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.
50 lines
1.6 KiB
C
50 lines
1.6 KiB
C
#include "verify.h"
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#include <stdint.h>
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#include <string.h>
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/*************************************************
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* Name: verify
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*
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* Description: Compare two arrays for equality in constant time.
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*
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* Arguments: const unsigned char *a: pointer to first byte array
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* const unsigned char *b: pointer to second byte array
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* size_t len: length of the byte arrays
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*
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* Returns 0 if the byte arrays are equal, 1 otherwise
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**************************************************/
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int PQCLEAN_NEWHOPE512CCA_CLEAN_verify(const unsigned char *a, const unsigned char *b, size_t len) {
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uint64_t r;
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size_t i;
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r = 0;
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for (i = 0; i < len; i++) {
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r |= a[i] ^ b[i];
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}
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r = (-r) >> 63;
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return (int)r;
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}
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/*************************************************
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* Name: cmov
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*
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* Description: Copy len bytes from x to r if b is 1;
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* don't modify x if b is 0. Requires b to be in {0,1};
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* assumes two's complement representation of negative integers.
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* Runs in constant time.
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*
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* Arguments: unsigned char *r: pointer to output byte array
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* const unsigned char *x: pointer to input byte array
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* size_t len: Amount of bytes to be copied
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* unsigned char b: Condition bit; has to be in {0,1}
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**************************************************/
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void PQCLEAN_NEWHOPE512CCA_CLEAN_cmov(unsigned char *r, const unsigned char *x, size_t len, unsigned char b) {
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size_t i;
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b = -b;
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for (i = 0; i < len; i++) {
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r[i] ^= b & (x[i] ^ r[i]);
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}
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}
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