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de5cda4d7b
https://github.com/mupq/pqm4/issues/132 repoorted that the NewHope verify function does not actually return 0 or 1, but 0 or -1, which consequenctly breaks the cmov in the FO transform. This bug was introduced when I integrated this into PQClean.
27 lines
828 B
C
27 lines
828 B
C
#include "reduce.h"
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#include "params.h"
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static const uint32_t qinv = 12287; // -inverse_mod(p,2^18)
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static const uint32_t rlog = 18;
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/*************************************************
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* Name: montgomery_reduce
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*
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* Description: Montgomery reduction; given a 32-bit integer a, computes
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* 16-bit integer congruent to a * R^-1 mod q,
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* where R=2^18 (see value of rlog)
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*
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* Arguments: - uint32_t a: input unsigned integer to be reduced; has to be in {0,...,1073491968}
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*
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* Returns: unsigned integer in {0,...,2^14-1} congruent to a * R^-1 modulo q.
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**************************************************/
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uint16_t PQCLEAN_NEWHOPE512CCA_CLEAN_montgomery_reduce(uint32_t a) {
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uint32_t u;
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u = (a * qinv);
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u &= ((1 << rlog) - 1);
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u *= NEWHOPE_Q;
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a = a + u;
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return a >> 18;
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}
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