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60 lines
1.9 KiB
C
60 lines
1.9 KiB
C
#include "cbd.h"
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/*************************************************
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* Name: load_littleendian
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*
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* Description: load bytes into a 64-bit integer
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* in little-endian order
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*
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* Arguments: - const unsigned char *x: pointer to input byte array
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* - bytes: number of bytes to load, has to be <=
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*8
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*
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* Returns 64-bit unsigned integer loaded from x
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**************************************************/
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static uint64_t load_littleendian(const unsigned char *x, int bytes) {
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int i;
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uint64_t r = x[0];
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for (i = 1; i < bytes; i++) {
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r |= (uint64_t)x[i] << (8 * i);
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}
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return r;
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}
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/*************************************************
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* Name: cbd
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*
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* Description: Given an array of uniformly random bytes, compute
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* polynomial with coefficients distributed according to
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* a centered binomial distribution with parameter KYBER_ETA
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*
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* Arguments: - poly *r: pointer to output polynomial
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* - const unsigned char *buf: pointer to input byte array
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**************************************************/
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void PQCLEAN_KYBER768_CLEAN_cbd(poly *r, const unsigned char *buf) {
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uint32_t t, d, a[4], b[4];
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int i, j;
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for (i = 0; i < KYBER_N / 4; i++) {
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t = (uint32_t)load_littleendian(buf + 4 * i, 4);
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d = 0;
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for (j = 0; j < 4; j++) {
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d += (t >> j) & 0x11111111;
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}
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a[0] = d & 0xf;
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b[0] = (d >> 4) & 0xf;
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a[1] = (d >> 8) & 0xf;
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b[1] = (d >> 12) & 0xf;
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a[2] = (d >> 16) & 0xf;
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b[2] = (d >> 20) & 0xf;
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a[3] = (d >> 24) & 0xf;
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b[3] = (d >> 28);
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r->coeffs[4 * i + 0] = (uint16_t)(a[0] + KYBER_Q - b[0]);
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r->coeffs[4 * i + 1] = (uint16_t)(a[1] + KYBER_Q - b[1]);
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r->coeffs[4 * i + 2] = (uint16_t)(a[2] + KYBER_Q - b[2]);
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r->coeffs[4 * i + 3] = (uint16_t)(a[3] + KYBER_Q - b[3]);
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}
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}
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