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eccp2.c
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/****************************************************************************************
* FourQlib: a high-performance crypto library based on the elliptic curve FourQ
*
* Copyright (c) Microsoft Corporation. All rights reserved.
*
* Abstract: ECC operations over GF(p^2) exploiting endomorphisms
*
* This code is based on the papers:
* [1] "FourQ: four-dimensional decompositions on a Q-curve over the Mersenne prime"
* by Craig Costello and Patrick Longa, ASIACRYPT2015 (http://eprint.iacr.org/2015/565).
* [2] "FourQNEON: Faster Elliptic Curve Scalar Multiplications on ARM Processors"
* by Patrick Longa, SAC2016 (http://eprint.iacr.org/2016/645).
******************************************************************************************/
#include "FourQ_internal.h"
#include "FourQ_params.h"
#include "FourQ_tables.h"
#include "ARM/fp_arm.h"
#include <arm_neon.h>
/***********************************************/
/************* GF(p^2) FUNCTIONS ***************/
void fp2copy1271(f2elm_t a, f2elm_t c)
{ // Copy of a GF(p^2) element, c = a
fpcopy1271(a[0], c[0]);
fpcopy1271(a[1], c[1]);
}
void v2copy1271(v2elm_t a, v2elm_t c)
{ // Copy vectorized GF(p^2) element, c <- a
c[0] = a[0]; c[1] = a[1]; c[2] = a[2]; c[3] = a[3]; c[4] = a[4];
c[5] = a[5]; c[6] = a[6]; c[7] = a[7]; c[8] = a[8]; c[9] = a[9];
}
void v2zero1271(v2elm_t a)
{ // Zeroing vectorized GF(p^2) element, a = 0
a[0] = 0; a[1] = 0; a[2] = 0; a[3] = 0; a[4] = 0;
a[5] = 0; a[6] = 0; a[7] = 0; a[8] = 0; a[9] = 0;
}
__inline void v2add1271(v2elm_t a, v2elm_t b, v2elm_t c)
{ // Vectorized GF(p^2) addition, c = a+b in GF((2^127-1)^2)
v2add1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c);
}
__inline void v2sub1271(v2elm_t a, v2elm_t b, v2elm_t c)
{ // Vectorized GF(p^2) subtraction, c = a-b in GF((2^127-1)^2)
v2sub1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c);
}
void v2dblsub1271(v2elm_t a, v2elm_t b, v2elm_t c)
{ // Vectorized GF(p^2) addition followed by subtraction, c = 2a-b in GF((2^127-1)^2)
v2dblsub1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c);
}
void v2addsub1271(v2elm_t a, v2elm_t b, v2elm_t c, v2elm_t d)
{ // Vectorized GF(p^2) addition and subtraction, c = a+b, d = a-b in GF((2^127-1)^2)
v2addsub1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c, (uint32_t*)d);
}
void v2neg1271(v2elm_t a)
{ // Vectorized GF(p^2) negation
// Representation: 23/23/26/26/26/26/26/26/26/26-bit
a[0] = mask_26 - a[0];
a[1] = mask_26 - a[1];
a[2] = mask_26 - a[2];
a[3] = mask_26 - a[3];
a[4] = mask_26 - a[4];
a[5] = mask_26 - a[5];
a[6] = mask_26 - a[6];
a[7] = mask_26 - a[7];
a[8] = mask_23 - a[8];
a[9] = mask_23 - a[9];
}
