Re: Entropy sources under WinXP

David Wagner wrote:

Sebastian G. wrote:
Yes, and that's the problem. Well, only for values of a type that has no size limit, and Rng\Seed sadly is such a type.

Ouch. That sucks. Sounds like it could affect many registry
entries, not just the rng seed.

Does MS provide no safe way to access the registry?


They do. F.e. REG_*SZ is limited in size, and most REG_BINARY values are also limited. Typically it's sufficient to use a buffer of 64K size and trim it down based on the expected size. For the entries of HKEY_DYN_DATA, they added special locks. On Windows Vista, they added transactional semantics for a set of operations.

Rng\Seed however is unlimited, as it acts as an entropy pool.

But as I said: Why should you care? CryptGenRandom and CryptAddRandom are safe API functions which allow you to access this RNG seed without any worries. The job is carried out by the Cryptography Service Provider service, which as a system service has sufficient privilege to simply imposing a lock on this key. The location and the value might even change among versions, but the API will transparently reflect these changes.

Are the access control permissions to Rng\Seed restricted tightly enough
that one can analyze all apps that have the power to write


Rng\Seed is read-only for non-admin users.


.

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