Android

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This document will provide instructions for building the OpenSSL library for Android devices. If you need the FIPS Validated Object Module and the FIPS Capable Library, see FIPS Library and Android.

Executive Summary

Use the following commands to build and install the OpenSSL library for Android. Before running the commands download openssl-1.0.1g.tar.gz and setenv-android.sh; place the files in the same directory (the 'root' directory mentioned below); ensure ANDROID_NDK_ROOT is set; and verify setenv-android.sh suites your taste. ANDROID_API and ANDROID_TOOLCHAIN will be set by the setenv-android.sh script. The files can be obtained from http://www.openssl.org/source/, http://openssl.com/fips/2.0/platforms/android/, and below (see Downloads section).

Prepare the OpenSSL Sources

# From the 'root' directory
$ rm -rf openssl-1.0.1g/
$ tar xzf openssl-1.0.1g.tar.gz
$ chmod a+x setenv-android.sh

Build the OpenSSL Library

# From the 'root' directory
$ . ./setenv-android.sh
$ cd openssl-1.0.1g/

# Perl is optional, and may fail in OpenSSL 1.1.0
$ perl -pi -e 's/install: all install_docs install_sw/install: install_docs install_sw/g' Makefile.org

# Tune to suit your taste, visit http://wiki.openssl.org/index.php/Compilation_and_Installation
$ ./config shared no-ssl2 no-ssl3 no-comp no-hw no-engine \
     --openssldir=/usr/local/ssl/$ANDROID_API --prefix=/usr/local/ssl/$ANDROID_API

$ make depend
$ make all

Install the OpenSSL Library

# The -E is important. Root needs some of the user's environment
$ sudo -E make install CC=$ANDROID_TOOLCHAIN/arm-linux-androideabi-gcc RANLIB=$ANDROID_TOOLCHAIN/arm-linux-androideabi-ranlib

Compile and Link against the Library

arm-linux-androideabi-gcc -I /usr/local/ssl/include my_prog.c -o my_prog.exe -L /usr/local/ssl/lib -lssl -lcrypto

OpenSSL Library

While the Executive Summary provided the whirlwind instructions for building and installing the OpenSSL library, this sections provides detailed instructions. There are six steps to building the OpenSSL Library for use in various projects, and they are listed below. Projects range from simple NDK based command line programs to Android activities using the JNI bridge.

  1. Acquire the required files
  2. Adjust the cross-compilation script
  3. Prepare the OpenSSL sources
  4. Build the OpenSSL Library
  5. Install the OpenSSL Library

Acquire the Required Files

First, obtain the base files from http://www.openssl.org/source/:

  • openssl-1.0.1g.tar.gz

Next, acquire the auxiliary files which can be obtained from below (see Downloads section) or http://openssl.com/fips/2.0/platforms/android/. You won't need all the files from the location.

openssl-1.0.1g.tar.gz is the OpenSSL Library. setenv-android.sh is used to set the cross-compilation environment.

After collecting the required files, your working directory will look similar to below. 

android-openssl $ ls -l 
-rw-r--r-- 1   4459777 Jun 15 03:32 openssl-1.0.1g.tar.gz
-rwxr-xr-x 1      6760 Jun 23 01:52 setenv-android.sh

Adjust the Cross-Compile Script

setenv-android.sh is used to set the cross-compilation environment. Open the script an ensure the following match your needs. If you are using android-ndk-r8e, android-14, and ANDROID_NDK_ROOT is set, then the script should be ready to use as-is.

  • _ANDROID_NDK – the version of the NDK. For example, android-ndk-r8e
  • _ANDROID_ARCH – the architecture. For example, arch-arm or arch-x86
  • _ANDROID_EABI – the version of the EABI tools. For example, arm-linux-androideabi-4.6, arm-linux-androideabi-4.8, x86-4.6 or x86-4.8
  • _ANDROID_API – the API level. For example, android-14 or android-18

You should also set ANDROID_SDK_ROOT and ANDROID_NDK_ROOT. The environmental variables are used internally by the Android platform tools and scripts. For details, see Recommended NDK Directory?.

