java.security.InvalidKeyException: invalid key format on generating RSA public key

Question

Background:

I have created an applet to extract public key of a certificate extracted from a smart card. This public key is then stored in database. The private key of certificate is used to sign data and the public key is then used to verify the signature. Code for extracting public key from certificate:

private byte[] getPublicKey(KeyStore paramKeyStore)
    throws GeneralSecurityException {
  Enumeration localEnumeration = paramKeyStore.aliases();

  if (localEnumeration.hasMoreElements()) {
    String element = (String) localEnumeration.nextElement();
    Certificate[] arrayOfCertificate =
        paramKeyStore.getCertificateChain(element);
    byte[] publicKeyByteArray =
        arrayOfCertificate[0].getPublicKey().getEncoded();

    return publicKeyByteArray;
  }
  throw new KeyStoreException("The keystore is empty!");
}

This publicKeyByteArray is then storeed in database as BLOB after converting to string using bytes2String method:

private static String bytes2String(byte[] bytes) {
  StringBuilder string = new StringBuilder();
  for (byte b : bytes) {
    String hexString = Integer.toHexString(0x00FF & b);
    string.append(hexString.length() == 1 ? "0" + hexString : hexString);
  }
  return string.toString();
}

The content of the BLOB(key) saved in database is:

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

After reading the stored public key byte[] from database, I try to convert it back to Public Key using following code:

Cipher rsa;
rsa = Cipher.getInstance("RSA");
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(pkey.getBytes());
PublicKey pk = keyFactory.generatePublic(publicKeySpec);
rsa.init(Cipher.DECRYPT_MODE, pk);
byte[] cipherDecrypt = rsa.doFinal(encryptedText.getBytes());

but it gives following error:

Caused by: java.security.InvalidKeyException: invalid key format
    at sun.security.x509.X509Key.decode(X509Key.java:387)
    at sun.security.x509.X509Key.decode(X509Key.java:403)
    at sun.security.rsa.RSAPublicKeyImpl.<init>(RSAPublicKeyImpl.java:83)
    at sun.security.rsa.RSAKeyFactory.generatePublic(RSAKeyFactory.java:298)
    at sun.security.rsa.RSAKeyFactory.engineGeneratePublic(RSAKeyFactory.java:201)

Please suggest the reason and resolution for this issue.

Answer 1

You must have an error in the way you read the key back from the database. The following code works just fine for me:

String key = "3082012230..."; // full key omitted for brevity
byte[] derPublicKey = DatatypeConverter.parseHexBinary(key);

KeyFactory keyFactory = KeyFactory.getInstance("RSA");
X509EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(derPublicKey);
keyFactory.generatePublic(publicKeySpec);

I would guess, based on the use of pkey.getBytes(), that you've simply tried to get the bytes from the string rather than hex-decoding it.