Java科普之加密算法

本文来自http://blog.csdn.net/liuxian13183/ ，引用必须注明出处！

加密比较复杂，但今天公司有需求，就稍微再研究一下，方式只有两种，对称加密和非对称加密。对称加密是指加密后可以用原方法解密，如情报传输常用；非对称加密指加密后不可解密，有什么用途呢？登录的密码使用非对称加密，拿到加密后数据跟数据库存的数据对比，相同则让登录成功（也就说数据库不存明文密码，只存加密后的字符串），还有接口参数的校验等，例如md5参数校验；有了这种加密方式再不也担心用户名密码被盗了（除非密码本被盗等其他情况）。下面我们介绍几种常见的加密方法

通用的Base64

public class Base64 {

    static private final int BASELENGTH = 128;
    static private final int LOOKUPLENGTH = 64;
    static private final int TWENTYFOURBITGROUP = 24;
    static private final int EIGHTBIT = 8;
    static private final int SIXTEENBIT = 16;
    static private final int FOURBYTE = 4;
    static private final int SIGN = -128;
    static private final char PAD = '=';
    static private final boolean fDebug = false;
    static final private byte[] base64Alphabet = new byte[BASELENGTH];
    static final private char[] lookUpBase64Alphabet = new char[LOOKUPLENGTH];

    static {
        for (int i = 0; i < BASELENGTH; ++i) {
            base64Alphabet[i] = -1;
        }
        for (int i = 'Z'; i >= 'A'; i--) {
            base64Alphabet[i] = (byte) (i - 'A');
        }
        for (int i = 'z'; i >= 'a'; i--) {
            base64Alphabet[i] = (byte) (i - 'a' + 26);
        }

        for (int i = '9'; i >= '0'; i--) {
            base64Alphabet[i] = (byte) (i - '0' + 52);
        }

        base64Alphabet['+'] = 62;
        base64Alphabet['/'] = 63;

        for (int i = 0; i <= 25; i++) {
            lookUpBase64Alphabet[i] = (char) ('A' + i);
        }

        for (int i = 26, j = 0; i <= 51; i++, j++) {
            lookUpBase64Alphabet[i] = (char) ('a' + j);
        }

        for (int i = 52, j = 0; i <= 61; i++, j++) {
            lookUpBase64Alphabet[i] = (char) ('0' + j);
        }
        lookUpBase64Alphabet[62] = (char) '+';
        lookUpBase64Alphabet[63] = (char) '/';

    }

    private static boolean isWhiteSpace(char octect) {
        return (octect == 0x20 || octect == 0xd || octect == 0xa || octect == 0x9);
    }

    private static boolean isPad(char octect) {
        return (octect == PAD);
    }

    private static boolean isData(char octect) {
        return (octect < BASELENGTH && base64Alphabet[octect] != -1);
    }

    /**
     * Encodes hex octects into Base64
     *
     * @param binaryData Array containing binaryData
     * @return Encoded Base64 array
     */
    public static String encode(byte[] binaryData) {

        if (binaryData == null) {
            return null;
        }

        int lengthDataBits = binaryData.length * EIGHTBIT;
        if (lengthDataBits == 0) {
            return "";
        }

        int fewerThan24bits = lengthDataBits % TWENTYFOURBITGROUP;
        int numberTriplets = lengthDataBits / TWENTYFOURBITGROUP;
        int numberQuartet = fewerThan24bits != 0 ? numberTriplets + 1
                : numberTriplets;
        char encodedData[] = null;

        encodedData = new char[numberQuartet * 4];

        byte k = 0, l = 0, b1 = 0, b2 = 0, b3 = 0;

        int encodedIndex = 0;
        int dataIndex = 0;
        if (fDebug) {
            System.out.println("number of triplets = " + numberTriplets);
        }

        for (int i = 0; i < numberTriplets; i++) {
            b1 = binaryData[dataIndex++];
            b2 = binaryData[dataIndex++];
            b3 = binaryData[dataIndex++];

            if (fDebug) {
                System.out.println("b1= " + b1 + ", b2= " + b2 + ", b3= " + b3);
            }

            l = (byte) (b2 & 0x0f);
            k = (byte) (b1 & 0x03);

            byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2)
                    : (byte) ((b1) >> 2 ^ 0xc0);
            byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4)
                    : (byte) ((b2) >> 4 ^ 0xf0);
            byte val3 = ((b3 & SIGN) == 0) ? (byte) (b3 >> 6)
                    : (byte) ((b3) >> 6 ^ 0xfc);

            if (fDebug) {
                System.out.println("val2 = " + val2);
                System.out.println("k4   = " + (k << 4));
                System.out.println("vak  = " + (val2 | (k << 4)));
            }

            encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[(l << 2) | val3];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[b3 & 0x3f];
        }

