What is the time taken by an AES Encryption algorithm, with a key of 128 bits, operating on a normal computer (say with Intel i7) and what will be the impact be on the time if I wish to use a 256 bit key?
Roughly: For one i7-4750HQ core: 700MByte/s vs. 500MByte/s.
I suggest you check on your target hardware with the
If you are wondering where that difference in encryption/decryption speed comes from, it's quite easy: AES uses different number of encryption rounds depending on key length.
For 128 bit keys it does 10 rounds, for 192 bit keys it does 12 rounds and for 256 bit keys it does 14 rounds.
So, AES-256 will typically be 40% slower than AES-128 (provided that encryption speed is bounded by CPU and not I/O). Note that this aligns perfectly with benchmarks provided by @StackzOfZtuff :)