The Number Field Sieve algorithm can factor RSA keys much faster than brute force, so RSA needs disproportionately larger keys to maintain equivalent security against the best known attacks.
Is AES-256 twice as secure as AES-128?
In terms of brute-force keyspace, AES-256 has 2^128 times more keys than AES-128 (not twice as many). Both are considered unbreakable by brute force with current or foreseeable technology, but AES-256 provides a larger margin against potential future cryptanalytic advances or quantum computing threats.