Additional environmental variables which are set by setenv-android.sh and used by Configure and config include the following. You should not need to change them.

  • MACHINE – set to armv7
  • RELEASE – set to 2.6.37
  • SYSTEM – set to android
  • ARCH – set to arm
  • CROSS_COMPILE – set to arm-linux-androideabi-
  • ANDROID_DEV – set to $ANDROID_NDK_ROOT/platforms/$_ANDROID_API/arch-arm/usr
  • HOSTCC – set to gcc

Prepare the OpenSSL Sources

Remove stale versions of the OpenSSL Library, and then unpack fresh files. Also ensure the script is executable. 

$ rm -rf openssl-1.0.1g/
$ tar xzf openssl-1.0.1g.tar.gz
$ chmod a+x setenv-android.sh

Build the OpenSSL Library

This section of the document will guide you through the creation of the the OpenSSL Library. The OpenSSL Library (and Makefile.org) needs its install rule modified. The install rule includes the all target, which causes items to be built during install. A bug in the process when running as root results in an empty signature for the shared object (the signature is a string of zeros).

To build the OpenSSL Library, you must issue config, but other options are up to you. Some suggested options for configure include: shared, no-ssl2, no-ssl3, no-comp, no-hw, and no-engine. shared will build and install both the shared object and static archive. You should specify --openssldir to ensure the build system installs the android version of the library in a distinct location (other than /usr/local/ssl).

Begin building the OpenSSL library by setting the cross-compilation environment. Note the leading '.' when running the setenv-android.sh script. If you have any errors from the script, then you should fix them before proceeding. 

$ . ./setenv-android.sh
$ cd openssl-1.0.1g/

If you receive a meesage "Error: FIPS_SIG does not specify incore module, please edit this script, then its safe to ignore it. setenv-android.sh is used to build both the FIPS Capable OpenSSL library and the non-FIPS version of the library. FIPS_SIG is not needed in this configuration.

Next, fix the makefile and run configure. A user on Stack Overflow reports this fails under OpenSSL 1.1.0. If so skip it because its not essential to the cross-compile. 

$ perl -pi -e 's/install: all install_docs install_sw/install: install_docs install_sw/g' Makefile.org
$ ./config shared no-ssl2 no-ssl3 no-comp no-hw no-engine --openssldir=/usr/local/ssl/android-14/

Then run make depend and make all: 

$ make depend
$ make all

After make completes, verify libcrypto.a and libssl.a were built for the embedded architecture. 

$ find . -name libcrypto.a
./libcrypto.a
$ readelf -h ./libcrypto.a | grep -i 'class\|machine' | head -2
  Class:                   ELF32
  Machine:                 ARM

Install the OpenSSL Library

Finally, install the library. The makefile's install rule uses both CC and RANLIB, so you will need to fully specify the command variables on the command line (during install, sudo drops the user's path). You must also use sudo's -E option; otherwise ANDROID_TOOLCHAIN will be empty and tools such as arm-linux-androideabi-gcc and arm-linux-androideabi-ranlib will not be found. 

$ sudo -E make install CC=$ANDROID_TOOLCHAIN/arm-linux-androideabi-gcc RANLIB=$ANDROID_TOOLCHAIN/arm-linux-androideabi-ranlib

Compile and Link against the Library

Install the OpenSSL Library placed the cross-compiled library in /usr/local/ssl. To link against it, you must perform the following: 

arm-linux-androideabi-gcc -I /usr/local/ssl/include my_prog.c -o my_prog.exe -L /usr/local/ssl/lib -lssl -lcrypto

The above only tells you how to specify the OpenSSL library. You will still need to include system headers and libraries, or use --sysroot to supply the information.

Testing the OpenSSL Library

Testing the installation consists of building a sample program, installing it with adb, and then running the program using a remote shell. Both the static and dynamic version of the OpenSSL library can be tested. Instructions for testing the OpenSSL library are given at FIPS Library and Android. The same basic steps apply.

