Abstract:
The invention relates to a method for providing a computerized system which is protected from malicious programs coming from an external source, the method comprises the steps of (a) secretly, and in a manner unknown to authors of external programs, modifying one or more essential elements at the protected system in a manner which causes all running programs to fail, unless they are subjected to a compatible modification which enables them to run properly; and (b) modifying each program at the computerized system which is known to be benign in order to comply with said modification of one or more essential elements, thereby to enable it to be executed properly.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of information security. More particularly, the invention provides a system and method for protecting a computerized system from malicious code. More specifically, the invention modifies essential elements within the programing interface of the operating system or the instruction set for preventing the expected operation of any unauthorized code including malicious software. Any code which is expected to run on the operating system must be appropriately modified, otherwise, it will fail or will cause an alarm. 
     BACKGROUND OF THE INVENTION 
     The present art provides several manners by which a computerized system (including mobile devices, such as smart phones) can be protected from a malicious code:
         a. Preventing unauthorized code (hereinafter, also referred to as “program” or “application”) from entering the system, by checking its validity (such as its signature, its originating source, etc.);   b. Performing a static analysis of the program to ensure that it does not include a malicious code;   c. Shielding the operating system from being exploited through known vulnerabilities by constantly patching such vulnerabilities as soon as they are exposed.   d. Monitoring the behavior of suspicious programs while they run on the system or on a sandbox.       

     However, the abovementioned prior art means for the system protection suffer from at least one of the following flaws:
         a. They require a prior knowledge by the protector either with respect to the code, to its origin, or to its behavior;   b. They require assumptions with respect to normal or anomalous behavior of the protected system.   c. They require prior knowledge of exploitable vulnerabilities, and will not identify a new (hitherto unknown) exploit.   d. They may detect the malicious behavior too late, after a significant damage has already been caused to the system including the protected resources.   e. It is not clear when and how the malicious activity is triggered, furthermore, modern malware use evasion and anti-forensics techniques which severely hinder their detection.   f. A previously certified program may at some stage open the gate for malicious code.   g. Malicious code may operate solely in memory without passing through the file system.       

     The present invention is particularly, but not exclusively, applicable to any operating system whose source code is available for recompilation (Open Source); The concepts of the present invention can also be applied to binary code (Closed Source). Moreover, the present invention is particularly but not exclusively applicable to ‘isolated’ operating systems which are intended to run special purpose programs and are not designated to run a variety of third-party consumer applications; Yet the concepts of the present invention can be applied to other kinds of operating systems including operating systems for mobile devices. 
     Over the last few years, there have been reports of highly protected operating systems (OS), even isolated ones, that were compromised by malicious programs. Unlike a regular consumer-oriented OS, an isolated OS is designated to run special purpose programs. Malicious exploitation of such operating systems may bear critical consequences. At the same time new kinds of operating system such as Android were also being compromised at an accelerating rate. 
     Open source operating systems (primarily Linux) are widely being adopted in a wide range of domains, from smart phones to High Performance Computing (HPC). The open source operating systems may also be used in isolated systems. It is therefore an object of the present invention to provide a method and system for protecting a computerized system from malicious code, either known or unknown, either on open source systems or on closed source systems. 
     It is an object of the present invention to provide a method and system for protecting a computerized system from malicious code, which overcomes all the above mentioned drawbacks of existing means for detection and prevention. 
     It is another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which does not require any prior knowledge about the malicious program, its structure, its behavior, or its origin. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which does not require any assumption with respect to the normal or anomalous behavior of the protected system. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which does not require prior knowledge of exploitable vulnerabilities. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which can prevent any operation of an unauthorized program, or to route it to operate in a restricted supervised mode. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which is immune to common evasion and anti-forensics techniques. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code which bypasses the standard gate keeping mechanisms of a protected system. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code which operates solely in memory without passing through the file system. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which may either replace conventional protection means, or may cooperate with them. 
     It is still another object of the present invention to provide a method and system for protecting a computerized system from malicious code, which may be easily updated on a periodical basis, and may include random ingredients to thwart a bypass by the attacker. 
