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Fix a timing leak in ecp_mul_mxz() - 2.28 backport #6492

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merged 1 commit into from
Oct 27, 2022
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Fix a timing leak in ecp_mul_mxz() - 2.28 backport #6492

merged 1 commit into from
Oct 27, 2022
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@daverodgman daverodgman commented Oct 27, 2022 •
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Trivial backport of #5841
Changelog: Not needed

@aurel32 @daverodgman
Fix a timing leak in ecp_mul_mxz()
edc110d 
The bit length of m is leaked through through timing in ecp_mul_mxz().
Initially found by Manuel Pégourié-Gonnard on ecp_mul_edxyz(), which has
been inspired from ecp_mul_mxz(), during initial review of the EdDSA PR.
See: Mbed-TLS#3245 (comment)

Fix that by using grp->nbits + 1 instead, which anyway is very close to
the length of m, which means there is no significant performance impact.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
@daverodgman daverodgman mentioned this pull request Oct 27, 2022
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@daverodgman daverodgman changed the title Fix a timing leak in ecp_mul_mxz() Fix a timing leak in ecp_mul_mxz() - 2.28 backport Oct 27, 2022
@daverodgman daverodgman requested a review from mpg October 27, 2022 11:01
@daverodgman daverodgman added bug needs-review Every commit must be reviewed by at least two team members, needs-ci Needs to pass CI tests size-s Estimated task size: small (~2d) single-reviewer This PR qualifies for having only one reviewer priority-medium Medium priority - this can be reviewed as time permits component-crypto Crypto primitives and low-level interfaces and removed needs-ci Needs to pass CI tests labels Oct 27, 2022
@daverodgman daverodgman removed the request for review from mpg October 27, 2022 16:39
@daverodgman daverodgman added the needs-reviewer This PR needs someone to pick it up for review label Oct 27, 2022
gilles-peskine-arm
gilles-peskine-arm approved these changes Oct 27, 2022
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Approved as a faithful backport of #5841, no need to do anything different in 2.28.

@gilles-peskine-arm gilles-peskine-arm added approved Design and code approved - may be waiting for CI or backports and removed needs-review Every commit must be reviewed by at least two team members, needs-reviewer This PR needs someone to pick it up for review labels Oct 27, 2022
@gilles-peskine-arm gilles-peskine-arm merged commit e0917c0 into Mbed-TLS:mbedtls-2.28 Oct 27, 2022
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approved Design and code approved - may be waiting for CI or backports bug component-crypto Crypto primitives and low-level interfaces priority-medium Medium priority - this can be reviewed as time permits single-reviewer This PR qualifies for having only one reviewer size-s Estimated task size: small (~2d)
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