use libcryto.so and libssl.so in an android project?

Question

I\'m beginer to Android NDK. I want to build a RSA example base on openssl libary. First, I built libssl.so and libcrypto.so librairies with ndk-build in the guardianproje

Answer 1

I'm beginer to Android NDK. I want to build a RSA example base on openssl libary.

You can, but you have to be careful. Here's the reason Alex told you to use static libraries for libssl and libcrypto in your script.

The master Android process is zygote. Its like init in Linux. Zygote loads OpenSSL when its start, and it loads version 0.9.8. If you link against OpenSSL 1.0.1, then you will get mysterious runtime crashes. The crashes are due to the Android loader using the 0.9.8 version of the library (already mapped from Zygote), and not your version of OpenSSL.

You can use a shared object, but your shared object must be a wrapper around the static version of libssl and libcrypto.

If you are not using Android's build system, then you can find additional instructions for building purely from the command line at OpenSSL's wiki. The wiki page includes setting the envrionment and cross compiling. See FIPS Library and Android.

Another thing to watch out for: be sure to build with -mfloat-abi=softfp. The stock OpenSSL misses that when cross compiling. You need it to ensure floats are passed on the stack, and not through floating point registers. Otherwise, all your floats will mysteriously have 0.0f value (like the floats used to estimate entropy in RAND_add).