     Other objects and advantages of the present invention will become clear as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The invention relates to a method for providing a computerized system which is protected from malicious programs coming from an external source, the method comprises the steps of: (a) secretly, and in a manner unknown to authors of external programs, modifying one or more essential elements at the protected system in a manner which causes all running programs to fail, unless they are subjected to a compatible modification which enables them to run properly; and (b) modifying each program at the computerized system which is known to be benign in order to comply with said modification of one or more essential elements, thereby to enable it to be executed properly. 
     Preferably, said modifications involve a modification to one or more essential elements at the operating system, and to each benign program. 
     Preferably, when a program that does not comply with said modifications is found, the program is halted or sent to a sandbox, and an alert is raised. 
     Preferably, said modifications involve a modification to an operating system at said system, and wherein said modification to each benign program involves a compatible modification to the instruction set used by the program. 
     Preferably, said modifications involve a modification to an instruction set of a processor at said system, and wherein said modification to each benign program involves a compatible modification to the instruction set used by the program. 
     Preferably, the method of the invention is adapted for a static linking, wherein said modification at the protected system involves modification to at least one service routine and to a wrapper routine in the standard library, and wherein said modification to each of the benign programs is a compatible modification to the signature of the program. 
     Preferably, the method of the invention is adapted for a dynamic linking, wherein said modification at the protected system involves maintaining two copies of the dynamic standard library, a first copy of the dynamic standard library under its original name, and a under a modified name, and wherein said modification to each of the benign programs is a compatible modification to call said modified copy of the dynamic standard library. 
     Preferably, the method further includes a stub to detect programs that do not comply with said modification at the protected system. 
     Preferably, the method is adapted for a dynamic linking, wherein said modification at the protected system involves modification to a wrapper routine in the user mode and to the system call service routing in the kernel mode, and wherein said modification to each of the benign programs is a compatible modification to signatures of one or more system call invocations. 
     Preferably, said modification at the protected system involves modification to the names of one or more methods in a dynamic link library, and wherein each of the benign programs are modified to conform with said modification in said dynamic link library. 
     Preferably, the processor is a physical processor. Alternatively, the processor is a virtual processor. 
     Preferably, said modifications are made on a temporal basis, each time a different subset of essential elements and respective parameters are selected for modification. 
     Preferably, the modification to said program further involves recompilation and or relinking of the program. 
     Preferably, the modification to said operating system further involves recompilation and or relinking of the operating system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  shows in conceptual terms the manner by which protection of a conventional system is performed; 
         FIG. 2  shows in conceptual terms the manner by which protection of a computerized system according to the present invention is performed; 
         FIG. 3 a    illustrates a typical flow of a system call from its invocation at a user mode application, to its final implementation by a kernel mode service routing, in a conventional system, such as Linux; 
         FIG. 3 b    illustrates a first alternative of the first embodiment of the invention; 
         FIG. 3 c    illustrates a second alternative of the first embodiment adapted for handling dynamic linking; 
         FIG. 3 d    illustrates a third alternative of the first embodiment which is adapted to cope with dynamic linking without keeping two copies of the dynamic standard library as required by said second alternative; 
         FIG. 4 a    describes the typical manner by which an application accesses a dynamic library; 
         FIG. 4 b    describes the second embodiment of the present invention; 
         FIG. 5 a    shows the typical manner by which an application accesses a utility DLL; 
         FIG. 5 b    depicts the modifications made according to the third embodiment; 
         FIG. 6  depicts a fourth embodiment of the present invention, where modifications are made at the level of the instruction set; 
         FIG. 7 a    depicts a first alternative of a fifth embodiment of the present invention, where modifications are made to a virtual machine; and 
         FIG. 7 b    depicts a fifth embodiment of the present invention, where modifications are made to a Just in Time (JIT) compiler. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As noted above, prior art means for protecting a computerized system from a malicious program suffer from various kinds of drawbacks. As will be shown, the present invention overcomes all said drawbacks. 
     Modern operating systems, whether Open Source or Close Source, are designed with modularity and extensibility as primary guidelines. Standardization of the programing interface is therefore an essential requirement of all operating systems. 
