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Commonly confused · Security Fundamentals & Crypto

AES vs RSA: What's the Difference?

AES is a symmetric block cipher used to encrypt bulk data quickly, while RSA is an asymmetric algorithm based on factoring large primes, used for key exchange and digital signatures. They usually work together rather than compete.

AES

vs
AESRSA
TypeSymmetricAsymmetric
Key sizes128, 192, or 256 bitsCommonly 2048 to 4096 bits
Math basisSubstitution-permutation networkDifficulty of factoring large integers
SpeedVery fast, hardware acceleratedSlow, impractical for large data
Primary useEncrypting data at rest and in transitKey exchange, signatures, certificates
Quantum outlookAES-256 considered quantum resistantBroken by a large-scale quantum computer (Shor's algorithm)
Remember it

AES moves the data; RSA moves the key.

Exam tip

If a question asks for the best choice to encrypt a large database or full disk, pick AES. If it asks how two strangers securely share that AES key, RSA or Diffie-Hellman is the answer.

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