void v2mul1271(v2elm_t a, v2elm_t b, v2elm_t c)
{ // Vectorized GF(p^2) multiplication, c = a*b in GF((2^127-1)^2)
v2mul1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c);
}
void v2sqr1271(v2elm_t a, v2elm_t c)
{ // Vectorized GF(p^2) squaring, c = a^2 in GF((2^127-1)^2)
v2sqr1271_a((uint32_t*)a, (uint32_t*)c);
}
#if defined(MIX_ARM_NEON)
void v2muladd1271(v2elm_t a, v2elm_t b, v2elm_t c, v2elm_t d, v2elm_t e, v2elm_t f)
{ // Vectorized GF(p^2) multiplication/addition in GF((2^127-1)^2)
v2muladd1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c, (uint32_t*)d, (uint32_t*)e, (uint32_t*)f);
}
void v2mulsub1271(v2elm_t a, v2elm_t b, v2elm_t c, v2elm_t d, v2elm_t e, v2elm_t f)
{ // Vectorized GF(p^2) multiplication/subtraction in GF((2^127-1)^2)
v2mulsub1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c, (uint32_t*)d, (uint32_t*)e, (uint32_t*)f);
}
void v2muladdsub1271(v2elm_t a, v2elm_t b, v2elm_t c, v2elm_t d, v2elm_t e, v2elm_t f, v2elm_t g)
{ // Vectorized GF(p^2) multiplication/addition/subtraction in GF((2^127-1)^2)
v2muladdsub1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c, (uint32_t*)d, (uint32_t*)e, (uint32_t*)f, (uint32_t*)g);
}
void v2muldblsub1271(v2elm_t a, v2elm_t b, v2elm_t c, v2elm_t d, v2elm_t e, v2elm_t f)
{ // Vectorized GF(p^2) multiplication/addition/subtraction in GF((2^127-1)^2)
v2muldblsub1271_a((uint32_t*)a, (uint32_t*)b, (uint32_t*)c, (uint32_t*)d, (uint32_t*)e, (uint32_t*)f);
}
void v2sqradd1271(v2elm_t a, v2elm_t c, v2elm_t d, v2elm_t e, v2elm_t f)
{ // Vectorized GF(p^2) squaring/addition in GF((2^127-1)^2)
v2sqradd1271_a((uint32_t*)a, (uint32_t*)c, (uint32_t*)d, (uint32_t*)e, (uint32_t*)f);
}
void v2sqraddsub1271(v2elm_t a, v2elm_t c, v2elm_t d, v2elm_t e, v2elm_t f, v2elm_t g)
{ // Vectorized GF(p^2) squaring/addition/subtraction in GF((2^127-1)^2)
v2sqraddsub1271_a((uint32_t*)a, (uint32_t*)c, (uint32_t*)d, (uint32_t*)e, (uint32_t*)f, (uint32_t*)g);
}
#endif
void v2inv1271(v2elm_t a)
{ // Vectorized GF(p^2) inversion, a = (a0-i*a1)/(a0^2+a1^2)
velm_t a0, a1, t0, t1;
from_v2_to_v(a, a0, a1);
vsqr1271(a0, t0); // t0 = a0^2
vsqr1271(a1, t1); // t1 = a1^2
vadd1271(t0, t1, t0); // t0 = a0^2+a1^2
vinv1271(t0); // t0 = (a0^2+a1^2)^-1
vneg1271(a1); // a = a0-i*a1
vmul1271(a0, t0, a0);
vmul1271(a1, t0, a1); // a = (a0-i*a1)*(a0^2+a1^2)^-1
from_v_to_v2(a0, a1, a);
}
__inline void clear_words(void* mem, unsigned int nwords)
{ // Clear integer-size digits from memory. "nwords" indicates the number of integer digits to be zeroed.
// This function uses the volatile type qualifier to inform the compiler not to optimize out the memory clearing.
// It has been tested with MSVS 2013 and GNU GCC 4.6.3, 4.7.3, 4.8.2 and 4.8.4. Users are responsible for verifying correctness with different compilers.
