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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?

  • 1
    define "normal computer" – schroeder Jun 20 '15 at 18:31
  • Normal computer in the sense consists some standard hardware which is virus free, normal behavior – Lokanath Jun 20 '15 at 18:32
  • I'm not sure how a virus would affect the algorithm. "Standard Hardware" is just as vague as "normal computer". – schroeder Jun 20 '15 at 18:36
  • Wow, chill out, am new here, but am quite sure a virus can affect algorithms – Lokanath Jun 20 '15 at 18:38
2

Roughly: For one i7-4750HQ core: 700MByte/s vs. 500MByte/s.

Source: https://calomel.org/aesni_ssl_performance.html

I suggest you check on your target hardware with the

openssl speed

command.

  • Thank you, one of the software(AIDA64) gives me 3526MBps for i5 cpu, is it accurate – Lokanath Jun 20 '15 at 11:39
  • @user78766 Maybe? Do you understand that even on your computer, each test will give you a different result? Benchmarking which makes sense can´t be done with one measurement. – deviantfan Jun 20 '15 at 13:22
  • The openssl utility does not necessarily use AES-NI, which makes a massive difference. – forest Dec 26 '17 at 14:03
2

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 :)

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