Purpose built light-weight alternative to SSL/TLS?

Target hardware is a rather low-powered MCU (ARM Cortex-M3 @72MHz, with just about 64KB SRAM and 256KB flash), so walking the thin line here. My board does have ethernet, and I will eventually get lwIP (lightweight TCP/IP FOSS suite) running on it (currently struggling). However, I also need some kind of super light-weight alternative to SSL/TLS. I am aware of the multiple GPL'd SSL/TLS implementations for such MCU's, but their footprint is still fairl开发者_JAVA技巧y significant. While they do fit-in, given everything else, don't leave much room for others.

My traffic is not HTTP, so I don't have to worry about HTTPS, and my client/server communication can be completely proprietary, so non-standard solution is okay. Looking for suggestions on what might be the minimalistic yet robust (well a weak security is worthless), alternative that helps me --

1. Encrypt my communication (C->S & S->C)
2. Do 2-way authentication (C->S & S->C)
3. Avoid man-in-middle attacks

I won't be able to optimize library at ARMv7 assembly level, and thus bank entirely on my programming skills and the GNU-ARM compiler's optimization. Given above, any pointers of what might be the best options ?

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If any of those small TLS implementations allow you to disable all X.509 and ASN.1 functionality and just use TLS with preshared-keys you'd have quite a small footprint. That's because only symmetric ciphers and hashes are used.

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There's CurveCP. It's meant to completely replace SSL.

It's fairly new, and still undergoing development, but its author is a well-known expert in the field, and has been carefully working toward it during the past decade. A lot of careful research and design has been put into it.

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My immediate reaction would be to consider Kerberos. It's been heavily studied, so the chances of major holes at this point are fairly remote. At the same time, it's fairly minimalist, so unless you restrict what you need to do, you're probably not going to be able to use anything much more lightweight without compromising security.

If that's still too heavy for your purposes, you're probably going to need to impose some restrictions on what you want done.

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You might have a look at MST (Minimal Secure Transport) https://github.com/DiplIngFrankGerlach/MST.

It provides the same security assurances as TLS, but requires a pre-shared key. Also, it is very small (less than 1000 LoC, without AES) and can therefore easily be reviewed by an expert.

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I know it is to come with variant of answer about two years later, yet... "PolarSSL's memory footprint can get as small as 30k and averages below 110k." https://polarssl.org/features