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a letter to mcrypt maintainer (a weird observation) February 27, 2007

Posted by TSAI HONG-BIN in Diary.
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Dear mcrypt maintainer:

Thank you for maintaining this great work. It’s quite handy and powerful.
However, after running a quick benchmarking, I found that the
encryption/decryption speed of Rijndael (with key size both in 128
bits and 256 bits) is much slower than Twofish, CAST …etc. More
strangely, rijndael-128 is slower than rijndael-256. This isn’t
normal. So do you have any idea about this issue? The experiment
result is appened.

mcrypt -t -f key.256 -a rijndael-256 <data>
1st round (in seconds) 2M 16M 64M 256M
encryption                     0.152 1.192 4.71 23.195
decryption                     0.154 1.184 4.736 23.577

2nd round                      0.148 1.164 4.612 23.424
0.15 1.184 4.703 19.013

3rd round                     0.149 1.171 4.617 19.96
0.155 1.182 4.724 18.868

average                     0.149666667 1.175666667 4.646333333 22.193
0.153 1.183333333 4.721 20.486

mcrypt -t -f key.128 -a rijndael-128 <data>
1st round (in seconds) 2M 16M 64M
encryption                     0.184 1.241 4.975
decryption                     0.165 1.282 5.81

2nd round                     0.164 1.238 4.891
0.166 1.276 5.078

3rd round                     0.16 1.244 4.899
0.168 1.276 5.102

average                     0.16933 1.241 4.92167
0.16633 1.278 5.33

The encryption/decryption time of 16M data, using Twofish, is
approximately 0.5 second. 0.8 second if CAST is used.

Best regards,
Benjamin

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