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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：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。
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分块隐藏ECB和CBC
ECB：直接分块加密
for(int i=0;iCBC：与上块密文异或后加密，需要向量width;i++) for(int j=0;j height;j++) grey->imageData[j*grey->width+i]=bitrev(grey->imageData[j*grey->width+i]); cvNamedWindow("ecb"); cvShowImage("ecb", grey);
for(int i=0;iwidth;i++) for(int j=0;j 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：
推荐一下PHP、IOS和Android都能使用的加密方法：