Android 4.3 KeyStore - 在尝试检索密钥时链== null

在这篇博客之后,我正在使用此代码KeyPair在Android KeyStore中创建和存储:

Context ctx = getApplicationContext();
Calendar notBefore = Calendar.getInstance();
Calendar notAfter = Calendar.getInstance();
notAfter.add(1, Calendar.YEAR);
KeyPairGeneratorSpec spec = new KeyPairGeneratorSpec.Builder(ctx).
setAlias(RSA_KEYS_ALIAS).setSubject(
  new X500Principal(String.format("CN=%s, OU=%s", 
    getApplicationName(), ctx.getPackageName()))).
setSerialNumber(BigInteger.ONE).
setStartDate(notBefore.getTime()).setEndDate(notAfter.getTime()).build();

KeyPairGenerator kpGenerator;
try {
    kpGenerator = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");

    kpGenerator.initialize(spec);
    kpGenerator.generateKeyPair();
} catch (Exception e) {
    showException(e);
}

当我尝试使用此代码从KeyStore检索公钥时,会抛出NullPointerException带有消息的a chain == null.

public RSAPublicKey getRSAPublicKey() {
    RSAPublicKey result = null;
    try {
        KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
        keyStore.load(null);
        KeyStore.PrivateKeyEntry keyEntry = 
            (KeyStore.PrivateKeyEntry) keyStore.getEntry(RSA_KEYS_ALIAS, null); // --< exception is thrown here
        result = (RSAPublicKey) keyEntry.getCertificate().getPublicKey();
    }
    } catch (Exception e) {
        showException(e);
    }
    return result;
}

检索私钥的代码也是如此.

更新:

我将我的代码与Google BasicAndroidKeyStore示例进行了比较.在该样本中生成,存储和检索密钥对的机制几乎与我实现的相同.我很困惑为什么这段代码在经过几个月的完美工作后已停止运作.

任何建议或提示将不胜感激.