如何从EC公钥字节中获取PublicKey对象？

Question

我正在开发一个需要在(NIST P-256,P-256,prime256v1)公钥SHA256withECDSA的帮助下验证签名的应用程序secp256r1.

公钥在某个较早的时间点由不同的应用程序生成,并以十六进制编码存储在我的数据库中.这里十六进制字符串的格式等同于OpenSSL在调用先前生成openssl ec -in x.pem -noout -text的文件时将生成的十六进制字符串.消息和签名是从不同的应用程序接收的.请考虑以下测试数据:x.pemopenssl ecparam -genkey -name secp256r1 -out x.pem

// Stored in Database
byte[] pubKey = DatatypeConverter.parseHexBinary("049a55ad1e210cd113457ccd3465b930c9e7ade5e760ef64b63142dad43a308ed08e2d85632e8ff0322d3c7fda14409eafdc4c5b8ee0882fe885c92e3789c36a7a");

// Received from Other Application
byte[] message = DatatypeConverter.parseHexBinary("54686973206973206a75737420736f6d6520706f696e746c6573732064756d6d7920737472696e672e205468616e6b7320616e7977617920666f722074616b696e67207468652074696d6520746f206465636f6465206974203b2d29");
byte[] signature = DatatypeConverter.parseHexBinary("304402205fef461a4714a18a5ca6dce6d5ab8604f09f3899313a28ab430eb9860f8be9d602203c8d36446be85383af3f2e8630f40c4172543322b5e8973e03fff2309755e654");

现在这应该是一个有效的签名.

我的目标是使用Java和/或Bouncycastle加密API验证消息上的签名.我已经isValidSignature为此创建了一个方法:

private static boolean isValidSignature(byte[] pubKey, byte[] message,
        byte[] signature) throws NoSuchAlgorithmException, NoSuchProviderException, InvalidKeyException, SignatureException, InvalidKeySpecException {
    Signature ecdsaVerify = Signature.getInstance("SHA256withECDSA", new BouncyCastleProvider());
    ecdsaVerify.initVerify(getPublicKeyFromHex(pubKey));
    ecdsaVerify.update(message);
    return ecdsaVerify.verify(signature);
}

我试图提取公钥:

KeyFactory.generatePublic:

private static PublicKey getPublicKeyFromHex(byte[] pubKey) throws NoSuchAlgorithmException, NoSuchProviderException, InvalidKeySpecException {
    KeyFactory fact = KeyFactory.getInstance("ECDSA", new BouncyCastleProvider());
    return fact.generatePublic(new X509EncodedKeySpec(pubKey));
}

但这会抛出一个java.security.spec.InvalidKeySpecException(DER长度超过4个字节:26).我该怎么做才能解析这个？

Answer 1

椭圆曲线密钥对生成和关键工厂的Bouncy Castle示例代码让我非常接近.

一旦我设法创建了一个ECDSA密钥工厂和secp256r1/ NIST P-256/ P-256/ prime256v1曲线的曲线规范,我就可以用它ECPointUtil.decodePoint来获得一个曲线点.然后,我可以生成一个公钥规范,使我能够生成如下公钥:

private PublicKey getPublicKeyFromBytes(byte[] pubKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
    ECNamedCurveParameterSpec spec = ECNamedCurveTable.getParameterSpec("prime256v1");
    KeyFactory kf = KeyFactory.getInstance("ECDSA", new BouncyCastleProvider());
    ECNamedCurveSpec params = new ECNamedCurveSpec("prime256v1", spec.getCurve(), spec.getG(), spec.getN());
    ECPoint point =  ECPointUtil.decodePoint(params.getCurve(), pubKey);
    ECPublicKeySpec pubKeySpec = new ECPublicKeySpec(point, params);
    ECPublicKey pk = (ECPublicKey) kf.generatePublic(pubKeySpec);
    return pk;
}