g: RSA randomization
Split bn_modexp() into three variants:
bn_modexp() for large exponents (as before)
bn_modexp_word() for single word public exponents
bn_modexp_blinded() for large exponents w/ randomization
We randomize bn_modexp_blinded() with:
1) pick 64 bit random R1 and compute R1 ** -1 and R1 ** pubexp, mod N.
2) multiply input by R1 ** pubexp
3) pick 64 bit random R2 and add (e*d*R2 - R2) to private exponent (i.e.
a random multiple of phi(N))
4) exponentiate
5) multiply output w/ R1 ** -1 to obtain expected result
Since we enlarge the exponent, bn_modexp_blinded() is slower than
bn_modexp(). We only use bn_modexp_blinded() when private exponents are
in play and we have phi(N) available.
Also refactored the combined p256 and rsa dcrypto binary blob into two
parts. And added unique first word to each dcrypto blob to make code
caching reliable.
The TPM task stack maxes out at 8040/8192 in tcg_test due to increased
stack usage of bn_modexp_blinded() but is still within safe bounds,
with 88 byte redzone.
BRANCH=cr50
BUG=b:35587382,b:35587381
TEST=buildall, tcg_test (200+)
Change-Id: Ied1f908418f31f8025363179537aa4ebd2c80420
Reviewed-on: https://chromium-review.googlesource.com/540684
Reviewed-by: Marius Schilder <mschilder@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
Tested-by: Marius Schilder <mschilder@chromium.org>
8 files changed