     Some essential elements of the operating system are not expected to be modified, and when such elements are modified, some aspects of said element are traditionally expected to be kept untouched. For example, the set of system calls which are implemented by the operating system can be extended by the addition of a new system call, and the underlying code of an existing system call can be modified to enhance its performance. Yet the signature of an existing system call is traditionally expected to be kept untouched. Said signature includes the number and the types of the arguments (parameters) which are passed to the system call upon invocation, as well as the type of the ‘return value’ which is returned to the caller when the system call exits. 
     The very nature of modern operating systems prohibits such modifications because they compromise the need for a standard programming interface, which allows convenient development of useful programs, including applications as well as extensions to the operating system itself. Keeping the standard programming interface untouched, with the convenience which is guaranteed by this practice, is a highly attractive feature of any modern operating system. 
     Thus, deviations from the standard programming interface of a given operating system are regularly prohibited, and a developer of a new or existing program has no reason to anticipate any of such modifications. Furthermore, when such modifications (nonstandard deviations from the standard programming interface) occur, a developer of a new or existing program must have direct access to the modified programming interface, including the modified standard libraries. 
     It has been found by the inventors of this application, that the negative effects of said deviations can form an asset when coping with malicious programs. The present invention utilizes such unconventional modifications to the operating system to detect and prevent the operation of malicious programs, where the malware&#39;s author does not have access to the OS modifications. On the other hand, useful benign applications are properly modified by a central security authority to comply with the modified operating system, thus allowing them to run properly. 
     The present invention is particularly but not exclusively suited for Android devices. Android&#39;s kernel is open source Linux, and its user level applications run on the Dalvik virtual machine, which is also open source. An application which is intended to run on Dalvik is compiled into Dalvik bytecode, which is considerably easier to manipulate than hardware&#39;s machine code. Thus, even when a Dalvik application&#39;s source code is not provided, the application&#39;s bytecode can still be analyzed, manipulated, and/or decompiled in a relatively convenient and safe manner. 
     The following description provides five exemplary embodiments. Even though the concepts of the various embodiments are applicable to various types of operating systems and for various levels of code, for the sake of convenience and more clarity the following first and second embodiments are described in terms of the Linux operating system, while the third embodiment is described in terms of the Windows operating system, and the fourth embodiment is described in terms of the instruction-set at the machine level. The fifth embodiment is described in terms of Java or similar bytecode, where either a Virtual Machine (VM) or a Just In Time (JIT) compiler is applied. Furthermore, the invention as described herein is not limited to any particular level of the computerized system. For example, the modifications may be applied to essential elements of the operating system&#39;s user or kernel mode, to a hypervisor, or to the instruction set of the machine, either physical or virtual. 
       FIG. 1  shows in conceptual terms the manner by which protection of a conventional system is performed. Initially, a standard operating system is installed  110  and run  111 . When an external program  113  is encountered, the operating system routes the external program (through the so called “valid route”  150 ) to a “checking program” stage or module  120 . The term “external program”, refers herein to any new piece of code which originates outside of the running operating system. The “checking program” stage  120  checks in some conventional manner known in the art said external program to determine whether it is a malicious or a benign code. The “check program” stage  120  may also use a reputation knowledge base as a sort of “white list”. If the program is found to be benign, the operating system may load the program into memory in executable mode (step  122 ), and allows it to run (step  123 ). The check program stage  120 , may also monitor the external program while it runs, also in a conventional manner well known in the art. However, if the checking program stage  120  finds the external program to be malicious, the running of the program is aborted in step  121 , and additional measures well known in the art may also be taken. 
     As noted, the conventional protection manner of  FIG. 1  entirely depends on the “checking program” stage  120 , as any bypass of this stage will allow a malicious program to run on the system. More specifically, when the external program  113  somehow succeeds in taking the “invalid rout”  160 , it bypasses or evades the “checking program” stage  120 , and it can successfully run on the system, with all the damaging consequences associated with such evasion. In general terms, there are various manners (which involve either software or physical measures) by which a program may take the “invalid route”  160 . The defending side continuously tries to force an external program to use only the valid route  150 , while blocking possibilities to exploit the bypass route  160 . On the other hand, attackers continuously and repeatedly try to find ways to bypass or evade the valid route  150  (therefore avoid or mislead the “check program”  120 ), while using the bypass route  160 . When succeeding in taking the invalid route  160 , the malicious program can be loaded  122 , and run  123 , with all the damaging consequences. 
