NSAKEY

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.

Further speculation

Microsoft stated that the second key is present as a backup to guard against the possibility of losing the primary secret key. Fernandes doubts this explanation, pointing out that the generally accepted way to guard against loss of a secret key is secret splitting, which would divide the key into several different parts, which would then be distributed throughout senior management. He stated that this would be far more robust than using two keys; if the second key is also lost, Microsoft would need to patch or upgrade every copy of Windows in the world, as well as every cryptographic module it had ever signed.

On the other hand, if Microsoft failed to think about the consequences of key loss and created a first key without using secret splitting (and did so in secure hardware which doesn't allow protection to be weakened after key generation), and the NSA pointed out this problem as part of the review process, it might explain why Microsoft weakened their scheme with a second key and why the new one was called _NSAKEY. (The second key might be backed up using secret splitting, so losing both keys should not be a problem.) Another possibility is that Microsoft included a second key to be able to sign cryptographic modules outside the United States, while still complying with the BIS's EAR. If cryptographic modules were to be signed in multiple locations, using multiple keys is a reasonable approach. However, no cryptographic module has ever been found to be signed by _NSAKEY, and Microsoft denies that any other certification authority exists.

Bruce Schneier believes that the above type of concern, i.e. NSA putting a key in Windows so it can load arbitrary backdoored CSPs, is unfounded. He argues that there are easier ways of backdooring Windows that do not involve using an additional key, let alone one called "NSAKEY" in debug symbols visible to the whole company: the NSA could just ask for the main key. The crypto API is also a poor point of entry, as it requires the victim to run an NSA-supplied executable.

Key values

Both keys are RSA keys with an e equal to 65537, which is a standard choice.

_KEY has an n of:

b273e277a9c375c70bb7493e52b0b36962e976626ad609ba31be6accac12f1f3da6c18d96951820c457c7b4c4893bd149de279a39f6ec926d3544db3491fa2e9af1bf8260b3b0fbadd69cbd77b28012925711b17c0b877eaf7da9d02dd5f8572854e5c90e9b10cfbaeaf8b8fe1df5047bc18829a531499bbf49e8021346b5095

_NSAKEY has an n of:

ba8e15fee3cd160fb47cf93e2b4d842615af23f0659264d81edc35a27d3aa450890a227b561da401ff3908771d243f6eeb4f9e351976e90f07fd22cd099ccd71e85b97f5439adb172d32d71cb66c26c5b188a3e11790ed01eb31bf27bc667b396fd8283097d8b3869cc7511a3496e829a32bbad6d2f7aa7e8ca9805d51682d1f

PGP keys

In September 1999, an anonymous researcher reverse-engineered both the primary key and the _NSAKEY into PGP-compatible format and published them to key servers.

Primary key (_KEY)

Type Bits/KeyID Date User ID pub 1024/346B5095 1999/09/06 Microsoft's CAPI key <[email protected]> -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.3i mQCPAzfTc8YAAAEEALJz4nepw3XHC7dJPlKws2li6XZiatYJujG+asysEvHz2mwY 2WlRggxFfHtMSJO9FJ3ieaOfbskm01RNs0kfoumvG/gmCzsPut1py9d7KAEpJXEb F8C4d+r32p0C3V+FcoVOXJDpsQz7rq+Lj+HfUEe8GIKaUxSZu/SegCE0a1CVABEB AAG0L01pY3Jvc29mdCdzIENBUEkga2V5IDxwb3N0bWFzdGVyQG1pY3Jvc29mdC5j b20+iQEVAwUQN9Nz5j57yqgoskVRAQFr/gf8DGm1hAxWBmx/0bl4m0metM+IM39J yI5mub0ie1HRLExP7lVJezBTyRryV3tDv6U3OIP+KZDthdXb0fmGU5z+wHt34Uzu xl6Q7m7oB76SKfNaWgosZxqkE5YQrXXGsn3oVZhV6yBALekWtsdVaSmG8+IJNx+n NvMTYRUz+MdrRFcEFDhFntblI8NlQenlX6CcnnfOkdR7ZKyPbVoSXW/Z6q7U9REJ TSjBT0swYbHX+3EVt8n2nwxWb2ouNmnm9H2gYfXHikhXrwtjK2aG/3J7k6EVxS+m Rp+crFOB32sTO1ib2sr7GY7CZUwOpDqRxo8KmQZyhaZqz1x6myurXyw3Tg== =ms8C -----END PGP PUBLIC KEY BLOCK-----

Secondary key (_NSAKEY and _KEY2)

Type Bits/KeyID Date User ID pub 1024/51682D1F 1999/09/06 NSA's Microsoft CAPI key <[email protected]> -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.3i mQCPAzfTdH0AAAEEALqOFf7jzRYPtHz5PitNhCYVryPwZZJk2B7cNaJ9OqRQiQoi e1YdpAH/OQh3HSQ/butPnjUZdukPB/0izQmczXHoW5f1Q5rbFy0y1xy2bCbFsYij 4ReQ7QHrMb8nvGZ7OW/YKDCX2LOGnMdRGjSW6CmjK7rW0veqfoypgF1RaC0fABEB AAG0LU5TQSdzIE1pY3Jvc29mdCBDQVBJIGtleSA8cG9zdG1hc3RlckBuc2EuZ292 PokBFQMFEDfTdJE+e8qoKLJFUQEBHnsH/ihUe7oq6DhU1dJjvXWcYw6p1iW+0euR YfZjwpzPotQ8m5rC7FrJDUbgqQjoFDr++zN9kD9bjNPVUx/ZjCvSFTNu/5X1qn1r it7IHU/6Aem1h4Bs6KE5MPpjKRxRkqQjbW4f0cgXg6+LV+V9cNMylZHRef3PZCQa 5DOI5crQ0IWyjQCt9br07BL9C3X5WHNNRsRIr9WiVfPK8eyxhNYl/NiH2GzXYbNe UWjaS2KuJNVvozjxGymcnNTwJltZK4RLZxo05FW2InJbtEfMc+m823vVltm9l/f+ n2iYBAaDs6I/0v2AcVKNy19Cjncc3wQZkaiIYqfPZL19kT8vDNGi9uE= =PhHT -----END PGP PUBLIC KEY BLOCK-----