如何将十六进制公钥转换为用于Diffie-Hellman密钥交换的ASN.1 SubjectPublicKeyInfo结构？

Question

我正在尝试实现Diffie-Hellman密钥交换，以使用JAVA加密包生成用于加密/解密的对称密钥。这需要双方之间的公钥交换。

客户端共享的公钥是1024位十六进制字符串，应该用于计算共享密钥。如何将此字符串转换为编码的密钥格式（ASN.1 SubjectPublicKeyInfo结构）以创建PublicKey对象。

考虑示例公钥字符串。参数p和g被输入inputDHParameterSpec对象。

示例实现：AutoGen密钥对：

    KeyPairGenerator clientKpairGen = keyPairGenerator.getInstance("DiffieHellman");
    clientKpairGen.initialize(inputDHParameterSpec);
    KeyPair clientKpair = clientKpairGen.generateKeyPair();
    byte[] clientPubKeyEnc = clientKpair.getPublic().getEncoded();

    X509EncodedKeySpec testPubKeySpec = new X509EncodedKeySpec(clientPubKeyEnc);
    KeyFactory keyFactory = KeyFactory.getInstance("DiffieHellman");
    PublicKey clientPubKey = keyFactory.generatePublic(testPubKeySpec);

Hex PublicKey - 失败：

    String testPublicKey = "85f04dd00345642ad12b65bd1a7c38728bff0b8e281ddb6ac4f2739e82a02145daabf23d173c933913b1f844059710e9125591569de427eae1d269accbfa3305069deb7622d1da3ad9820d11bd24fdcce5381d2df99bda314394738dfcbe210eae247b1303e79297ff746cd919e189f6a5776e6ecc24c8900de0f38f159072de";
    X509EncodedKeySpec testPubKeySpec = new X509EncodedKeySpec(hexStringToByteArray(testPublicKey));
    KeyFactory keyFactory = KeyFactory.getInstance("DiffieHellman");
    PublicKey clientPubKey = keyFactory.generatePublic(testPubKeySpec);//Failing here

在第一个代码块中创建的byte []具有ASN.1编码格式的公钥，但hexStringToByteArray（testPublicKey）仅将十六进制转换为byte []。由于这个原因，在标记的行上得到以下错误。

Exception in thread "main" java.security.spec.InvalidKeySpecException: Inappropriate key specification
    at com.sun.crypto.provider.DHKeyFactory.engineGeneratePublic(DHKeyFactory.java:85)
    at java.security.KeyFactory.generatePublic(KeyFactory.java:334)
    at MWK_DHGen.main(MWK_DHGen.java:87)
Caused by: java.security.InvalidKeyException: Error parsing key encoding
    at com.sun.crypto.provider.DHPublicKey.<init>(DHPublicKey.java:178)
    at com.sun.crypto.provider.DHKeyFactory.engineGeneratePublic(DHKeyFactory.java:78)
    ... 2 more

有人可以帮助如何将此十六进制转换为所需的格式吗？还鼓励使用此十六进制字符串来获取密钥的不同实现。

Answer 1

如果您已经拥有域参数（p，g）并且只有公钥的整数值，则可以使用DHPublicKeySpec而不是X509EncodedKeySpec：

String testPublicKey = "85f04dd00345642ad12b65bd1a7c38728bff0b8e281ddb6ac4f2739e82a02145daabf23d173c933913b1f844059710e9125591569de427eae1d269accbfa3305069deb7622d1da3ad9820d11bd24fdcce5381d2df99bda314394738dfcbe210eae247b1303e79297ff746cd919e189f6a5776e6ecc24c8900de0f38f159072de";
BigInteger publicKeyInteger = new BigInteger(testPublicKey, 16);
KeyFactory keyFactory = KeyFactory.getInstance("DiffieHellman");
PublicKey clientPubKey = keyFactory.generatePublic(new DHPublicKeySpec(publicKeyInteger, g, p));