区块链-ETH解锁钱包

本篇文章承接区块链-ETH创建钱包 , 基本概念在上篇文章中已经做了概要 , 现在我们开始说明分别通过助记词,私钥,Keystore来解锁钱包.

为了良好的阅读体验, 请阅读原文

环境

依赖环境还是BIP全家桶

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implementation 'io.github.novacrypto:BIP44:0.0.3'
// implementation 'io.github.novacrypto:BIP32:0.0.9' //存在少许问题
implementation 'com.lhalcyon:bip32:1.0.0' // 上面的BIP32有少许问题,笔者做了一些修改,已经上传lib
implementation 'io.github.novacrypto:BIP39:0.1.9'

助记词解锁钱包

校验助记词

对用户输入的助记词需要进行校验

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// validate mnemonic
try {
MnemonicValidator.ofWordList(English.INSTANCE).validate(mnemonics);
} catch (InvalidChecksumException e) {
e.printStackTrace();
} catch (InvalidWordCountException e) {
e.printStackTrace();
} catch (WordNotFoundException e) {
e.printStackTrace();
} catch (UnexpectedWhiteSpaceException e) {
e.printStackTrace();
}

解锁钱包

助记词解锁其实与创建钱包过程一致,只是增加了校验重复钱包的逻辑

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public Flowable<HLWallet> importMnemonic(Context context,
String password,
String mnemonics) {
Flowable<String> flowable = Flowable.just(mnemonics);

return flowable
.flatMap(s -> {
ECKeyPair keyPair = generateKeyPair(s);
WalletFile walletFile = Wallet.createLight(password, keyPair);
HLWallet hlWallet = new HLWallet(walletFile);
if (WalletManager.shared().isWalletExist(hlWallet.getAddress())) {
return Flowable.error(new HLError(ReplyCode.walletExisted, new Throwable("Wallet existed!")));
}
WalletManager.shared().saveWallet(context, hlWallet);
return Flowable.just(hlWallet);
});
}

私钥解锁钱包

私钥解锁/导入钱包的过程也与创建时大体一致

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public Flowable<HLWallet> importPrivateKey(Context context,
String privateKey,
String password) {
if (privateKey.startsWith(Constant.PREFIX_16)) {
privateKey = privateKey.substring(Constant.PREFIX_16.length());
}
Flowable<String> flowable = Flowable.just(privateKey);
return flowable.flatMap(s -> {
byte[] privateBytes = Hex.decode(s);
ECKeyPair ecKeyPair = ECKeyPair.create(privateBytes);
WalletFile walletFile = Wallet.createLight(password, ecKeyPair);
HLWallet hlWallet = new HLWallet(walletFile);
if (WalletManager.shared().isWalletExist(hlWallet.getAddress())) {
return Flowable.error(new HLError(ReplyCode.walletExisted, new Throwable("Wallet existed!")));
}
WalletManager.shared().saveWallet(context, hlWallet);
return Flowable.just(hlWallet);
});
}

Keystore解锁钱包

Keystore解锁钱包需要重点来讲

直接先上代码

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public Flowable<HLWallet> importKeystoreViaWeb3j(Context context, 
String keystore,
String password) {
return Flowable.just(keystore)
.flatMap(s -> {
ObjectMapper objectMapper = new ObjectMapper();
WalletFile walletFile = objectMapper.readValue(keystore, WalletFile.class);
ECKeyPair keyPair = Wallet.decrypt(password, walletFile);
HLWallet hlWallet = new HLWallet(walletFile);

WalletFile generateWalletFile = Wallet.createLight(password, keyPair);
if (!generateWalletFile.getAddress().equalsIgnoreCase(walletFile.getAddress())) {
return Flowable.error(new HLError(ReplyCode.failure, new Throwable("address doesn't match private key")));
}

if (WalletManager.shared().isWalletExist(hlWallet.getAddress())) {
return Flowable.error(new HLError(ReplyCode.walletExisted, new Throwable("Wallet existed!")));
}
WalletManager.shared().saveWallet(context, hlWallet);
return Flowable.just(hlWallet);
});
}

其过程主要是通过 WalletFile / Keystore + Password 得到 EcKeyPair 接着得到其他信息,主要API为

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ECKeyPair keyPair = Wallet.decrypt(password, walletFile);

增加了校验钱包是否已存在,以及Keystore是否与私钥匹配的逻辑

看似过程那么完美,其实当真正运用中就会发现程序走到这里经常OOM!

报错信息截取如下:

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at org.spongycastle.crypto.generators.SCrypt.SMix(SCrypt.java:143)
at org.spongycastle.crypto.generators.SCrypt.MFcrypt(SCrypt.java:87)
at org.spongycastle.crypto.generators.SCrypt.generate(SCrypt.java:66)
at org.web3j.crypto.Wallet.generateDerivedScryptKey(Wallet.java:136)
at org.web3j.crypto.Wallet.decrypt(Wallet.java:214)

进一步调试发现,是因为当N过大时,

org.spongycastle.crypto.generators.SCrypt.SMix(..)方法里的 124 行左右

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for (int i = 0; i < N; ++i)
{
V[i] = Arrays.clone(X);
...
}

这里不停地clone,导致了内存溢出Crash . 说到这里,不得不说一下创建钱包时,我们的选择

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Wallet.createLight(password, keyPair)

这里使用的是创建轻量级钱包,其原始调用为

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public static WalletFile create(String password, ECKeyPair ecKeyPair, int n, int p)

这里的N ,P 是可以自定义赋值的,其意义可自行google下.简单地来说,N越大,钱包加密程度越高.

