MD5加密方案

• 方案一：直接 MD5 (不够安全)
  pwd = pwd.md5String;
• 方案二: MD5 + key(key可以从服务器获得,仍然不够安全)
  pwd = [pwd stringByAppendingString:key].md5String;
• 方案三: 多次MD5

NSString *password = [str md5String];
password = [password md5String];

• 方案四 - 先MD5,后有规律的乱序

/**
 *  先加密, 后乱序
 */
- (NSString *)digest4:(NSString *)str{
    NSString * password = [str md5String];

    // 注册:  123 ----  2CB962AC59075B964B07152D234B7020
    // 登录:  123 ---   202CB962AC59075B964B07152D234B70

    NSString *header = [password substringToIndex:2];
    NSString *footer = [password substringFromIndex:2];

    password = [footer stringByAppendingString:header];

    return password;
}

终端命令:

# 得到文件的MD5值
$ md5 文件名

# 得到字符串的MD5值
md5 -s "string"