       FIG. 2  shows in conceptual terms the manner by which protection of a computerized system according to the present invention is performed. Initially, a standard operating system is internally modified  210  in a manner which is unknown to authors of external programs, either benign or malicious. As will be described hereinafter, various manners of modifications may be applied at this stage  210 . This modification to the operating system is generally intended to form a variant of the operating system which does not allow any external program to run on the modified operating system, unless this external program is subjected to a proper corresponding modification which cannot be foreseen by the external program author. In step  211 , the modified variant of the operating system is installed and run  212 . It should be noted that both steps  210  and  211  are performed by a central security authority  270 , which will be further discussed hereinafter. 
     Any external program  213  which is received at the central security authority  270  through a valid route  250 , is subjected to a validation procedure  221 . The validation procedure  221  thoroughly verifies that the program is benign. If the external program  220  is found to be malicious or otherwise suspicious, it is dropped  222 . Only if the external program  220  is found to be benign, it is subjected to a modification procedure  223 . The modification procedure  223  is intended to make the external program be compliant with the operating system as modified in step  210 . 
     Following said validation  221  and modification  223  of the external program  213 , the central security authority  270  installs  224  the external program as modified in step  223  on said modified operating system. In step  230 , the modified external program can be loaded into memory in an executable mode, and run in step  232 . 
     Any external program  213  which uses the invalid route  260  by bypassing or evading the central authority  270 , and arrives at the “load program” step  230 , will fail to run as depicted in step  231 , as it was not previously modified to comply with the modified operating system (as modified in step  210 ). This is in contrast to the prior art system of  FIG. 1 , in which any external program which succeeds in taking the invalid route  160  will be successfully loaded  122  and run  123 . 
     Some types of central security authority are known in previous art. One of the tasks of such prior art central security authorities is to validate external programs (i.e., programs from external origin). However, none of said central authorities perform the modification step  223  to comply with the operating system, as modified in step  210  (which is also performed by the central security authority  270 . 
     As previously noted, essential elements within the operating system are modified such that malicious programs that were originally compiled and linked with the original standard OS libraries, will not operate within the modified operating system. Any attempt at running them within the modified operating system will raise an alert to the central security authority, and subsequently may be either terminated or sandboxed. On the other hand, properly modified external programs will properly be loaded and run. 
     In a first embodiment of the invention, said modification is made to the signatures for a given subset of the operating system (OS), i.e., “system calls”. 
       FIG. 3 a    illustrates a typical flow of a system call from its invocation  1101   a  at a user mode application, to its final implementation by a kernel mode service routing  1202   a , in a conventional system, such as Linux. An application running at user mode  1100   a  initiates a system call invocation  1101   a , passing the call in a form of the standard signature of this specific system call, to a wrapper routine  1102   a  which resides in a standard library such as LIBC or its equivalent. In this context which is well known, the term signature typically refers to a function name, the types, order, and number of its parameters, and the type of the function&#39;s return value. The wrapper routine  1102   a  (also known as library routine) may perform some additional operations, and then it passes the call to the system call handler  1201   a  at kernel mode  1200   a . If the signature of the invoked function does match the signature expected by the wrapper routing  1102   a , then the call will fail with unexpected results. In case of static linking, the code will fail to link or even to compile. The system call handler  1201   a , residing at kernel mode  1200   a  receives the call from the wrapper routing  1102   a , and dispatches it to the proper system call service routine  1202   a , also in kernel mode. Here again, if the signature of the call passed from the handler  1201   a  does not match the expected signature, then the service routine  1202   a  will fail with unexpected consequences. Otherwise, in a normal operation when there is no exception, the service routine  1202   a  performs its assigned task, and returns the requested result along with a code which indicates success. As shown, a wrong signature will cause failure of the operation either at the standard library wrapper routine  1102   a  (at user mode  1100   a ) or at the service routine  1202   a  (at kernel mode). 
