----- Forwarded message from Maxim Kammerer
This is not to say that RdRand is completely unusable. Putting RdRand entropy into a software pool implementation like /dev/urandom (or preferably, a higher-assurance multipool design like Fortuna) is a cheap way to prevent a putative backdoor from compromising your system state.
Nearly nothing from what you wrote is relevant to RDRAND, which is not a pure HWRNG, but implements CTR_DRBG with AES (unclear whether 128/192/256) from NIST SP 800-90A [1,2]. Interaction with hardware entropy source (ES) is implemented in microcode, so in case the relevant microcode is reverse-engineered (or relevant documentation obtained from Intel), it is possible to verify correctness of most of RDRAND operation. ES operation could be perhaps analyzed in a lab. The choice of CTR_DRBG over (probably much faster) Hash_DRBG seems weird on first sight, but secure hashes are not yet available in Intel processors [3]. Of course, an interesting conspiracy theory would then be that NSA influenced Intel to delay secure hash instructions deployment after breaking AES in order to exploit an AESNI-based RDRAND. [1] http://software.intel.com/en-us/articles/intel-digital-random-number-generat... [2] http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf [3] http://software.intel.com/en-us/articles/intel-sha-extensions -- Maxim Kammerer Liberté Linux: http://dee.su/liberte -- Liberationtech is a public list whose archives are searchable on Google. Violations of list guidelines will get you moderated: https://mailman.stanford.edu/mailman/listinfo/liberationtech. Unsubscribe, change to digest, or change password by emailing moderator at companys@stanford.edu. ----- End forwarded message ----- -- Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org ______________________________________________________________ ICBM: 48.07100, 11.36820 http://ativel.com http://postbiota.org AC894EC5: 38A5 5F46 A4FF 59B8 336B 47EE F46E 3489 AC89 4EC5