CODEWITHSUNDEEP
javakeystorepublic-key-encryption
Sajith Vijesekara
Sajith Vijesekara

Reputation: 1372

Generate ECPublicKey in java

I am new to java ecc encryption. So I got ECC public key data array from java card.the size is 49 byte length. So I need to generate Eccpublic key. So I have created public key. but it gives error:

java.security.spec.InvalidKeySpecException: encoded key spec not recognised

This is my code. How to generate Eccpublickey using data array?

byte[] pub = new byte[] {
    /*(Public data) 49 length byte ARRAY
    */


     };

    System.out.println("Length :" + pub.length);
    X509EncodedKeySpec ks = new X509EncodedKeySpec(pub);

    KeyFactory kf;
    try {
        kf = KeyFactory.getInstance("ECDH");

    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
        return;
    }

    ECPublicKey remotePublicKey;

    try {
        remotePublicKey = (ECPublicKey) kf.generatePublic(ks);
    } catch (InvalidKeySpecException e) {
        e.printStackTrace();
        return;
    } catch (ClassCastException e) {
        e.printStackTrace();
        return;
    }
    System.out.println(remotePublicKey);

} catch (Exception e) {
    e.printStackTrace();
}

Upvotes: 0

Views: 1657

Answers (2)

k_o_
k_o_

Reputation: 6288

The Java Card key is encoded in plain text form. I tried to use mostly plain Java, but the decoding process from the byte array representation requires still BouncyCastle's ECPointUtil. Maybe there is a built-in way to do this, but I have not come across one.

The format is simple: It starts with 04 and then the x, y coordinates are each on 32 bytes and can be used with a positive BigInteger when e.g. secp256r1 is used.

Example:

042b495a9b4142dc317624626ad108d4896c12a97af1a1372e9a7b0f29adcaeb49dee377c97fbb17b61480e857f5ce72408488e2763619159d032d3be091266dd6

BigInteger x = new BigInteger(1, pubKey, 1, 32)
BigInteger y = new BigInteger(1, pubKey, 32, 32)

The tricky part is the use of AlgorithmParameters which is simple but in general an unknown API.

ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec("secp256r1");
AlgorithmParameters algorithmParameters = AlgorithmParameters.getInstance("EC");
algorithmParameters.init(ecGenParameterSpec);
ECParameterSpec ecParameterSpec = algorithmParameters.getParameterSpec(ECParameterSpec.class);
ECPoint point = ECPointUtil.decodePoint(ecParameterSpec.getCurve(), pubKey);
KeyFactory keyFactory = KeyFactory.getInstance("EC");
ECPublicKeySpec ecPublicKeySpec = new ECPublicKeySpec(point, ecParameterSpec);
ECPublicKey ecPublicKey = (ECPublicKey) keyFactory.generatePublic(ecPublicKeySpec);

Upvotes: 1

Sajith Vijesekara
Sajith Vijesekara

Reputation: 1372

The reason is the code not working the keyspec can't use in ECC.so i found how to use ECPublicKeySpec in ECC.In here it has good explanation.https://bitcointalk.org/index.php?topic=2899.0;wap2 Thanks.

Upvotes: 0

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