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크리에이티브 커먼즈 라이선스
Creative Commons License
출처 : http://www.androidsnippets.com/encryptdecrypt-strings

Simple helper class to encrypt and decrypt strings using AES128. The result is Ascii-encoded (actually hex, no base64), so no byte[] has to be stored. A SEED value is used as a shared secret ("Master-Password"). Only with the same SEED the stored values can be decrypted.

package net.sf.andhsli.hotspotlogin;

import java.security.SecureRandom;

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

/**
 * Usage:
 * 
 * String crypto = SimpleCrypto.encrypt(masterpassword, cleartext)
 * ...
 * String cleartext = SimpleCrypto.decrypt(masterpassword, crypto)
 * </pre>
 * @author ferenc.hechler
 */
public class SimpleCrypto {

	public static String encrypt(String seed, String cleartext) throws Exception {
		byte[] rawKey = getRawKey(seed.getBytes());
		byte[] result = encrypt(rawKey, cleartext.getBytes());
		return toHex(result);
	}
	
	public static String decrypt(String seed, String encrypted) throws Exception {
		byte[] rawKey = getRawKey(seed.getBytes());
		byte[] enc = toByte(encrypted);
		byte[] result = decrypt(rawKey, enc);
		return new String(result);
	}

	private static byte[] getRawKey(byte[] seed) throws Exception {
		KeyGenerator kgen = KeyGenerator.getInstance("AES");
		SecureRandom 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 static 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 static 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 static String toHex(String txt) {
		return toHex(txt.getBytes());
	}
	public static String fromHex(String hex) {
		return new String(toByte(hex));
	}
	
	public static 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 static 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 static String HEX = "0123456789ABCDEF";
	private static void appendHex(StringBuffer sb, byte b) {
		sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
	}
	
}

// see http://androidsnippets.com/encryptdecrypt-strings


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