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This adds some of the ground work for hardware backed brute force resistance on Cr50. The feature is called Pinweaver. It will initially be used to enable PIN authentication on CrOS devices without reducing the security of the platform. A Merkle tree is used to validate encrypted metadata used to track login attempts. The metadata tracks counts of failed attempts, a timestamp of the last failed attempt, the secrets, and any associated parameters. Instead of storing the metadata on Cr50 an AES-CTR is used with an HMAC to encrypt the data so it can be stored off-chip and loaded when needed. The Merkle tree is used to track the current state of all the metadata to prevent replay attacks of previously exported copies. It is a tree of hashes whose root hash is stored on Cr50, and whose leaves are the HMACs of the encrypted metadata. BRANCH=none BUG=chromium:809730, chromium:809741, chromium:809743, chromium:809747 TEST=cd ~/src/platform/ec && V=1 make run-pinweaver -j Change-Id: Id10bb49d8ebc5a487dd90c6093bc0f51dadbd124 Signed-off-by: Allen Webb <allenwebb@google.com> Reviewed-on: https://chromium-review.googlesource.com/895395 Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>