(add) Android implementation

android/build.gradle

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+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion 26
+    buildToolsVersion "26.0.1"
+
+    defaultConfig {
+        minSdkVersion 19
+        targetSdkVersion 22
+        versionCode 1
+        versionName "1.0"
+    }
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+        }
+    }
+}
+
+dependencies {
+    compile 'com.android.support:appcompat-v7:23.0.1'
+    compile 'com.facebook.react:react-native:+'
+    compile 'com.madgag.spongycastle:core:1.58.0.0'
+    compile 'com.madgag.spongycastle:prov:1.54.0.0'
+    compile 'com.madgag.spongycastle:pkix:1.54.0.0'
+    compile 'com.madgag.spongycastle:pg:1.54.0.0'
+}

android/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="rnpbkdf2">
+</manifest>

android/src/main/java/rnpbkdf2/PBKDF2.java

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+package pbkdf2;
+
+import android.widget.Toast;
+
+import java.io.IOException;
+import java.security.SecureRandom;
+import java.util.HashMap;
+import java.util.Map;
+
+import java.util.UUID;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.spec.InvalidKeySpecException;
+import java.security.InvalidKeyException;
+
+import java.nio.charset.StandardCharsets;
+
+import javax.crypto.Cipher;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.SecretKeySpec;
+import javax.crypto.spec.IvParameterSpec;
+import javax.crypto.spec.PBEKeySpec;
+import javax.crypto.SecretKeyFactory;
+import javax.crypto.Mac;
+
+import org.spongycastle.crypto.digests.SHA512Digest;
+import org.spongycastle.crypto.generators.PKCS5S2ParametersGenerator;
+import org.spongycastle.crypto.params.KeyParameter;
+import org.spongycastle.util.encoders.Hex;
+
+import android.util.Base64;
+
+import com.facebook.react.bridge.NativeModule;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.Promise;
+import com.facebook.react.bridge.ReactContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+import com.facebook.react.bridge.Callback;
+
+public class PBKDF2 extends ReactContextBaseJavaModule {
+
+    private static final Integer SHA512_DIGEST_LENGTH = 512;
+
+    public PBKDF2(ReactApplicationContext reactContext) {
+        super(reactContext);
+    }
+
+    @Override
+    public String getName() {
+        return "PBKDF2";
+    }
+
+    @ReactMethod
+    public void derivationKey(String pwd, String salt, Integer iterations, Promise promise) {
+        try {
+            String strs = pbkdf2(pwd, salt, iterations, SHA512_DIGEST_LENGTH);
+            promise.resolve(strs);
+        } catch (Exception e) {
+            promise.reject("-1", e.getMessage());
+        }
+    }
+
+    public static String bytesToHex(byte[] bytes) {
+        final char[] hexArray = "0123456789abcdef".toCharArray();
+        char[] hexChars = new char[bytes.length * 2];
+        for ( int j = 0; j < bytes.length; j++ ) {
+            int v = bytes[j] & 0xFF;
+            hexChars[j * 2] = hexArray[v >>> 4];
+            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
+        }
+        return new String(hexChars);
+    }
+
+    private static String derivationKey(String pwd, String salt, Integer cost, Integer length)
+    throws NoSuchAlgorithmException, InvalidKeySpecException
+    {
+        PKCS5S2ParametersGenerator gen = new PKCS5S2ParametersGenerator(new SHA512Digest());
+        gen.init(pwd.getBytes(StandardCharsets.UTF_8), salt.getBytes(StandardCharsets.UTF_8), cost);
+        byte[] key = ((KeyParameter) gen.generateDerivedParameters(length)).getKey();
+        return bytesToHex(key);
+    }
+}

android/src/main/java/rnpbkdf2/PBKDF2Package.java

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+package rnpbkdf2;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import com.facebook.react.ReactPackage;
+import com.facebook.react.bridge.JavaScriptModule;
+import com.facebook.react.bridge.NativeModule;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.uimanager.ViewManager;
+
+import rnpbkdf2.PBKDF2;
+
+public class PBKDF2Package implements ReactPackage {
+    @Override
+    public List<NativeModule> createNativeModules(ReactApplicationContext reactContext) {
+        return Arrays.<NativeModule>asList(
+                new PBKDF2(reactContext)
+        );
+    }
+
+    public List<Class<? extends JavaScriptModule>> createJSModules() {
+        return Collections.emptyList();
+    }
+
+    @Override
+    public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) {
+        return Arrays.<ViewManager>asList();
+    }
+}