CryptGenRandom

CryptGenRandom is a deprecated cryptographically secure pseudorandom number generator function that is included in Microsoft CryptoAPI. In Win32 programs, Microsoft recommends its use anywhere random number generation is needed. A 2007 paper from Hebrew University suggested security problems in the Windows 2000 implementation of CryptGenRandom (assuming the attacker has control of the machine). Microsoft later acknowledged that the same problems exist in Windows XP, but not in Vista. Microsoft released a fix for the bug with Windows XP Service Pack 3 in mid-2008. The Win32 API includes comprehensive support for cryptographic security, including native TLS support (via the SCHANNEL API) and code signing. These capabilities are built on native Windows libraries for cryptographic operations, such as RSA and AES key generation. These libraries in turn rely on a cryptographically secure pseudorandom number generator (CSPRNG). CryptGenRandom is the standard CSPRNG for the Win32 programming environment. Microsoft-provided cryptography providers share the same implementation of CryptGenRandom, currently based on an internal function called RtlGenRandom. Only a general outline of the algorithm had been published : [RtlGenRandom] generates as specified in FIPS 186-2 appendix 3.1 with SHA-1 as the G function. And with entropy from: 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 [omitted: long lists of low-level system information fields and performance counters] The security of a cryptosystem's CSPRNG is significant because it is the origin for dynamic key material. Keys needed "on the fly", such as the AES TLS session keys that protect HTTPS sessions with bank websites, originate from CSPRNGs.