Classic McEliece Side Channel Report #204
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Ready for integration and review |
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Thanks a lot Failing CI is due to the missing #203. No problem for now, but please rebase to latest |
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Never mind! It interfered with some other changes while integrating, so I just went ahead and rebased your commits onto |
| private: | ||
| constexpr bitref& assign(bool bit) noexcept { | ||
| const block_type assign_mask = 0 - static_cast<block_type>(bit); | ||
| this->m_block \|= (this->m_mask & assign_mask); | ||
| this->m_block &= ~(this->m_mask & ~assign_mask); | ||
| return \*this; | ||
| } |
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We fixed the side channel using Botan's constant time helper class CT::Mask, which is more readable, in my opinion and does similar things as this code block. I guess your code translates better to assembly, though. So I'm fine with you version. (So nothing to do here, just a comment)
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It's probably worth mentioning that the later (and final) versions of the code fix this side channel
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Note added in 5df0aa0
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Co-authored-by: Fabian Albert <fabian.albert@rohde-schwarz.com>
Not yet ready for review