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由 Nicola Tuveri 提交于
for specialized Montgomery ladder implementations PR #6009 and #6070 replaced the default EC point multiplication path for prime and binary curves with a unified Montgomery ladder implementation with various timing attack defenses (for the common paths when a secret scalar is feed to the point multiplication). The newly introduced default implementation directly used EC_POINT_add/dbl in the main loop. The scaffolding introduced by this commit allows EC_METHODs to define a specialized `ladder_step` function to improve performances by taking advantage of efficient formulas for differential addition-and-doubling and different coordinate systems. - `ladder_pre` is executed before the main loop of the ladder: by default it copies the input point P into S, and doubles it into R. Specialized implementations could, e.g., use this hook to transition to different coordinate systems before copying and doubling; - `ladder_step` is the core of the Montgomery ladder loop: by default it computes `S := R+S; R := 2R;`, but specific implementations could, e.g., implement a more efficient formula for differential addition-and-doubling; - `ladder_post` is executed after the Montgomery ladder loop: by default it's a noop, but specialized implementations could, e.g., use this hook to transition back from the coordinate system used for optimizing the differential addition-and-doubling or recover the y coordinate of the result point. This commit also renames `ec_mul_consttime` to `ec_scalar_mul_ladder`, as it better corresponds to what this function does: nothing can be truly said about the constant-timeness of the overall execution of this function, given that the underlying operations are not necessarily constant-time themselves. What this implementation ensures is that the same fixed sequence of operations is executed for each scalar multiplication (for a given EC_GROUP), with no dependency on the value of the input scalar. Co-authored-by: NSohaib ul Hassan <soh.19.hassan@gmail.com> Co-authored-by: NBilly Brumley <bbrumley@gmail.com> Reviewed-by: NAndy Polyakov <appro@openssl.org> Reviewed-by: NMatt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/6690)
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