Decryption slower in 1.1.1 branch?

Viktor Dukhovni openssl-users at
Tue Jan 28 20:34:27 UTC 2020

On Tue, Jan 28, 2020 at 06:24:06PM +0000, Dan Heinz wrote:

> >RSA is not intended for bulk data decryption, its intended uses are
> >key transport and signing.  Bulk data decryption is done via AES or
> >similar.

It sounds like you're directly encrypting data with RSA.  That's a
mistake.  RSA is for decrypting a symmetric algorithm key, that then
decrypts the data.

> >Are you sure that's seconds and not milliseconds?  These are absurdly
> >long times, almost certainly dominated by factors other than the
> >encryption algorithms.  On my 2015 laptop (MacOS) I get:
> Yes, it is seconds.  

Sorry, 0.6 seconds for a single 1024-bit RSA_private_decrypt() (128
bytes of data) is not plausible, but you say you have just over 8KB of
data, which would take ~65 calls to RSA_private_decrypt() to decrypt
piecewise.  It sure looks like you're measuring something other than
what you claim to be measuring, or not describing it accurately.

    OpenSSL 1.1.1c-dev  xx XXX xxxx
    options:bn(64,64) rc4(16x,int) des(int) aes(partial) idea(int) blowfish(ptr)
                      sign    verify    sign/s verify/s
    rsa 1024 bits 0.000135s 0.000013s   7414.8  78566.9

On my laptop RSA_private_decrypt (aka sign) takes 135 microseconds.  You
claim 600 milliseconds for perhaps ~60 calls, which might be 10ms each,
but that still is about two orders of magnitude too slow.

So, sorry whatever you're measuring, it is not the performance of

> While I'm ok with the execution speed with OpenSSL 1.0.2, I'd like to
> figure out why the times doubled with OpenSSL 1.1.1.  

Neither is a reasonable performance level, but also it is not reasonable
to use RSA for bulk data encryption.

> I'm logging times before and after the calls to RSA_private_decrypt.

How many calls?  What else is happening to feed the data into the
decryption algorithm, and reassemble the output?

> With OpenSSL 1.0.2 it takes on average about 4-8 milliseconds for each
> RSA_private_decrypt call.  With OpenSSL 1.1.1d, it takes 10-15
> milliseconds for each RSA_private_decrypt call.

Now we see that you're in fact chunking data for multiple calls to
"decrypt" via RSA.  That's a fatal design flaw. This is not a valid
operating mode for RSA.  You MUST NOT do this.

> >> I'm wondering if perhaps my build configuration is incorrect or 
> >> missing something for the 1.1.1d build.  Here are the configuration 
> >> parameters for the 64-bit build:

You have a deeper problem, your use of RSA is broken.

> The data being decrypted is local on the client machine and is just an XML file. 
> RSA key is 1024 bits.  
> I'm using OAEP padding.

This is a mistake, for asymmetric encryption you should be using CMS.

> Thank you for the information.  I removed it from the configuration
> parameters.  I didn't really notice a difference in execution time
> though.  I also removed the no-asm parameter, setup nasm, and rebuilt
> with no noticeable changes.  

Likely the time is dominated by something other than the RSA operations,
but since those are mistake anyway, it hardly matters.

> > I logged things granular enough to see the speed difference was in 
> > RSA_private_decrypt, but I'm not sure why it is so much slower with 
> > 1.1.1d.  Any help or ideas would be appreciated!

STOP.  Fix your design to use CMS.  Report any performance differences
in CMS between 1.0.2 and 1.1.1 when built correctly with asm support.

> >At 600ms for 8KB, it is not plausible that the time is spend doing
> >cryptography.  That's barely fast enough to feed a 1980's modem.
> I would expect the execution times to be more in line with what I saw
> with Linux for both 1.0.2 and 1.1.1.  But even so, I do not understand
> why just upgrading to 1.1.1 causes the RSA_private_decrypt calls to
> double in execution time from what they were with 1.0.2?

I would expect execution times that are 2 to 3 orders of magnitude
faster, especially if you were using sound cryptographic primitives.


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