_NSAKEY was a variable name discovered in Windows NT 4 SP5 in 1999 by Andrew D. Fernandes of Cryptonym Corporation. The variable contained a 1024-bit public key; public keys are used in public-key cryptography for encryption and digital signature verification (but not decryption or signing). Because of the name, however, it was speculated that the key would allow the United States National Security Agency (NSA) to subvert any Windows user's security. Microsoft denied the speculation and said that the key's name came from the fact that NSA was the technical review authority for U.S. cryptography export controls.
Overview Microsoft requires all Cryptographic Service Providers used by the Microsoft Cryptographic API (CryptoAPI) to have an RSA digital signature. Since only Microsoft-approved providers can be used with the CryptoAPI, it is possible to keep export copies of this operating system in compliance with the Export Administration Regulations (EAR), which are enforced by the Bureau of Industry and Security (BIS). It was already known that Microsoft used two keys, a primary and a spare, either of which can create valid signatures. Upon releasing the Service Pack 5 for Windows NT 4.0, Microsoft had neglected to remove the debugging symbols in ADVAPI32.DLL, a library that exposes such Windows features as Windows Registry and security. Andrew Fernandes, chief scientist with Cryptonym, found the primary key stored in the variable _KEY and the second key was labeled _NSAKEY. Fernandes published his discovery, touching off a flurry of speculation and conspiracy theories, including the possibility that the second key enabled the United States National Security Agency (NSA) to subvert any Windows user's security. During a presentation at the Computers, Freedom and Privacy 2000 (CFP2000) conference, Duncan Campbell, senior research fellow at the Electronic Privacy Information Center (EPIC), mentioned the _NSAKEY controversy as an example of an outstanding issue related to security and surveillance. In addition, Dr. Nicko van Someren found a third key in Windows 2000, which he doubted had a legitimate purpose, and declared that "It looks more fishy".
Microsoft's reaction Microsoft denied the backdoor speculations on _NSAKEY and said "This speculation is ironic since Microsoft has consistently opposed the various key escrow proposals suggested by the government." According to Microsoft, the key's symbol was "_NSAKEY" because the NSA was the review authority for U.S. cryptography export controls. Richard Purcell, Microsoft's Director of Corporate Privacy, approached Campbell after his presentation and expressed a wish to clear up the confusion and doubts about _NSAKEY. Immediately after the conference, Scott Culp, of the Microsoft Security Response Center, contacted Campbell and offered to answer his questions. Their correspondence began cordially but soon became strained; Campbell apparently felt Culp was being evasive and Culp apparently felt that Campbell was hostilely repeating questions that he had already answered. On 28 April 2000, Culp stated that "we have definitely reached the end of this discussion ... [which] is rapidly spiraling into the realm of conspiracy theory". Microsoft claimed the third key was only in beta builds of Windows 2000 and that its purpose was for signing Cryptographic Service Providers.
Further technical information The Mozilla page on common questions on cryptography describes how Microsoft signs CSPs:
It is in fact possible under certain circumstances to obtain an export license for software invoking cryptographic functions through an API. For example, Microsoft's implementation of the Microsoft Cryptographic API (CryptoAPI) specification was approved for export from the US, even though it implements an API by which third parties, including third parties outside the US, can add separate modules ("Cryptographic Service Providers" or CSPs) implementing cryptographic functionality. This export approval was presumably made possible because a) the CryptoAPI implementation requires third party CSPs to be digitally signed by Microsoft and rejects attempts to call CSPs not so signed; b) through this signing process Microsoft can ensure compliance with the relevant US export control regulations (e.g., they presumably would not sign a CSP developed outside the US that implements strong cryptography); and c) Microsoft's CryptoAPI implementation is available only in executable form, and thus is presumed to be reasonably resistant to user tampering to disable the CSP digital signature check.
According to Fernandes, it is possible to replace _NSAKEY. When loading a cryptographic module, the crypto_verify function first tries using _KEY to verify the module, then _NSAKEY. Since no cryptographic modules in Windows are signed with _NSAKEY, it never gets used. Replacing it with a different key allows non-US companies to install their crypto services into Windows without Microsoft's or the NSA's approval.
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