CryptUtil.java

package cn.scau.scautreasure.util;

import android.util.Base64;
import org.androidannotations.annotations.EBean;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

@EBean
public class CryptUtil {

	private String seed = "asdhkjhcvn9+5";
    private final static int JELLY_BEAN_4_2 = 17;

    public static String base64_url_safe(String var){
        return Base64.encodeToString(var.getBytes(), Base64.URL_SAFE | Base64.NO_WRAP);
    }

    public String encrypt(String cleartext) {
		try {

			byte[] rawKey = getRawKey(seed.getBytes());
			byte[] result;
			result = encrypt(rawKey, cleartext.getBytes());
			return toHex(result);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	public String decrypt(String encrypted) {
		try {

			byte[] rawKey;
			rawKey = getRawKey(seed.getBytes());

			byte[] enc = toByte(encrypted);
			byte[] result = decrypt(rawKey, enc);
			return new String(result);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}


	private byte[] getRawKey(byte[] seed) throws Exception {
		KeyGenerator kgen = KeyGenerator.getInstance("AES");
        SecureRandom sr = null;
        if (android.os.Build.VERSION.SDK_INT >=  JELLY_BEAN_4_2) {
            sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");
        } else {
            sr = SecureRandom.getInstance("SHA1PRNG");
        }
		sr.setSeed(seed);
		kgen.init(128, sr); // 192 and 256 bits may not be available
		SecretKey skey = kgen.generateKey();
		byte[] raw = skey.getEncoded();
		return raw;
	}

	private byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
		SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
		byte[] encrypted = cipher.doFinal(clear);
		return encrypted;
	}

	private byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
		SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.DECRYPT_MODE, skeySpec);
		byte[] decrypted = cipher.doFinal(encrypted);
		return decrypted;
	}

	public String toHex(String txt) {
		return toHex(txt.getBytes());
	}

	public String fromHex(String hex) {
		return new String(toByte(hex));
	}

	public byte[] toByte(String hexString) {
		int len = hexString.length() / 2;
		byte[] result = new byte[len];
		for (int i = 0; i < len; i++)
			result[i] = Integer.valueOf(hexString.substring(2 * i, 2 * i + 2),
					16).byteValue();
		return result;
	}

	public String toHex(byte[] buf) {
		if (buf == null)
			return "";
		StringBuffer result = new StringBuffer(2 * buf.length);
		for (int i = 0; i < buf.length; i++) {
			appendHex(result, buf[i]);
		}
		return result.toString();
	}

	private final String HEX = "0123456789ABCDEF";

	private void appendHex(StringBuffer sb, byte b) {
		sb.append(HEX.charAt((b >> 4) & 0x0f)).append(HEX.charAt(b & 0x0f));
	}

}