Key Length Comparison
Compare cryptographic key lengths across algorithms for equivalent security strength.
About Key Length Comparison
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
Worked example
With the default values below, Key Length Comparison returns Security Strength of 128-bit security. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Symmetric Key Length (AES)one of 128-bit (AES-128), 192-bit (AES-192), 256-bit (AES-256)
- 128-bit (AES-128)
Results
- Security Strength
- 128-bit security
- Symmetric (AES) Key
- 128 bits
- Equivalent RSA Key
- 3,072 bits
- Equivalent ECC Key
- 256 bits
- RSA/Symmetric Size Ratio
- 24.0
Step by step
- 1Symmetric security level= 128-bit security
- 2Equivalent RSA key size= 3072 bits
- 3Equivalent ECC key size= 256 bits
- 4RSA/Symmetric ratio= 24x
Assumptions and limits
- The result is derived only from the single input listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.