Benchmarking AES and RC2 from Openssl - why AES is faster?

Question

I wrote a simple code in pure C to benchmark AES-CBC-256 and RC2-CBC-128 from Openssl. My testing loops look like this:

for(i=0; i<tests; i++) { timer_start(); for(j=0; j<its; j++) { RC2_cbc_encrypt(input, enc_out, length, &key, iv_enc, RC2_ENCRYPT); } stop = timer_stop(); printf("%f\n",(stop / its) * 1000); } for(i=0; i<tests; i++) { timer_start(); for(j=0; j<its; j++) { AES_cbc_encrypt(input, enc_out, length, &enc_key, iv_enc, AES_ENCRYPT); } stop = timer_stop(); printf("%f\n",(stop / its) * 1000); }

But something wrong is happening, on every machine I test my code I get strange results, that is, every time AES is faster than RC2. What could be the problem? I use getrusage to measure time (in my timers).

AES: 0.010898 0.010471 0.010531 RC2: 0.023261 0.023392 0.023224

Also check this answer, the paragraph just before the last paragraph. — Maarten Bodewes
– Maarten Bodewes, Commented Dec 3, 2014 at 21:05

user149341 · Accepted Answer · 2014-12-03 21:02:23Z

3

Nothing is wrong. AES is faster because:

RC2 is rather complex, from a computational perspective.
AES has been optimized heavily in software, because it is so frequently used.
Some CPUs have hardware acceleration for AES (e.g. AES-NI for x86).

answered Dec 3, 2014 at 21:02

user149341

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5 Comments

yak Over a year ago

Hmm, and how about 3DES? Should it be faster than RC2 but slower than AES? It seemed strange to me because when I tested it with Openssl, I got 283758 for AES and 205444 for RC2 and was sure that it was me who did the mistake in my code, not the Openssl programmers. Could you be so kind and answer about 3DES and 2 others? Thank you :)

user149341 Over a year ago

DES is also rather complex, is difficult to implement in software, and is not hardware-accelerated on most systems. That result sounds reasonable to me.

yak Over a year ago

So why In Openssl AES in slower than RC2 and in my code is faster than RC2? I tested it with openssl speed on the same machine I tested my code

Maarten Bodewes Over a year ago

That sentence doesn't make sense. Besides I think duskwuff correctly answered your question already.

user149341 Over a year ago

You're reading the results wrong. The numbers printed by openssl speed are the number of iterations it completed per second — higher numbers from this tool mean it's faster, not slower.

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