Android下使用Openssl库

1.编译Openssl源代码，生成.so库（笔者使用环境为Ubuntu 18.04 amd64 桌面版，android_ndk_r19c 64位版）：

    下载Openssl源代码，进入源码环境然后运行配置脚本，设置编译参数，开始编译：    

    export ANDROID_NDK=/home/gj/android-ndk-r19c
    export PATH=/home/gj/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/bin:$PATH
    ./Configure android-arm shared
    make SHLIB_EXT=.so -j8

　　生成的.so保存一下。如果想生成其他ABI架构的so，可以clean后再配置、编译：

    make clean
    ./Configure android-arm64 shared
    make SHLIB_EXT=.so -j8

　　

2.新建Android项目（注意要选中Native C++这个。笔者使用环境为Android Studio 4.0，JDK1.8，gradle 6.1.1，gradle plugin 4.0.0），复制openssl源代码目录下所有头文件（include目录），以及上一步生成的所有.so到Android项目中。

项目地址：https://github.com/areful/NdkUseOpenssl

native-lib.cpp示例展示了如何使用openssl库进行RSA加解密、生成签名并验证签名。

代码太多，就不一一列出来内容了，可以clone代码查看内容，只列一下build.gradle和CMakeLists.txt主要内容：

build.gradle：

android {
    ......

    defaultConfig {
        ......

        externalNativeBuild {
            cmake {
                cppFlags "-std=c++11 -frtti -fexceptions"
                arguments '-DANDROID_STL=c++_shared'
            }
            ndk {
                stl = "c++_shared"
                abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
            }
        }
    }
    ......


    sourceSets {
        main {
            jniLibs.srcDirs = ['${PROJECT_SOURCE_DIR}/libs']
        }
    }

    packagingOptions {
        pickFirst '**/*.so'
    }

    externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }


}

　　CMakeLists.txt:

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

cmake_minimum_required(VERSION 3.4.1)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")

###############################################################
# import openssl library files BEGIN
include_directories(include)

set(SSL_LIB_NAME ssl)
add_library(${SSL_LIB_NAME} SHARED IMPORTED)
set_target_properties(${SSL_LIB_NAME} PROPERTIES IMPORTED_LOCATION ${PROJECT_SOURCE_DIR}/libs/${ANDROID_ABI}/lib${SSL_LIB_NAME}.so)

set(CRYPTO_LIB_NAME crypto)
add_library(${CRYPTO_LIB_NAME} SHARED IMPORTED)
set_target_properties(${CRYPTO_LIB_NAME} PROPERTIES IMPORTED_LOCATION ${PROJECT_SOURCE_DIR}/libs/${ANDROID_ABI}/lib${CRYPTO_LIB_NAME}.so)
# import openssl library files END
###############################################################

find_library(log-lib log)

add_library(native-lib SHARED
        native-lib.cpp
        native-lib.h
        b64/b64.cpp
        b64/b64.h
        b64/test_b64.cpp
        b64/test_b64.h
        rsa/rsa.cpp
        rsa/rsa.h
        rsa/test_rsa.cpp
        rsa/test_rsa.h
        common.h)

target_link_libraries(
        native-lib
        ssl
        crypto
        ${log-lib})