Linux and Open-Source Applications

The building blocks for a secure and trustworthy computer platform.
Open-Source Operating Systems as a Solution

Open-source software offers a way out of this dilemma. If the source code is open, it can be inspected, and security holes can be found and fixed. Intentional security violations become much harder to hide and will almost certainly be discovered by the thousands of amateur and professional programmers on the Internet. If the source is truly open and widely distributed, flaws of all kinds will be discovered and announced on web sites and newsgroups. This form of interaction has proven remarkably effective in making Linux one of the most (if not the most) stable operating systems available.

With this type of public code review, can users be reasonably sure that Linux is trustworthy? Can users be sure that, if sufficient safeguards are incorporated into the OS, their data is secure? Linux had to be compiled using a compiler—what if the compiler was corrupted? It appears we now have to insist that even the compiler used to compile the OS should be open source. For truly concerned users, even that will not be enough, and a procedure involving multiple compilations on different platforms using different initial compilers would be required to produce the object code of the open-source compiler used to compile Linux.

Creating a Secure Linux Operating System and Compilers

In order to create a Linux build you can trust with sensitive information, you first need a compiler known not to insert hidden code as it compiles the operating system. How do you create a trusted compiler when starting off with compilers and operating systems that are not trustworthy? We propose the following as a possible sequence of steps.

  • Have thousands of programmers on the Internet inspect the source code of the compiler/linker, GNU C++.

  • Create an executable of the compiler/linker by compiling the source on a number of different platforms using different compilers and linkers.

  • Use the newly compiled compiler/linker executable on each of the different platforms to cross-compile themselves, as well as a number of different test programs, to a single platform such as x86.

  • The cross-compiled compiler/linker and sample program executables on each of the different platforms are then compared. If they are not identical under a byte-by-byte comparison, one or more of the newly generated compilers/linkers is probably subject to a security problem, and the system(s) and compiler source code should be investigated.

  • Assuming all the newly generated compiler and sample executables are identical, it can be asserted with a large degree of confidence that both the intermediary compiler/linker executables and the re-compiled compiler/linker executables are trustworthy.

Now that a safe version of GNU C++ has been created, the next step is to repeat the process to create a secure Linux build:

  • Have thousands of programmers on the Internet inspect the source code of the operating system, key system libraries, utilities and scripts.

  • Cross-compile executables of the operating system and its libraries/utilities to a common architecture (x86) using the trusted compilers.

  • Perform a byte-by-byte comparison of the executables and proclaim them trustworthy if they match.

  • Now, build a minimal Linux system installation using the trusted components, and gradually expand on the system's functionality by certifying all additional components.

Creating a Trustworthy Browser and Other Applications

As soon as a trusted Linux platform has been created, a similar process could be used to create a trusted browser. Because the browser is the application used to download other applications as well as communicate securely for e-commerce, it deserves special attention. To create a trusted browser:

  • Have thousands of programmers on the Internet inspect the source code.

  • Compile executables using a trusted platform and compiler.

  • Using a trusted compare utility (on CD-ROM), periodically compare CD-ROM versions of the executables of the operating system, compiler, utilities and applications (including the browser) with what is currently on the hard disk, just to ensure that an application hasn't used some hidden code to corrupt the platform.

Since Netscape Corp. has taken the initiative to open their browser code, Netscape would be the logical choice as a trusted browser. Ideally, all other applications to be used should be made trustworthy too, so the set of steps listed above should be carried out to create each new trusted application.

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