加密md5算法

-(NSString *)md5:(NSString *)str {      const char *cStr = [str UTF8String];      unsigned char result[32];      CC_MD5( cStr, strlen(cStr), result );      return [NSString stringWithFormat:              @"XXXXXXXXXXXXXXXX",             result[0], result[1], result[2], result[3],              result[4], result[5], result[6], result[7],              result[8], result[9], result[10], result[11],              result[12], result[13], result[14], result[15]              ];  }