Re: [lwip-users] Building mbedtls using LWIP library :: Handshake takes too long

[Antonio Gonga]

Hi Noam,

Thanks for your answer.

>>Do you use any external SDRAM or just the M3 own memory ?.

I do not have an external SDRAM yet. My application still uses the Demos /programs/ssl/ssl_server/client, which I believe is fairly simple. and need not much memory.

>>Have you been able to run the SSL server demo from mbedTLS ?

I am using the Demo examples. The connection is established, the handshake is what takes too much time.

The LWIP layer works since I can see TCP connection establishment messages on wireshark, and also the initial handshake messages.

once again thanks, I will keep debugging. 

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Best Regards,
/António, KTH Royal Institute of Technology/Sweden

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From: lwip-users <lwip-users-bounces+address@hidden> on behalf of Noam Weissman <address@hidden>
Sent: Thursday, June 8, 2017 15:09
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Building mbedtls using LWIP library :: Handshake takes too long

 

Hi,

 

Do you use any external SDRAM or just the M3 own memory ?... If you do not have any extra RAM

I do not see how you can run HTTPS.. you need around 100-200K RAM to run HTTPS for one page.

The estimate is based that your page hase one or more JS files, one or more images, one or more

CSS files… in all you need 4-6 connections to load a single page and that needs lots of RAM.

 

Every SSL connection needs 16K for receive and 16K for transmit + some overhead. If you tweak

mbedTLS and use a smaller send buffer you may save on RAM but still need about 20+K RAM for

a connection… multiply that by 4-6 that’s a lot.

 

As for hardware acceleration… some M3 have DES, AES, SHA, CRC and RNG engines. This may help but

It is not related to big numbers, as far as I understand.

 

Have you been able to run the SSL server demo from mbedTLS ?... If not then I suggest first run the demo

And then work on your own code.

 

Good luck,

Noam.

 

From: lwip-users [mailto:lwip-users-bounces+address@hidden On Behalf Of antonio
Sent: Thursday, June 08, 2017 10:31 AM
To: address@hidden
Subject: Re: [lwip-users] Building mbedtls using LWIP library :: Handshake takes too long

 

Hi all, I am trying to port mbedTLS to work with my embedded device. My problem is that the handshake procedure never completes, therefore, I am unable to have any HTTPS communication. Further debugging, I noticed that the math computations are taking too long (bignum.c). Is there a way to avoid such a mess ? I am using MC "arm-cortex-m3", which I believe can achieve fast computations. Any kind of optimizations etc is kindly welcome. /Antonio

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