将字符串转换为加密密钥，反之亦然

公用密钥可以使用X509EnpredKeySpec进行存储，而私钥则使用PKCS8EnpredKeySpec。例如这样：

public static PrivateKey loadPrivateKey(String key64) throws GeneralSecurityException {    byte[] clear = base64Depre(key64);    PKCS8EnpredKeySpec keySpec = new PKCS8EnpredKeySpec(clear);    KeyFactory fact = KeyFactory.getInstance("DSA");    PrivateKey priv = fact.generatePrivate(keySpec);    Arrays.fill(clear, (byte) 0);    return priv;}public static PublicKey loadPublicKey(String stored) throws GeneralSecurityException {    byte[] data = base64Depre(stored);    X509EnpredKeySpec spec = new X509EnpredKeySpec(data);    KeyFactory fact = KeyFactory.getInstance("DSA");    return fact.generatePublic(spec);}public static String savePrivateKey(PrivateKey priv) throws GeneralSecurityException {    KeyFactory fact = KeyFactory.getInstance("DSA");    PKCS8EnpredKeySpec spec = fact.getKeySpec(priv, PKCS8EnpredKeySpec.class);    byte[] packed = spec.getEnpred();    String key64 = base64Enpre(packed);    Arrays.fill(packed, (byte) 0);    return key64;}public static String savePublicKey(PublicKey publ) throws GeneralSecurityException {    KeyFactory fact = KeyFactory.getInstance("DSA");    X509EnpredKeySpec spec = fact.getKeySpec(publ, X509EnpredKeySpec.class);    return base64Enpre(spec.getEnpred());}public static void main(String[] args) throws Exception {    KeyPairGenerator gen = KeyPairGenerator.getInstance("DSA");    KeyPair pair = gen.generateKeyPair();    String pubKey = savePublicKey(pair.getPublic());    PublicKey pubSaved = loadPublicKey(pubKey);    System.out.println(pair.getPublic()+"n"+pubSaved);    String privKey = savePrivateKey(pair.getPrivate());    PrivateKey privSaved = loadPrivateKey(privKey);    System.out.println(pair.getPrivate()+"n"+privSaved);}