当我们创建钱包是调用的createLight(...) , 而从 imToken 创建的钱包是采用的自定义大于我们’轻量’的标准的,因此从 imToken中创建的钱包导出Keystore,再在我们的钱包中导入,调用上述web3j的 Wallet.decrypt(...) 基本会OOM Crash.

可以在 web3j Issues 中搜到大量相关的问题 , 解答基本是说依赖库不兼容Android导致的 . 这里就减少道友们绕圈子的时间了,直接提供个可行的解决方案.

Link: Out Of Memory exception when using web3j in Android

就是我们需要修改部分方法.

OOM优化

这里需要依赖

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implementation 'com.lambdaworks:scrypt:1.4.0'

然后修改解密方法

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public static ECKeyPair decrypt(String password, WalletFile walletFile)
throws CipherException {

validate(walletFile);

WalletFile.Crypto crypto = walletFile.getCrypto();

byte[] mac = Numeric.hexStringToByteArray(crypto.getMac());
byte[] iv = Numeric.hexStringToByteArray(crypto.getCipherparams().getIv());
byte[] cipherText = Numeric.hexStringToByteArray(crypto.getCiphertext());

byte[] derivedKey;


if (crypto.getKdfparams() instanceof WalletFile.ScryptKdfParams) {
WalletFile.ScryptKdfParams scryptKdfParams =
(WalletFile.ScryptKdfParams) crypto.getKdfparams();
int dklen = scryptKdfParams.getDklen();
int n = scryptKdfParams.getN();
int p = scryptKdfParams.getP();
int r = scryptKdfParams.getR();
byte[] salt = Numeric.hexStringToByteArray(scryptKdfParams.getSalt());
// derivedKey = generateDerivedScryptKey(password.getBytes(Charset.forName("UTF-8")), salt, n, r, p, dklen);
derivedKey = com.lambdaworks.crypto.SCrypt.scryptN(password.getBytes(Charset.forName("UTF-8")), salt, n, r, p, dklen);
} else if (crypto.getKdfparams() instanceof WalletFile.Aes128CtrKdfParams) {
WalletFile.Aes128CtrKdfParams aes128CtrKdfParams =
(WalletFile.Aes128CtrKdfParams) crypto.getKdfparams();
int c = aes128CtrKdfParams.getC();
String prf = aes128CtrKdfParams.getPrf();
byte[] salt = Numeric.hexStringToByteArray(aes128CtrKdfParams.getSalt());

derivedKey = generateAes128CtrDerivedKey(
password.getBytes(Charset.forName("UTF-8")), salt, c, prf);
} else {
throw new CipherException("Unable to deserialize params: " + crypto.getKdf());
}

byte[] derivedMac = generateMac(derivedKey, cipherText);

if (!Arrays.equals(derivedMac, mac)) {
throw new CipherException("Invalid password provided");
}

byte[] encryptKey = Arrays.copyOfRange(derivedKey, 0, 16);
byte[] privateKey = performCipherOperation(Cipher.DECRYPT_MODE, iv, encryptKey, cipherText);
return ECKeyPair.create(privateKey);
}

注释的代码行为 web3j 中的内容 ,到了这里我们还需要导入相应的so库,我们在src/main下创建jniLibs,接着放入对应平台so

全部so笔者已上传到 Android scrypt so

现在调用的是修改后的方法 LWallet.decrypt(...)

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public Flowable<HLWallet> importKeystore(Context context, String keystore, String password) {
return Flowable.just(keystore)
.flatMap(s -> {
ObjectMapper objectMapper = new ObjectMapper();
WalletFile walletFile = objectMapper.readValue(keystore, WalletFile.class);
ECKeyPair keyPair = LWallet.decrypt(password, walletFile);
HLWallet hlWallet = new HLWallet(walletFile);

WalletFile generateWalletFile = Wallet.createLight(password, keyPair);
if (!generateWalletFile.getAddress().equalsIgnoreCase(walletFile.getAddress())) {
return Flowable.error(new HLError(ReplyCode.failure, new Throwable("address doesn't match private key")));
}

if (WalletManager.shared().isWalletExist(hlWallet.getAddress())) {
return Flowable.error(new HLError(ReplyCode.walletExisted, new Throwable("Wallet existed!")));
}
WalletManager.shared().saveWallet(context, hlWallet);
return Flowable.just(hlWallet);
});
}

Other FAQ

在开发中, 总是会有这样那样的疑问,这里做一个简单的答疑

Q. 怎么导出助记词啊 , imToken 有导出/备份助记词的功能 .

A. 很好的问题. 其实就是创建/用助记词解锁钱包时,app本地保存了助记词.导出只是将存储数据读取出来而已.可以尝试在imToken上通过导入Keystore或者私钥解锁钱包,就会发现没有备份助记词的入口.

Q. app本地需要保存钱包什么信息

A. 理论上说只需要保存钱包的Keystore.助记词,私钥最好别存,因为app一旦被破解,用户的钱包就能被直接获取到.如若有出于用户体验等原因保存这些敏感信息,最好结合用户输入的密码做对称加密保存.

以上即为以太坊解锁钱包的主要内容,过程中的坑基本有显式指明.

GitHub 系列教程代码已上传,如果对你有所帮助,请不吝点个star :)

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