Key length considerations

Selecting appropriate cryptographic key lengths requires balancing security requirements with computational overhead. The following considerations should guide implementation decisions:

• Key length security characteristics:

• Security strength increases exponentially with bit length - a 2048-bit RSA key provides significantly higher security than a 1024-bit key

• Computational requirements increase proportionally with key length, affecting system performance

• Security margin increases logarithmically - doubling key length provides exponentially more possible combinations

• Common implementation error: Implementing maximum key lengths for all applications without considering performance implications

• Two types of cryptographic relationships:

• Symmetric: Same key locks and unlocks (AES, etc.)

  • Like having one key that works on both sides of your door

  • Blazingly fast compared to asymmetric encryption

  • The problem: How do you securely share that key with other parties without exposing it during transmission

• Asymmetric: Different keys for locking and unlocking (RSA, DSA, etc.)

  • Like a safety deposit box where you have one key and the bank has another

  • Significantly slower (think 1000x or more) than symmetric encryption

  • But solves the key distribution problem brilliantly

  • This is what we’re focusing on in this document

• Size limits that will bite you:

  • RSA can only encrypt messages smaller than your key size (minus padding)

  • A 2048-bit key can’t encrypt a 2048-bit message - more on this particular trap later

  • If you try to encrypt something too large, you’ll get an error that explains absolutely nothing.