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to get highest performance Which asymmetric cipher provide fastest encryption/decryption ? ECC or DH ? what key size is recommended today ?

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This can change drastically based on hardware support and the particular implementation you choose. When in doubt, benchmark. –  Stephen Touset Mar 25 '13 at 21:24
    
@Stephen Touset cryptopp.com/benchmarks.html seems RSA is fastest ?! ECC 13.20 RSA 1.46 –  rsa Mar 26 '13 at 8:19
    
@rsa RSA is fast for encryption but really slow for decryption. You're comparing different security levels and you're not looking at a good ECC implementation. –  CodesInChaos Mar 26 '13 at 8:22
    
Are you talking about bulk encryption/decryption of large amounts of data? Or are you talking about large *numbers) of encryption/decryption operations of small amounts of data? (If the former, I think you don't understand how asymmetric ciphers are used.) –  David Schwartz Mar 26 '13 at 12:56
    
@rsa When in doubt, benchmark on your own hardware with the implementations you have available. If performance is important, nobody can answer this question except for you. –  Stephen Touset Mar 26 '13 at 17:50
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1 Answer

up vote 3 down vote accepted

I prefer a ~128 bit security level. With ECC this means a curve with ~256 bits, with DH or RSA this corresponds to around 3000 bits. If you can accept a lower security level, the advantage of ECC over DH/RSA gets smaller.

My favourite is Curve25519, which has easily available high performance implementations. An alternative is P256 which is a NIST standard, but a bit slower. There are also some other curves/implementations which are faster than Curve25519, but those seem more academic.

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perfect answer thank you –  rsa Mar 26 '13 at 20:23
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