Why develop new stream ciphers when block ciphers can be trivally made into streams?

Question

I've just been reading about a new drop-in replacement for the RC4 stream cipher, but why develop new stream ciphers when AES can be made into a stream with a little XORing?

score 5 · Accepted Answer · answered Oct 30 '14 at 17:10

5

The biggest reason is performance. Stream ciphers are generally faster than block ciphers and perform fewer operations. Stream ciphers only need to generate a pseudorandom output while block ciphers need to be pseudorandom permutations. So when you create a steam cipher out of a block cipher, you are doing a lot more work to get the same effect. To get an idea, look at how much more work is required to encrypt 16 bytes with AES than RC4.

answered Oct 30 '14 at 17:10

user13741

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Comparing dissimilar ciphers like AES and RC4 is pretty difficult. On large modern CPUs AES will be much faster. – CodesInChaos Oct 30 '14 at 19:11
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On small modern CPUs for embedded systems, RC4 will be hilariously faster – Richie Frame Oct 30 '14 at 20:53
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@CodesInChaos: Only with the special instructions - AES-NI. – Nova Oct 30 '14 at 21:33

Why develop new stream ciphers when block ciphers can be trivally made into streams?

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