Wrapper Shared Objects

Using OpenSSL on Android often involves JNI and the platform's version of OpenSSL or BoringSSL. The platform likely loaded the system's version of libssl.so and libcrypto.so at boot during Zygote initialization. Due to issues with the loader and symbol resolution, customary LD_LIBRARY_PATH tricks do not work for most applications. And changing the build to output different library names, like libmyssl.so and libmycrypto.so, to avoid clashes does not work either.

The solution to the namespace and symbol resolution problems is to wrap the static version of the OpenSSL library in a separate dynamic library or shared object provided by you. To do so, write a small C wrapper library with references to functions you need from the OpenSSL library. You don't need to wrap all the functions.

Your wrapper.c might look as follows (also see GCC's Visibility page): 

#if __GNUC__ >= 4
    #define DLL_PUBLIC __attribute__ ((visibility ("default")))
    #define DLL_LOCAL  __attribute__ ((visibility ("hidden")))
#else
    #define DLL_PUBLIC
    #define DLL_LOCAL
#endif
    
DLL_PUBLIC void My_OpenSSL_add_all_algorithms() {
   
    return (void)OpenSSL_add_all_algorithms();
}
    
DLL_PUBLIC void My_SSL_load_error_strings() {

    return (void)SSL_load_error_strings();
}

...

Then, compile the source file into a shared object. A typical command line might look as follows. 

$ export OPENSSL_ANDROID = /usr/local/ssl/android-14
$ $(CC) wrapper.c -fPIC -shared -I$(OPENSSL_ANDROID)/include -fvisibility=hidden -Wl,--exclude-libs,ALL \
-Wl,-Bstatic -lcrypto -lssl -L$(OPENSSL_ANDROID)/lib -o wrapper.so -Wl,-Bdynamic

-fvisibility=hidden works as you expect, and -Wl,--exclude-libs,ALL means your library does not re-export other linked library symbols. Only the functions marked with DLL_PUBLIC will be exported and callable through JNI.

The -Wl,-Bstatic tells the linker to use the static version of the OpenSSL library for the Library. After it and the -Wl,-Bdynamic tells the linker to use dynamic linking for anything else it might need, like libc.

Then use your shared object in place of OpenSSL.

Miscellaneous

The following lists some miscellaneous items we are aware.

Position Independent Code

The NDK supplies headers for each major platform - for example, API 18, API 14, API 9, API 8, and API 5. If you are building for Android 4.2 (API 17), Android 4.1 (API 16) and Android 4.0 (API 14), then you would use the NDK's API 14 (android-14 platform).

Specify the full library name when calling Java's System.load. That is, call System.load(“libcrypto.so.1.0.0”). Also note that some Android routines expect the prefix of “lib” and suffix of “so”, so you might have to rename the library.

Some versions of the Android Java system loader will load the system's version of the OpenSSL library, even though you built and included a copy with your application. In this case, you might need to write a wrapper shared object and link to the static version of the OpenSSL library. See, for example, "Unable to find native library" error in Native Activity app.

If you compile with -fPIE and -pie, then you will core dump unless using Android 4.1 and above. Logcat shows the linker (/system/bin/linker) is the problem. 

shell@android: $ ./fips_hmac.exe -v fips_hmac.exe
[2] + Stopped (signal)     ./fips_hmac.exe -v fips_hmac.exe
[1] - Segmentation fault   ./fips_hmac.exe -v fips_hmac.exe

When building the OpenSSL library for Android, take care to specify -mfloat-abi=softfp. If you specify -mfloat-abi=hard or -mhard-float (even if the hardware support a floating point unit), then the entropy estimate passed through the Java VM to RAND_add will always be 0.0f. See Hard-float and JNI for details.

Static Library Linking

Using -Bstatic and -Bshared can cause link problems on occasion. For example, see Android: error when trying to compile wrapper for openssl library libcrypto.a. To avoid the problem with the linker, specify the full path to the static archive (for example, /usr/local/ssl/android-14/lib/libcrypto.a). If you suspect the wrong OpenSSL library is being linked, then use the fully qualified archive path.

Downloads

setenv-android.sh - script to set Android cross-compile environment.

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