-rw-r--r-- 2335 lib25519-20221222/crypto_mGnP/ed25519/ref10/ge_double_scalarmult.c raw
#include "ge.h" #include "Bi.h" static void slide(signed char *r,const unsigned char *a) { int i; int b; int k; for (i = 0;i < 256;++i) r[i] = 1 & (a[i >> 3] >> (i & 7)); for (i = 0;i < 256;++i) if (r[i]) { for (b = 1;b <= 6 && i + b < 256;++b) { if (r[i + b]) { if (r[i] + (r[i + b] << b) <= 15) { r[i] += r[i + b] << b; r[i + b] = 0; } else if (r[i] - (r[i + b] << b) >= -15) { r[i] -= r[i + b] << b; for (k = i + b;k < 256;++k) { if (!r[k]) { r[k] = 1; break; } r[k] = 0; } } else break; } } } } /* r = a * A + b * B where a = a[0]+256*a[1]+...+256^31 a[31]. and b = b[0]+256*b[1]+...+256^31 b[31]. B is the Ed25519 base point (x,4/5) with x positive. */ void ge_double_scalarmult_vartime(ge_p2 *r,const unsigned char *a,const ge_p3 *A,const unsigned char *b) { signed char aslide[256]; signed char bslide[256]; ge_cached Ai[8]; /* A,3A,5A,7A,9A,11A,13A,15A */ ge_p1p1 t; ge_p3 u; ge_p3 A2; int i; slide(aslide,a); slide(bslide,b); ge_p3_to_cached(&Ai[0],A); ge_p3_dbl(&t,A); ge_p1p1_to_p3(&A2,&t); ge_add(&t,&A2,&Ai[0]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[1],&u); ge_add(&t,&A2,&Ai[1]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[2],&u); ge_add(&t,&A2,&Ai[2]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[3],&u); ge_add(&t,&A2,&Ai[3]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[4],&u); ge_add(&t,&A2,&Ai[4]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[5],&u); ge_add(&t,&A2,&Ai[5]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[6],&u); ge_add(&t,&A2,&Ai[6]); ge_p1p1_to_p3(&u,&t); ge_p3_to_cached(&Ai[7],&u); ge_p2_0(r); for (i = 255;i >= 0;--i) { if (aslide[i] || bslide[i]) break; } for (;i >= 0;--i) { ge_p2_dbl(&t,r); if (aslide[i] > 0) { ge_p1p1_to_p3(&u,&t); ge_add(&t,&u,&Ai[aslide[i]/2]); } else if (aslide[i] < 0) { ge_p1p1_to_p3(&u,&t); ge_sub(&t,&u,&Ai[(-aslide[i])/2]); } if (bslide[i] > 0) { ge_p1p1_to_p3(&u,&t); ge_madd(&t,&u,&Bi[bslide[i]/2]); } else if (bslide[i] < 0) { ge_p1p1_to_p3(&u,&t); ge_msub(&t,&u,&Bi[(-bslide[i])/2]); } ge_p1p1_to_p2(r,&t); } }