[openssl-dev] DRBG entropy

[Leon Brits]

Hi all,

I have a chip (FDK RPG100) that generates randomness, but the SP800-90B python test suite indicated that the chip only provides 2.35 bits/byte of entropy. According to FIPS test lab the lowest value from all the tests are used as the entropy and 2 is too low. I must however make use of this chip.

Looking at the paragraph in the User Guide 2.0 where low entropy sources are discussed and have some additional questions:

1.     In my DRBG callback for entropy (function get_entropy in the guide), I simply used our chip as the source (the driver reading from the chip, makes it available at /dev/hwrng). Now that I've come to learn that the chip's entropy is too low, how do I ensure that this callback exists with a buffer of acceptable entropy?

2.     Should I just return a 4 times larger buffer? Wat if that is larger than the "max_len"?

3.     Can the DRBG repeatedly call the callback until the entropy is high enough?

Your advice is appreciated

Regards
LJB
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