Why Microsoft ‘Shared Source’ can never be trusted

Trojan wars and Cold Wars

Yesterday we recounted the tale of how at the height of the Cold War Soviet infrastructure had been penetrated by software containing Trojans. Retired spook and nuclear scientist Thomas Reed claims that the United States provided compromised software to the USSR which detonated the Trans-Siberian gas pipeline. The Cold War's over, but we suggested that without an open toolchain - unless users could also inspect the source code for the tools used to build the OS - initiatives such as Microsoft's Shared Source program are worthless PR exercises.

But that's not quite right, as a few of you have pointed out. So let's correct that. Even with an open toolchain, initiatives such as Microsoft's Shared Source program are worthless PR exercises.

In 1984 the co-author of Unix Ken Thompson gave a theoretical example of how even an open toolchain could be compromised He described what he called the "cutetst program I ever wrote" in a paper subsequently known as Reflections on Trusting Trust. Thompson set about producing a program which produced as output an exact copy of its source, in other words a program that will create a self-reproducing program. His compromised compiler could be used to replace the standard UNIX compiler, and the intruder could then remove the traces from the compiler source code, knowing that any program generated by the compiler would harbor the Trojan.

Thompson's point was simple. "You can't trust code that you did not totally create yourself. No amount of source-level verification or scrutiny will protect you from using untrusted code," he pointed out.

The answer is to have a clean room environment - both tool chain and operating system - that the user has created and knows is free of compromises. This can then be trusted to bootstrap the toolchain and OS of your choice.

A reader casts doubt on Reed's claim and points out that the leading protagonists are "conveniently now dead". Reed could have been covering a genuine covert operation, or could be indulging in psyops in his retirement. You never know with spooks.

"In September," Mercury News reminds us today, "the governments of China, Japan and South Korea announced they would collaborate on developing an open-source alternative to Windows, citing cost and security benefits."

"Code for open-source software is freely available for anyone to download and modify. The Chinese government, concerned about security holes in Windows, favors a system it can customize and control."

For all of its educational benefits for the Chinese - and the programmers' comments evident the Windows source code recently on the Internet will certainly help expand their vernacular English - Shared Source doesn't help allay foreign governments' security concerns. And it probably never will. ®

Related Story

Explosive Cold War Trojan has lessons for Open Source exporters

External Link

Reflections on Trusting Trust - Ken Thompson

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