        // form integral number of 6-bit groups
        if (fewerThan24bits == EIGHTBIT) {
            b1 = binaryData[dataIndex];
            k = (byte) (b1 & 0x03);
            if (fDebug) {
                System.out.println("b1=" + b1);
                System.out.println("b1<<2 = " + (b1 >> 2));
            }
            byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2)
                    : (byte) ((b1) >> 2 ^ 0xc0);
            encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[k << 4];
            encodedData[encodedIndex++] = PAD;
            encodedData[encodedIndex++] = PAD;
        } else if (fewerThan24bits == SIXTEENBIT) {
            b1 = binaryData[dataIndex];
            b2 = binaryData[dataIndex + 1];
            l = (byte) (b2 & 0x0f);
            k = (byte) (b1 & 0x03);

            byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2)
                    : (byte) ((b1) >> 2 ^ 0xc0);
            byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4)
                    : (byte) ((b2) >> 4 ^ 0xf0);

            encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];
            encodedData[encodedIndex++] = lookUpBase64Alphabet[l << 2];
            encodedData[encodedIndex++] = PAD;
        }

        return new String(encodedData);
    }

    /**
     * Decodes Base64 data into octects
     *
     * @param encoded string containing Base64 data
     * @return Array containind decoded data.
     */
    public static byte[] decode(String encoded) {

        if (encoded == null) {
            return null;
        }

        char[] base64Data = encoded.toCharArray();
        // remove white spaces
        int len = removeWhiteSpace(base64Data);

        if (len % FOURBYTE != 0) {
            return null;// should be divisible by four
        }

        int numberQuadruple = (len / FOURBYTE);

        if (numberQuadruple == 0) {
            return new byte[0];
        }

        byte decodedData[] = null;
        byte b1 = 0, b2 = 0, b3 = 0, b4 = 0;
        char d1 = 0, d2 = 0, d3 = 0, d4 = 0;

        int i = 0;
        int encodedIndex = 0;
        int dataIndex = 0;
        decodedData = new byte[(numberQuadruple) * 3];

        for (; i < numberQuadruple - 1; i++) {

            if (!isData((d1 = base64Data[dataIndex++]))
                    || !isData((d2 = base64Data[dataIndex++]))
                    || !isData((d3 = base64Data[dataIndex++]))
                    || !isData((d4 = base64Data[dataIndex++]))) {
                return null;
            }// if found "no data" just return null

            b1 = base64Alphabet[d1];
            b2 = base64Alphabet[d2];
            b3 = base64Alphabet[d3];
            b4 = base64Alphabet[d4];

            decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
            decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
            decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);
        }

        if (!isData((d1 = base64Data[dataIndex++]))
                || !isData((d2 = base64Data[dataIndex++]))) {
            return null;// if found "no data" just return null
        }

        b1 = base64Alphabet[d1];
        b2 = base64Alphabet[d2];

        d3 = base64Data[dataIndex++];
        d4 = base64Data[dataIndex++];
        if (!isData((d3)) || !isData((d4))) {// Check if they are PAD characters
            if (isPad(d3) && isPad(d4)) {
                if ((b2 & 0xf) != 0)// last 4 bits should be zero
                {
                    return null;
                }
                byte[] tmp = new byte[i * 3 + 1];
                System.arraycopy(decodedData, 0, tmp, 0, i * 3);
                tmp[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
                return tmp;
            } else if (!isPad(d3) && isPad(d4)) {
                b3 = base64Alphabet[d3];
                if ((b3 & 0x3) != 0)// last 2 bits should be zero
                {
                    return null;
                }
                byte[] tmp = new byte[i * 3 + 2];
                System.arraycopy(decodedData, 0, tmp, 0, i * 3);
                tmp[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
                tmp[encodedIndex] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
                return tmp;
            } else {
                return null;
            }
        } else { // No PAD e.g 3cQl
            b3 = base64Alphabet[d3];
            b4 = base64Alphabet[d4];
            decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
            decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
            decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);

        }

        return decodedData;
    }

    /**
     * remove WhiteSpace from MIME containing encoded Base64 data.
     *
     * @param data the byte array of base64 data (with WS)
     * @return the new length
     */
    private static int removeWhiteSpace(char[] data) {
        if (data == null) {
            return 0;
        }

        // count characters that's not whitespace
        int newSize = 0;
        int len = data.length;
        for (int i = 0; i < len; i++) {
            if (!isWhiteSpace(data[i])) {
                data[newSize++] = data[i];
            }
        }
        return newSize;
    }
}

Md5加密，主要用于C端对参数加密后做一个签名，然后S端采取同样操作，签名一致则认为安全，返回数据；目的，为了防止恶意添加参数，盗取数据；原理：非对称加密，加密过程单向不可逆，比较加密后的结果；应用方式，下面是通用的密码本，所以很容易破解，当然也可以自定义密码本（C/S一致即可）。