       FIG. 3 b    illustrates a first alternative of the first embodiment of the invention. In this alternative, the signature of at least one service routine  1202   b  is intentionally modified. Furthermore, the standard library wrapper routine  1102   b  is also intentionally modified to conform to said modified service routine  1202   b , while preserving the application call invocation  1101   b . This is particularly applicable to the case of static linking of the application&#39;s code with the standard library. More specifically, the wrapper routine  1102   b  is modified such that when it is called by the invocation  1101   b  with an original signature, it transforms the call into the signature expected by the modified service routine  1202   b . The service routine  1202   b  is modified such that it verifies that the received signature conforms to the modified form. In the affirmative case, the service routine  1202   b  proceeds normally. Otherwise, the service routine  1202   b  issues an alert which is followed by either terminating the caller application (which initiated the system call), or by letting the caller application to proceed under strict supervision. Clearly, the author of a malicious application will not be aware of said modifications, and therefore the malicious application will not be linked with the modified standard library, and will therefore fail upon calling the modified system call. Even if somehow the author of the malicious application will know that a modification was made, he does not have access to the crucial details of the modifications, and therefore his malicious application will fail. 
     As said, this first alternative of the first embodiment is particularly suited to static linking. However, there are many applications that use dynamic linking. In such case of dynamic linking, the standard library&#39;s wrapper routine  1102   b  will be called at runtime dynamically by any application which uses dynamic linking (whether it is malicious or benign), and said wrapper routine  1102   b  will transform the signature of the calling routine, resulting in the modified system call service routine  1202   b  being called and operate properly without raising any alert. 
       FIG. 3 c    illustrates a second alternative  3100  of the first embodiment adapted for handling dynamic linking. In said second alternative, the system keeps two different copies of the dynamic standard library as follows: (a) the original dynamic standard library (such as LIBC)  3202  is kept under its original name unmodified, while (b) a modified copy of the dynamic standard library  3102  (where the signatures are modified as noted above) is also kept under a different name. In addition, benign applications  3101  are modified to call said modified copy  3102  of the dynamic standard library (under its new name) rather than calling the original dynamic standard library  3202  (as note, for example, LIBC). However, in this second alternative the signature of the invocation is not modified within the application  3101 . In such an arrangement  3100 , at runtime any application  3201  which uses dynamic linking but is not modified to call the modified copy by its new name, will fail. Said failure will occur because the application will call the original, unmodified copy of the dynamic standard library  3202 , resulting in submitting a wrong signature to the modified kernel  3203 . 
     A third alternative  3200  of the first embodiment which is adapted to cope with dynamic linking without keeping two copies of the dynamic standard library as required by said second alternative, is illustrated in  FIG. 3 d   . The essential difference relative to said first and second alternatives is that the application itself is modified to contain the system call invocation  1101   d  with a modified signature, which in turn complies with the modified wrapper routine  1102   d  and with the kernel mode modified service routine  1202   d . Normally, this alternative requires recompilation and relinking of the modified application program. Thus, even an application which uses dynamic linking must be modified or else it will fail. In this alternative the verification of the signature can be made preferably by the kernel mode service routine  1202   d  (as in the previous alternatives), or by the standard library wrapper routine  1202   d.    
     As noted above, all the three alternatives of the first embodiment involve modification to the signature of one or more system calls. One example of such modification involves adding an extra parameter to the signature. In order to make it harder for attacker to break the secured system of the invention, the extra parameter may require a unique value adhering to the type of the relevant parameter (for example, a “magic number” in the case of a numeric parameter). The type of the one or more extra parameters and their unique values are also verified by the service routine at the kernel mode. 
     According to a second embodiment of the invention, the essential element which is modified is the dynamic linker of the operating system, and all the applications that access the dynamic linker are also modified to conform with said modification of the dynamic linker.  FIG. 4 a    describes the typical manner by which an application accesses a dynamic library. In typical systems, the application  700   a  which needs to access a dynamic library  720   a , uses the dynamic linker  710   a  which is provided by the operating system. The dynamic linker  710   a  loads the dynamic library  720   a  on behalf of the application  700   a.    
