Add VERIFY_CHECKs and documentation that flags must be 0 or 1 #1783
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Flags for constant-time masking rely on the values being exactly 0 or 1 rather than 0 or true. Add VERIFY_CHECKs to enforce in VERIFY builds as a preventative measure and add documentation where relevant.
furszy
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Dec 9, 2025
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Wondering if it worth adding a macro for this; something like VERIFY_BOOL_ARG.
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Flags for constant-time masking rely on the values being exactly
0or1rather than0or true (any nonzero). One function,secp256k1_fe_cmovdocuments andVERIFY_CHECKs this, but most don't.This updates the documentation and adds
VERIFY_CHECKs enforcingflag == 0 || flag == 1for:secp256k1_fe_storage_cmovsecp256k1_gej_cmovsecp256k1_ge_storage_cmovsecp256k1_scalar_cadd_bitsecp256k1_scalar_cond_negatesecp256k1_scalar_cmovsecp256k1_int_cmov