对于登陆注册的加密

关于各种加密方式的使用场景##

1.通过简单的URLENCODE ＋ BASE64编码防止数据明文传输
2.对普通请求、返回数据，生成MD5校验（MD5中加入动态密钥），进行数据完整性（简单防篡改，安全性较低，优点：快速）校验。
3.对于重要数据，使用RSA进行数字签名，起到防篡改作用。
4.对于比较敏感的数据，如用户信息（登陆、注册等），客户端发送使用RSA加密，服务器返回使用DES(AES)加密。
注：客户端发送之所以使用RSA加密，是因为RSA解密需要知道服务器私钥，而服务器私钥一般盗取难度较大；如果使用DES的话，可以通过破解客户端获取密钥，安全性较低。而服务器返回之所以使用DES，是因为不管使用DES还是RSA，密钥（或私钥）都存储在客户端，都存在被破解的风险，而RSA速度比较慢，所以使用DES。

1.DM5###

//因为是使用category，没有参数传入
-(NSString *) stringFromMD5 {
       if(self == nil || [self length] == 0) {
             return nil;
       }
       const char *value = [self UTF8String];
       unsigned char outputBuffer[CC_MD5_DIGEST_LENGTH];
       CC_MD5(value, strlen(value), outputBuffer);
       NSMutableString *outputString = [[NSMutableString alloc] initWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
       for(NSInteger count = 0; count < CC_MD5_DIGEST_LENGTH; count++){
              [outputString appendFormat:@"%02x",outputBuffer[count]];
       }
       return [outputString autorelease];
}

2.Base64###

+ (NSString *) base64EncodeData: (NSData *) objData {
     const unsigned char * objRawData = [objData bytes];
     char * objPointer;char * strResult;
     // Get the Raw Data length and ensure we actually have data
     int intLength = [objData length];
     if (intLength == 0) return nil;
     // Setup the String-based Result placeholder and pointer within that placeholder
     strResult = (char *)calloc(((intLength + 2) / 3) * 4, sizeof(char));
     objPointer = strResult;
     // Iterate through everything
     while (intLength > 2) { 
          // keep going until we have less than 24 bits*objPointer++ = _base64EncodingTable[objRawData[0] >> 2];
          *objPointer++ = _base64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)];
          *objPointer++ = _base64EncodingTable[((objRawData[1] & 0x0f) << 2) + (objRawData[2] >> 6)];
          *objPointer++ = _base64EncodingTable[objRawData[2] & 0x3f];
          // we just handled 3 octets (24 bits) of data
          objRawData += 3;
          intLength -= 3;
}
     // now deal with the tail end of things
     if (intLength != 0) {
           *objPointer++ = _base64EncodingTable[objRawData[0] >> 2];
           if (intLength > 1) {
                 *objPointer++ = _base64EncodingTable[((objRawData[0] & 0x03) << 4) + (objRawData[1] >> 4)];
                 *objPointer++ = _base64EncodingTable[(objRawData[1] & 0x0f) << 2];
                 *objPointer++ = '=';
            } 
            else {
                   *objPointer++ = _base64EncodingTable[(objRawData[0] & 0x03) << 4];
                   *objPointer++ = '=';
                   *objPointer++ = '=';
                   }
             }// Terminate the string-based result
             *objPointer = '\0';
             NSString *rstStr = [NSString stringWithCString:strResult encoding:NSASCIIStringEncoding];
             free(objPointer);
             return rstStr;
}

3.AES###

-(NSData*) EncryptAES: (NSString *) key {
     char keyPtr[kCCKeySizeAES256+1];
     bzero(keyPtr, sizeof(keyPtr));
     [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
     NSUInteger dataLength = [self length];
     size_t bufferSize = dataLength + kCCBlockSizeAES128;
     void *buffer = malloc(bufferSize);
     size_t numBytesEncrypted = 0;
     CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,kCCOptionPKCS7Padding | kCCOptionECBMode,keyPtr, kCCBlockSizeAES128,NULL,[self bytes], dataLength,buffer, bufferSize,&numBytesEncrypted);
     if (cryptStatus == kCCSuccess) {
            return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
     }
     free(buffer);
     return nil;
}

4.RSA###

- (NSData *) encryptWithData:(NSData *)content {
     size_t plainLen = [content length];if (plainLen > maxPlainLen) {
          NSLog(@"content(%ld) is too long, must < %ld", plainLen, maxPlainLen);
          return nil;
     }
     void *plain = malloc(plainLen);
     [content getBytes:plainlength:plainLen];
     size_t cipherLen = 128; // currently RSA key length is set to 128 bytes
     void *cipher = malloc(cipherLen);
     OSStatus returnCode = SecKeyEncrypt(publicKey, kSecPaddingPKCS1, plain,plainLen, cipher, &cipherLen);
     NSData *result = nil;
     if (returnCode != 0) {
          NSLog(@"SecKeyEncrypt fail. Error Code: %ld", returnCode);
     }
     else {
          result = [NSData dataWithBytes:cipherlength:cipherLen];
     }
     free(plain);
     free(cipher);
     return result;
}