    // 全局数组
    private final static String[] strDigits = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f"};
    protected static char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};

    // 返回形式为数字跟字符串
    private static String byteToArrayString(byte bByte) {
        int iRet = bByte;
        // System.out.println("iRet="+iRet);
        if (iRet < 0) {
            iRet += 256;
        }
        int iD1 = iRet / 16;
        int iD2 = iRet % 16;
        return strDigits[iD1] + strDigits[iD2];
    }

    // 转换字节数组为16进制字串
    private static String byteToString(byte[] bByte) {
        StringBuffer sBuffer = new StringBuffer();
        for (int i = 0; i < bByte.length; i++) {
            sBuffer.append(byteToArrayString(bByte[i]));
        }
        return sBuffer.toString();
    }

    public static String MD5Encrypt(String strObj) {
        String resultString = null;
        try {
            resultString = new String(strObj);
            MessageDigest md = MessageDigest.getInstance("MD5");
            // md.digest() 该函数返回值为存放哈希值结果的byte数组
            resultString = byteToString(md.digest(strObj.getBytes()));
        } catch (NoSuchAlgorithmException ex) {
            ex.printStackTrace();
        }
        return resultString;
    }

Des加密-（Data Encryption Standard），由56位密钥和8位奇偶检验符组成，通过异或、移位、置换和代换四种操作循环完成，如果一台PC计算能力是一秒一百万次，那么需要2000年才能破解，破解的方案只有穷举法猜出它的密码本或者暴力方式。特别说明一点，使用DES加密的KEY只有前8位有效，写多了也是多余。对称加密，加密方式可逆，用于双方各持有的一个密码本，一个加密一个解密，二战期间的情报加密方式类似这种。

private static String encoding = "UTF-8";

	/**
	 * sKey 奇偶校验位  加密字符串
	 */
	public static String encrypTo(String sKey, String str) {
		String result = str;
		if (str != null && str.length() > 0) {
			try {
				byte[] encodeByte = str.getBytes(encoding);
				byte[] encoder = getSymmetricResult(Cipher.ENCRYPT_MODE, sKey, encodeByte);
				result = Base64.encode(encoder).toString();
			} catch (Exception e) {
				e.printStackTrace();
				return "";
			}
		}
		return result;
	}

	/**
	 * sKey 奇偶校验位
	 * 解密字符串
	 */
	public static String decrypTo(String sKey, String str) {
		String result = str;
		if (str != null && str.length() > 0) {
			try {
				byte[] decodeByte = Base64.decode(str);
				byte[] decoder = getSymmetricResult(Cipher.DECRYPT_MODE, sKey, decodeByte);
				result = new String(decoder, encoding);
			} catch (Exception e) {
				e.printStackTrace();
				return "";
			}
		}
		return result;
	}

	/**
	 * 对称加密字节数组并返回
	 *
	 * @param byteSource
	 *            需要加密的数据
	 * @return 经过加密的数据
	 * @throws Exception
	 */
	public static byte[] getSymmetricResult(int mode, String sKey, byte[] byteSource) throws Exception {
		try {
			SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
			byte[] keyData = sKey.getBytes();
			DESKeySpec keySpec = new DESKeySpec(keyData);
			Key key = keyFactory.generateSecret(keySpec);
			Cipher cipher = Cipher.getInstance("DES");
			cipher.init(mode, key);
			byte[] result = cipher.doFinal(byteSource);
			return result;
		} catch (Exception e) {
			throw e;
		} finally {
		}
	}

AES加密（Advanced Encryption Start）-DES的升级版本，密钥长度可能是128位、192位和256位中的一种，使用更为复杂的算法，对称加密，同样也是可逆的，但由于复杂度加大解密时间更长。

