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Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could anyone explain how this conversion is calculated?

Thanks.

gal
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    You have not provided sufficient information. Firstly, different implementations of both algorithms have different speed. Secondly, what RSA padding is used? Thirdly, what size of the RSA modulus is assumed? Fourthly, what is the length of the plain text to be encrypted? – Henrick Hellström Mar 11 '13 at 14:37
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    Of related interest. – mikeazo Mar 11 '13 at 14:42
  • None of that information was given to complete the exercise, so I assumed it had to be possible with just that information. I suppose I could make some assumptions about it. – gal Mar 11 '13 at 14:57
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    In addition to Henrick's questions, there's also the question of whether we're talking about RSA encryption or RSA decryption speed; those differ radically. – poncho Mar 11 '13 at 15:19
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    "convert an RSA speed in bytes per second to a DES speed in bytes per second" makes as much sense as "convert a tractor speed in meter per second to a jet speed in meter per second". – fgrieu Mar 11 '13 at 15:26
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    Find some website with benchmarks (or create your own). If the cost is given per-operation, instead of per-byte, then divide by the block size in bytes. – CodesInChaos Mar 11 '13 at 15:28
  • See: http://wiki.openwrt.org/inbox/benchmark.openssl. Scroll down to "Comparison to other common systems". DES has a number around 30,000,000 and RSA has a number around 80 for sign and around 3,000 for verify. Couldn't see quickly what those numbers are, but that site might be a good starting place. – mikeazo Mar 11 '13 at 17:18
  • The speed difference should be very noticable on a CPU platform. So your professor is likely not interested in precise numbers. To compare speed: openssl command line has performance related functionality. For fun, also generate a high security RSA key pair (16 Kib) and see how long that takes. – Maarten Bodewes Mar 11 '13 at 18:01
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    The question makes no sense. You don't encrypt the same type of data with RSA or DES, the comparison is meaningless. Why should you care that RSA is "100 times slower than DES"? You're not going to be encrypting megabytes of data with it. It's a useless metric, things like "encryptions/signatures/verifications per second" are much more sensible. – Thomas Mar 12 '13 at 05:16
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    @Thomas: the question does make sense, if the reason the professor chose this exercise was to show why we didn't just encrypt everything with RSA directly. – poncho Mar 12 '13 at 20:12

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