53 lines
1.1 KiB
C
53 lines
1.1 KiB
C
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#include "ge.h"
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static const fe d = {
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-10913610,13857413,-15372611,6949391,114729,-8787816,-6275908,-3247719,-18696448,-12055116
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} ;
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static const fe sqrtm1 = {
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-32595792,-7943725,9377950,3500415,12389472,-272473,-25146209,-2005654,326686,11406482
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} ;
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int ge_frombytes_negate_vartime(ge_p3 *h,const unsigned char *s)
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{
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fe u;
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fe v;
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fe v3;
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fe vxx;
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fe check;
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fe_frombytes(h->Y,s);
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fe_1(h->Z);
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fe_sq(u,h->Y);
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fe_mul(v,u,d);
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fe_sub(u,u,h->Z); /* u = y^2-1 */
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fe_add(v,v,h->Z); /* v = dy^2+1 */
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fe_sq(v3,v);
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fe_mul(v3,v3,v); /* v3 = v^3 */
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fe_sq(h->X,v3);
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fe_mul(h->X,h->X,v);
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fe_mul(h->X,h->X,u); /* x = uv^7 */
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fe_pow22523(h->X,h->X); /* x = (uv^7)^((q-5)/8) */
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fe_mul(h->X,h->X,v3);
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fe_mul(h->X,h->X,u); /* x = uv^3(uv^7)^((q-5)/8) */
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fe_sq(vxx,h->X);
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fe_mul(vxx,vxx,v);
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fe_sub(check,vxx,u); /* vx^2-u */
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if (fe_isnonzero(check)) {
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fe_add(check,vxx,u); /* vx^2+u */
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if (fe_isnonzero(check)) return -1;
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fe_mul(h->X,h->X,sqrtm1);
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}
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if (fe_isnegative(h->X) == (s[31] >> 7))
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fe_neg(h->X,h->X);
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fe_mul(h->T,h->X,h->Y);
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return 0;
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}
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