Loading raw 64-byte long ECDSA public key in Java

Question

I have a raw (r,s) format ECDSA NIST P-256 public key. It seems that there is no simple way to load it into an object that implements java.security.interfaces.ECPublicKey.

Answer 1

The EC Public Key is a point that consists of x and y co-ordinate. I wrote the following code segment once to convert EC x, y point to publicKey object. Hope this will help you. For your information:

rawPubKey = 04 + x co-ordinate + y co-ordinate (Hex String)

curveName = P-256 (String)

Example EC Public Key Point for P-256:

rawPubKey = 04 6B17D1F2E12C4247F8BCE6E563A440F277037D812DEB33A0F4A13945D898C296 4FE342E2FE1A7F9B8EE7EB4A7C0F9E162BCE33576B315ECECBB6406837BF51F5

BC Provider: You need Bouncy Castle provider. I used bcprov-jdk15on-149.jar, but you can download the latest version from here.

/**
 * This method converts the uncompressed raw EC public key into java.security.interfaces.ECPublicKey
 * @param rawPubKey 
 * @param curveName
 * @return java.security.interfaces.ECPublicKey
 */
public ECPublicKey ucPublicKeyToPublicKey(String rawPubKey, String curveName) {
    byte[] rawPublicKey = Helper.toByte(rawPubKey); 
    ECPublicKey ecPublicKey = null;
    KeyFactory kf = null;
    
    ECNamedCurveParameterSpec ecNamedCurveParameterSpec = ECNamedCurveTable.getParameterSpec(curveName);
    ECCurve curve = ecNamedCurveParameterSpec.getCurve();
    EllipticCurve ellipticCurve = EC5Util.convertCurve(curve, ecNamedCurveParameterSpec.getSeed());
    java.security.spec.ECPoint ecPoint = ECPointUtil.decodePoint(ellipticCurve, rawPublicKey);
    ECParameterSpec ecParameterSpec = EC5Util.convertSpec(ellipticCurve, ecNamedCurveParameterSpec);
    java.security.spec.ECPublicKeySpec publicKeySpec = new java.security.spec.ECPublicKeySpec(ecPoint, ecParameterSpec);
    
    kf = java.security.KeyFactory.getInstance("EC");
    
    try {
        ecPublicKey = (ECPublicKey) kf.generatePublic(publicKeySpec);
    } catch (Exception e) {
        System.out.println("Caught Exception public key: " + e.toString());
    }
    
    return ecPublicKey;
}

EDIT: Here is toByte() method:

public static byte[] toByte(String hex) {
        if (hex == null)
            return null;
        hex = hex.replaceAll("\\s", "");
        byte[] buffer = null;
        if (hex.length() % 2 != 0) {
            hex = "0" + hex;
        }
        int len = hex.length() / 2;
        buffer = new byte[len];
        for (int i = 0; i < len; i++) {
            buffer[i] = (byte) Integer.parseInt(
                    hex.substring(i * 2, i * 2 + 2), 16);
        }
        return buffer;
    }

But you can use your own implementation. Here is another one:

import javax.xml.bind.DatatypeConverter;
public static byte[] toByte(String hex) {{
    return DatatypeConverter.parseHexBinary(hex);
}