	/**
	 * 加密
	 *
	 * @param content
	 *            需要加密的内容
	 * @param password
	 *            加密密码
	 * @return
	 */
	public static byte[] encrypt(String password, String content) {
		try {
			KeyGenerator kgen = KeyGenerator.getInstance("AES");
			kgen.init(128, new SecureRandom(password.getBytes()));
			SecretKey secretKey = kgen.generateKey();
			byte[] enCodeFormat = secretKey.getEncoded();
			SecretKeySpec key = new SecretKeySpec(enCodeFormat, "AES");
			Cipher cipher = Cipher.getInstance("AES");// 创建密码器
			byte[] byteContent = content.getBytes("utf-8");
			cipher.init(Cipher.ENCRYPT_MODE, key);// 初始化
			byte[] result = cipher.doFinal(byteContent);
			return result; // 加密
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		} catch (NoSuchPaddingException e) {
			e.printStackTrace();
		} catch (InvalidKeyException e) {
			e.printStackTrace();
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		} catch (IllegalBlockSizeException e) {
			e.printStackTrace();
		} catch (BadPaddingException e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * 解密
	 *
	 * @param content
	 *            待解密内容
	 * @param password
	 *            解密密钥
	 * @return
	 */
	public static byte[] decrypt(String password, byte[] content) {
		try {
			KeyGenerator kgen = KeyGenerator.getInstance("AES");
			kgen.init(128, new SecureRandom(password.getBytes()));
			SecretKey secretKey = kgen.generateKey();
			byte[] enCodeFormat = secretKey.getEncoded();
			SecretKeySpec key = new SecretKeySpec(enCodeFormat, "AES");
			Cipher cipher = Cipher.getInstance("AES");// 创建密码器
			cipher.init(Cipher.DECRYPT_MODE, key);// 初始化
			byte[] result = cipher.doFinal(content);
			return result; // 加密
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		} catch (NoSuchPaddingException e) {
			e.printStackTrace();
		} catch (InvalidKeyException e) {
			e.printStackTrace();
		} catch (IllegalBlockSizeException e) {
			e.printStackTrace();
		} catch (BadPaddingException e) {
			e.printStackTrace();
		}
		return null;
	}

	public static void main(String[] args) {
		String sKey = "adsasafq";
		String str = "Hello World";
		byte[] aesEncryptStr = AESEncrypt.encrypt(sKey, str);
		byte[] aesDecryptStr = AESEncrypt.decrypt(sKey, aesEncryptStr);
		System.out.println(new String(aesDecryptStr));
	}

Sha加密-（Secure Hash Algorithm），与MD5算法类似，但复杂度要高出32个量级，不对称加密，加密过程不可逆，其中SHA-1-224-256-384-512加密复杂度依次增加，

	/**
	 * 散列算法
	 *
	 * @param byteSource
	 *            需要散列计算的数据
	 * @return 经过散列计算的数据
	 * @throws Exception
	 */
	public static String getShaStr(byte[] byteSource) {
		try {
			MessageDigest currentAlgorithm = MessageDigest.getInstance("SHA-256");
			currentAlgorithm.reset();
			currentAlgorithm.update(byteSource);
			return bytes2String(currentAlgorithm.digest());
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	private static String bytes2String(byte[] aa) {// 将字节数组转换为字符串
		String hash = "";
		for (int i = 0; i < aa.length; i++) {// 循环数组
			int temp;
			if (aa[i] < 0) // 判断是否是负数
				temp = 256 + aa[i];
			else
				temp = aa[i];
			if (temp < 16)
				hash += "0";
			hash += Integer.toString(temp, 16);// 转换为16进
		}
		hash = hash.toUpperCase(); // 转换为大写
		return hash;
	}

	public static void main(String[] args) {
		String str = "Hello World";
		String shaEncryptStr = ShaEncrypt.getShaStr(str.getBytes());
		System.out.println(shaEncryptStr);// sha1-0A4D55A8D778E5022FAB701977C5D840BBC486D0
		System.out.println(shaEncryptStr.length());
	}

RSA加密（三位发明者名字首字母），由一个公钥和一个私钥组成，支付宝目前就采用这种加密方式，C端持有公钥，S端持有私钥，C端发送的加密数据只能由S端来处理，安全系统业界称为最高；原理是对两大素数的乘积做拆分，有无数种可能，所以只要公钥和私钥不泄密，一般就没有问题。非对称加密，但加密过程可逆。

根证书主要从VeriSign和GlobalSign两种，就是说默认得信任，否则就互联网没有信任基础了。

详见：欢迎大家提问Android技术及职业生涯等问题第9条

先简单介绍这几种，DES、AES对称加密，MD5、SHA（前两种又属于Hash算法）和RSA非对称加密。

有兴趣下载源码的请点击，源码！

分块隐藏ECB和CBC

ECB：直接分块加密

for(int i=0;i<grey->width;i++)
    for(int j=0;j<grey->height;j++)
        grey->imageData[j*grey->width+i]=bitrev(grey->imageData[j*grey->width+i]);
cvNamedWindow("ecb");
cvShowImage("ecb", grey);  

CBC：与上块密文异或后加密，需要向量

for(int i=0;i<grey->width;i++)
    for(int j=0;j<grey->height;j++)
        if(i!=0&&j!=0)
            grey->imageData[j*grey->width+i]=bitrev(grey->imageData[j*grey->width+i]^grey->imageData[j*grey->width+i-1]);
        else
            grey->imageData[0]=grey->imageData[0]^IV;
cvNamedWindow("cbc");
cvShowImage("cbc", grey); 

了解更多：http://snowolf.iteye.com/blog/379860

推荐一下PHP、IOS和Android都能使用的加密方法：http://www.funboxpower.com/php_android_ios_aes