title: How to initialize a EC key pair with an existing key pair in JavaCard?
body: <p>I already have a EC key pair(secp256r1) in a binary format which is stored in a byte array, like this:</p>
  
  <pre><code>// private key, 32 bytes
  byte[] privKey = {0x4c, (byte)0xc7, (byte)0xcf, 0x68, (byte)0x91, 0x18, (byte)0x96, (byte)0xc8, (byte)0xe2, (byte)0xf9, (byte)0xc8, (byte)0xcc, 0x2f, 0x7f, 0x0a, (byte)0xa2, 0x1c, 0x6a, (byte)0xcb, (byte)0xba, 0x38, 0x1c, 0x10, (byte)0x9a, (byte)0xfe, (byte)0x91, 0x18, (byte)0xf6, (byte)0xca, (byte)0xd9, 0x0f, 0x0b};
  //public key, 65 bytes, which is contained in a X.509 certificate
  byte[] pubKey = {0x04, 0x72, (byte)0x9a, 0x71, (byte)0xd0, (byte)0x81, 0x62, 0x42, (byte)0x84, (byte)0x92, (byte)0xf2, (byte)0xd9, 0x61, (byte)0x92, 0x4d, 0x37, 0x44, 0x3a, 0x4f, 0x1b, (byte)0xda, 0x58, 0x0f, (byte)0x8a, (byte)0xea, 0x29, 0x20, (byte)0xd2, (byte)0x99, 0x7c, (byte)0xbe, (byte)0xa4, 0x39, 0x60, (byte)0xce, 0x72, (byte)0x9e, 0x35, (byte)0xc1, (byte)0xf7, 0x40, (byte)0x92, (byte)0xf2, 0x25, 0x0e, 0x60, 0x74, (byte)0x82, 0x3f, (byte)0xc5, 0x7f, 0x33, 0x60, (byte)0xb7, (byte)0xcd, 0x39, 0x69, (byte)0xc3, (byte)0xc3, 0x12, 0x5e, (byte)0xce, 0x26, 0x5c, 0x29};
  </code></pre>
  
  <p>This EC key pair is generated by openssl. I want to store this EC key pair in my javacard applet, so that I can signature message with this EC private key every time.</p>
  
  <p>But I don't find any appropriate API in javacard 3 to set the EC key pair.</p>
  
  <p>I use this project <a href="https://github.com/Yubico/ykneo-curves/blob/master/applet/src/com/yubico/ykneo/curves/SecP256r1.java" rel="nofollow">https://github.com/Yubico/ykneo-curves/blob/master/applet/src/com/yubico/ykneo/curves/SecP256r1.java</a> to set the parameters in secp256r1.</p>
  
  <p><strong>UPDATE</strong><br>
  I do have set the parameters setW in ECPublicKey and setS in ECPrivateKey, and other parameters according to <a href="https://github.com/Yubico/ykneo-curves/blob/master/applet/src/com/yubico/ykneo/curves/SecP256r1.java" rel="nofollow">https://github.com/Yubico/ykneo-curves/blob/master/applet/src/com/yubico/ykneo/curves/SecP256r1.java</a>. Like this:</p>
  
  <pre><code>    privKey.setFieldFP(p, (short) 0, (short) p.length);
      privKey.setA(a, (short) 0, (short) a.length);
      privKey.setB(b, (short) 0, (short) b.length);
      privKey.setG(G, (short) 0, (short) G.length);
      privKey.setR(r, (short) 0, (short) r.length);
  
      byte[] privData = {(byte)0x25, (byte)0xc9, (byte)0xec, (byte)0xdc, (byte)0x4c, (byte)0x59, (byte)0xa3, (byte)0xe0, (byte)0x4f, (byte)0x01, (byte)0x56, (byte)0x97, (byte)0xf3, (byte)0xcb, (byte)0x60, (byte)0x5b, (byte)0x84, (byte)0x49, (byte)0x45, (byte)0x3a, (byte)0xe2, (byte)0x0e, (byte)0xd1, (byte)0xbd, (byte)0xc0, (byte)0xa7, (byte)0xe1, (byte)0xfa, (byte)0x82, (byte)0xee, (byte)0x3c, (byte)0x73};
      privKey.setS(privData, (short) 0, (short) privData.length);
  
      pubKey.setFieldFP(p, (short) 0, (short) p.length);
      pubKey.setA(a, (short) 0, (short) a.length);
      pubKey.setB(b, (short) 0, (short) b.length);
      pubKey.setG(G, (short) 0, (short) G.length);
      pubKey.setR(r, (short) 0, (short) r.length);
  
      byte[] pubData = {0x04, 0x00, (byte)0xb9, (byte)0x8f, (byte)0xcf, (byte)0xc3, (byte)0xc0, (byte)0xae, (byte)0x95, 0x6a, 0x5b, 0x12, 0x6d, (byte)0xbe, 0x43, (byte)0xe4, 0x7f, 0x09, 0x0d, (byte)0xde, 0x02, (byte)0xd2, 0x6b, 0x28, (byte)0x86, (byte)0xed, 0x2b, (byte)0xd7, (byte)0xe2, (byte)0xc2, 0x69, (byte)0xc1, (byte)0x89, (byte)0xb2, 0x53, (byte)0x96, (byte)0xc1, 0x2d, (byte)0xbf, 0x4c, 0x30, (byte)0xae, (byte)0xd5, (byte)0xd5, 0x3c, (byte)0xb5, (byte)0xf9, 0x3b, 0x20, 0x37, (byte)0x83, (byte)0x88, (byte)0x9f, 0x34, 0x74, (byte)0xf5, 0x6c, (byte)0x97, 0x1e, 0x0a, (byte)0xa9, (byte)0xe7, (byte)0xfa, (byte)0xa6, 0x69};
      pubKey.setW(pubData, (short) 0, (short)pubData.length);
  </code></pre>
  
  <p>Now I signature the message:</p>
  
  <pre><code>    // the class Secp256r1 can be found in above link
      pair = SecP256r1.newKeyPair();
  
      ECPublicKey pubKey = (ECPublicKey) pair.getPublic();
      ECPrivateKey privKey = (ECPrivateKey) pair.getPrivate();
  
  
      byte[] data = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};
  
  
      signature = Signature.getInstance(Signature.ALG_ECDSA_SHA, false);
      signature.init(pair.getPrivate(), Signature.MODE_SIGN);
  
      byte[] signData = new byte[127];
      short sendLen = signature.sign(data, (short) 0, (short) data.length, buffer, (short) 0);
      apdu.setOutgoingAndSend((short) 0, sendLen);
  </code></pre>
  
  <p>I send several APDUs to call this code fragment. But every time I receive a differnt sign message. Why should this happened?</p>