CryptGenRandom
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CryptGenRandom is a random number generator function that is included in Microsoft's Cryptographic Application Programming Interface. Microsoft recommends its use in all software where security is an issue.
[edit] Method of operation
All Microsoft-provided cryptography providers share the same implementation of CryptGenRandom, currently based on an internal function called RtlGenRandom. [1]. Only a general outline of the algorithm has been published as of 2006:
[RtlGenRandom] generates as specified in FIPS 186-2 appendix 3.1 with SHA-1 as the G function. And with entropy from:
[omitted: long lists of low-level system information fields and performance counters]
- The current process ID (GetCurrentProcessID).
- The current thread ID (GetCurrentThreadID).
- The tick count since boot time (GetTickCount).
- The current time (GetLocalTime).
- Various high-precision performance counters (QueryPerformanceCounter).
- An MD4 hash of the user's environment block, which includes username, computer name, and search path. [...]
- High-precision internal CPU counters, such as RDTSC, RDMSR, RDPMC
Source: Writing Secure Code, Second Edition. ISBN 0-7356-1722-8.
The exact algorithm has not been published, thus it is impossible for independent researchers to peer-review it and evaluate its effectiveness. Theoretical weaknesses include the use of outdated algorithms (such as MD4), and the reliance for entropy gathering on several monotonically-increasing counters that might be estimated or controlled to an extent by an attacker with local access to the machine.