       FIG. 4 b    describes the second embodiment of the present invention. According to the second embodiment, the name of the dynamic linker  710   b  is modified in a manner unknown to authors of external applications. Furthermore, all the applications are modified to conform to said name modification of the dynamic linker in order to operate normally. External applications that have not been properly modified, will fail in loading dynamic libraries and will not operate. Optionally, the system further comprises a stub dynamic linker  705   b  which is kept under the original dynamic linker name. Under this option, when an unmodified application tries to use a dynamic library, it tries to use the dynamic linker  710   a  by its original name. This unmodified application will reach the stub  705   b  instead. Stub  705   b  will raise an alert with respect to the invalid operation of the external application. 
     According to a third embodiment of the invention, the essential elements that are modified are the names of one or more methods in a dynamic link library (DLL), and all the applications that access said dynamic link library are also modified to conform with said modification of the DLL.  FIG. 5 a    shows the typical manner by which an application  910   a  accesses a utility DLL  920   a .  FIG. 5 b    depicts the modifications made according to the third embodiment. The original utility DLL  920   b  is kept under a modified new name, while a proxy DLL  930   b  which implements the original DLL methods is kept under the name of the original DLL. One or more of the methods within the proxy DLL  930   b  are modified to raise an alert when they are called. For each modified method, the proxy DLL  930   b  supplies a renamed method which simply calls the original method within the renamed original utility DLL  920   b . Any application which originally used the utility DLL  920   a  is modified to call all the renamed methods by their modified name. Thus, an application which is modified will ultimately succeed in calling the appropriate method within the renamed original DLL  920   b , while any unmodified application will not only fail, but it will also be detected by the proxy DLL  930   b.    
     The underlying concept of the present invention as described above is not limited to the level of the operating system. It can also be implemented at the level of the instruction set. For example, the standard numeric code of one or more machine-level instructions may be altered in a manner unknown to authors of external programs, while preserving the original functionality of the instructions. This alteration can be obtained for example, by utilizing the “microcode update” facility which is available for modern AMD and Intel processors, or by using some other mechanism which allows such alterations. Alternatively, where a hypervisor is used, this alteration of the instruction set may be obtained by modifying the instruction set which is exposed by the hypervisor. When such low level modifications are made, the operating system along with useful benign programs should be patched to comply with the modified instruction set. 
       FIG. 6  depicts a fourth embodiment of the present invention, where modifications are made at the level of the instruction set. The standard numeric code of a given instruction  820  is replaced by a modified instruction code  810 , in a manner unknown to authors of external programs. Consequently, any program which is intended to use the modified instruction-set should be modified accordingly. When a modified program  800  issues a modified instruction code  810 , the processor goes on to execute the original instruction  820 . On the other hand, when an unmodified program  801  issues the unmodified instruction code  811 , the processor raises an exception  821 , which indicates an illegal operation. The term ‘processor’ in this context may refer either to a physical hardware processor, or to a virtual processor implemented by a hypervisor. 
     The following fifth embodiment of the invention is described in terms of Java or similar bytecode, where either a Virtual Machine (VM) or a Just In Time (JIT) compiler is applied.  FIG. 7 a    illustrates a first alternative of the fifth embodiment. Modified bytecode  7100  is processed by the modified Virtual Machine  7110 , and goes on to normal execution  7120 . On the other hand, when unmodified bytecode  7101  is processed by the modified Virtual Machine  7110 , an alert  7121  is raised, and the bytecode program is not executed. 
       FIG. 7 b    illustrates a second alternative of the fifth embodiment. Modified bytecode  7200  is processed by the modified JIT compiler  7210 , and is compiled into valid native machine code  7220 , which proceeds to normal execution  7230 . On the other hand, when an unmodified bytecode  7201  is processed by the modified JIT compiler  7210 , an alert  7221  is raised, and the bytecode program is not executed. 
     The invention as described above is particularly useful for cases where a central authorization agent is responsible for (a) all operation system modifications and installations; and (b) all applications modifications and installations. Examples for such cases are isolated systems, SCADA, and organizational cellular devices. 
     While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims.