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https://github.com/henrydcase/pqc.git
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51 lines
1.5 KiB
C
51 lines
1.5 KiB
C
#include "verify.h"
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#include <stddef.h>
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#include <stdint.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 uint8_t *a: pointer to first byte array
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* const uint8_t *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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uint8_t PQCLEAN_KYBER76890S_CLEAN_verify(const uint8_t *a, const uint8_t *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 (uint8_t)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: uint8_t *r: pointer to output byte array
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* const uint8_t *x: pointer to input byte array
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* size_t len: Amount of bytes to be copied
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* uint8_t b: Condition bit; has to be in {0,1}
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**************************************************/
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void PQCLEAN_KYBER76890S_CLEAN_cmov(uint8_t *r, const uint8_t *x, size_t len, uint8_t 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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