区块链开发之生成12个助记词

我最近封装了一个库，使用起来更简单，大家可以移步这里：Bip44确定性算法的android实现
Java版的库：Bip44确定性算法的Java实现库(Android和java平台都可以使用)

这里添加一下SecureRandomUtils类的代码，
注：如果你引入了web3j的库，就不需要自己在项目中添加此类，手动添加此类，里面的LinuxSecureRandom类，可以使用bitcoinj库下的，具体路径为：org.bitcoinj.crypto.LinuxSecureRandom

这里使用bitcoinj库，来实现生成bip39的12个助记词，引用库

implementation ‘org.bitcoinj:bitcoinj-core:0.14.7’

填坑1

如果你直接引用库之后，直接安装运行apk，会造成app崩溃，这是因为这个库里面有一个libscrypt.dylib，这个库是针对x86_64平台的，并且没有其他平台的这个库，所以在arm cpu平台的手机app会崩溃，解决方案就是在gradle的android节点下，加上以下配置

 packagingOptions {
        exclude 'lib/x86_64/darwin/libscrypt.dylib'
        exclude 'com/google/thirdparty/publicsuffix/PublicSuffixPatterns.gwt.xml'
        exclude 'com/google/thirdparty/publicsuffix/PublicSuffixType.gwt.xml'
        exclude 'org/bitcoinj/crypto/mnemonic/wordlist/english.txt'
        exclude 'org/bitcoinj/crypto/cacerts'
    }

填坑2

我们要得到12个随机的单词，就要用到里面的MnemonicCode类，但是这个类，默认会new一个实例出来，并且默认加载的单词库路径方式是不支持android的，官方代码如下

   static {
        try {
            INSTANCE = new MnemonicCode();
        } catch (FileNotFoundException e) {
            // We expect failure on Android. The developer has to set INSTANCE themselves.
            if (!Utils.isAndroidRuntime())
                log.error("Could not find word list", e);
        } catch (IOException e) {
            log.error("Failed to load word list", e);
        }
    }

 /** Initialise from the included word list. Won't work on Android. */
    public MnemonicCode() throws IOException {
        this(openDefaultWords(), BIP39_ENGLISH_SHA256);
    }

    private static InputStream openDefaultWords() throws IOException {
        InputStream stream = MnemonicCode.class.getResourceAsStream(BIP39_ENGLISH_RESOURCE_NAME);
        if (stream == null)
            throw new FileNotFoundException(BIP39_ENGLISH_RESOURCE_NAME);
        return stream;
    }

可以从代码中看出来，在android平台此路径是绝对不可用的，所以我们要手动自己new这个对象，使用public MnemonicCode(InputStream wordstream, String wordListDigest) throws IOException, IllegalArgumentException这个构造函数

具体实现代码

    public static void generateMnemonic(Context context) throws Exception {
        MnemonicCode mnemonicCode = new MnemonicCode(context.getAssets().open("english.txt"), null);

        SecureRandom secureRandom = SecureRandomUtils.secureRandom();
        byte[] initialEntropy = new byte[16];//算法需要，必须是被4整除
        secureRandom.nextBytes(initialEntropy);
        List<String> wd = mnemonicCode.toMnemonic(initialEntropy);
        if (wd == null || wd.size() != 12)
            throw new RuntimeException("generate word error");
        else {
            words.clear();
            words.addAll(wd);
            LogUtils.d(words.toString());
        }
    }

SecureRandomUtils工具类

import java.security.SecureRandom;

/**
 * 如果你引入了web3j的库，就不需要自己在项目中添加此类，手动添加此类，里面的LinuxSecureRandom类，可以使用bitcoinj库下的，具体路径为：org.bitcoinj.crypto.LinuxSecureRandom
 * Utility class for working with SecureRandom implementation.
 *
 * 
This is to address issues with SecureRandom on Android. For more information, refer to the
 * following issue.
 */
final public class SecureRandomUtils {

    private static final SecureRandom SECURE_RANDOM;

    static {
        if (isAndroidRuntime()) {
            new LinuxSecureRandom();
        }
        SECURE_RANDOM = new SecureRandom();
    }

    public static SecureRandom secureRandom() {
        return SECURE_RANDOM;
    }

    // Taken from BitcoinJ implementation
    // https://github.com/bitcoinj/bitcoinj/blob/3cb1f6c6c589f84fe6e1fb56bf26d94cccc85429/core/src/main/java/org/bitcoinj/core/Utils.java#L573
    private static int isAndroid = -1;

    static boolean isAndroidRuntime() {
        if (isAndroid == -1) {
            final String runtime = System.getProperty("java.runtime.name");
            isAndroid = (runtime != null && runtime.equals("Android Runtime")) ? 1 : 0;
        }
        return isAndroid == 1;
    }

    private SecureRandomUtils() { }
}