// See "Compliant Solution (C99)" at https://www.securecoding.cert.org/confluence/display/c/MSC06-C.+Beware+of+compiler+optimizations
unsigned int i;
volatile unsigned int *v = mem;
for (i = 0; i < nwords; i++)
v[i] = 0;
}
#if (USE_ENDO == true)
// Fixed GF(p^2) constants for the endomorphisms
static v2elm_t ctau1 = {0x3ce74c3, 0x12, 0x3355f3a, 0x0, 0x120c74d, 0xc000, 0xb0ebeb, 0x0, 0x1964de, 0x0};
static v2elm_t ctaudual1 = {0x2cdf034, 0x11, 0x2a9b677, 0x0, 0x6529ec, 0x3ff4000, 0x3ac8c16, 0x3ffffff, 0x4aa740, 0x7fffff};
static v2elm_t cphi0 = {0x3fffff7,0x366f81a, 0x3ffffff, 0x154db3b, 0x5fff, 0x3294f6, 0x0, 0x1d6460b, 0x0, 0x2553a0};
static v2elm_t cphi1 = {0x7, 0x28296f9, 0x0, 0x3643a78, 0x5000, 0x22cf334, 0x0, 0x2831431, 0x0, 0x62c8ca};
static v2elm_t cphi2 = {0x15, 0x31df391, 0x0, 0x32dc553, 0xf000, 0x1c982c2, 0x0, 0xadb26d, 0x0, 0x78df26};
static v2elm_t cphi3 = {0x3,0x3962ea4, 0x0, 0x10115e9, 0x2000, 0x342a924, 0x0, 0x12475d8, 0x0, 0x5084c6};
static v2elm_t cphi4 = {0x3, 0x2ec6855, 0x0, 0x263248e, 0x3000, 0x2ea4a10, 0x0, 0x15e9e58, 0x0, 0x124404};
static v2elm_t cphi5 = {0xf, 0x1052df3, 0x0, 0x2c874f1, 0xa000, 0x59e669, 0x0, 0x1062863, 0x0, 0x459195};
static v2elm_t cphi6 = {0x18, 0x20a5be7, 0x0, 0x190e9e2, 0x12000, 0xb3ccd3, 0x0, 0x20c50c6, 0x0, 0xb232a};
static v2elm_t cphi7 = {0x23, 0x348781a, 0x0, 0x60c0d7, 0x18000, 0x2a1a66c, 0x0, 0x72678b, 0x0, 0x3963bc};
static v2elm_t cphi8 = {0xf0, 0x35d0ef0, 0x0, 0x94560a, 0xaa000, 0xbe544e, 0x0, 0x2180c5b, 0x0, 0x1f529f};
static v2elm_t cphi9 = {0xbef, 0x36e2505, 0x0, 0x34f9225, 0x870000, 0x375b014, 0x0, 0x273f800, 0x0, 0xfd52e};
static v2elm_t cpsi1 = {0x3e346ef, 0x13a, 0x1fd1d9, 0x0, 0xa02edf, 0xde000, 0x26a0f55, 0x0, 0x2af99e, 0x0};
static v2elm_t cpsi2 = {0x143, 0x203f372, 0x0, 0x37addc3, 0xe4000, 0x1f034c7, 0x0, 0x1ee66a0, 0x0, 0x21b8d0};
static v2elm_t cpsi3 = {0x9, 0x1e73a61, 0x0, 0x39aaf9d, 0x6000, 0x29063a6, 0x0, 0x5875f5, 0x0, 0x4cb26f};
static v2elm_t cpsi4 = {0x3fffff6, 0x218c59e, 0x3ffffff, 0x655062, 0x3ff9fff, 0x16f9c59, 0x3ffffff, 0x3a78a0a, 0x7fffff, 0x334d90};
// Fixed integer constants for the decomposition
// Close "offset" vector
static uint64_t c1 = {0x72482C5251A4559C};
static uint64_t c2 = {0x59F95B0ADD276F6C};
static uint64_t c3 = {0x7DD2D17C4625FA78};
static uint64_t c4 = {0x6BC57DEF56CE8877};
// Optimal basis vectors
static uint64_t b11 = {0x0906FF27E0A0A196};
static uint64_t b12 = {0x1363E862C22A2DA0};
static uint64_t b13 = {0x07426031ECC8030F};
static uint64_t b14 = {0x084F739986B9E651};
static uint64_t b21 = {0x1D495BEA84FCC2D4};
static uint64_t b24 = {0x25DBC5BC8DD167D0};
static uint64_t b31 = {0x17ABAD1D231F0302};
static uint64_t b32 = {0x02C4211AE388DA51};
static uint64_t b33 = {0x2E4D21C98927C49F};
static uint64_t b34 = {0x0A9E6F44C02ECD97};
static uint64_t b41 = {0x136E340A9108C83F};
static uint64_t b42 = {0x3122DF2DC3E0FF32};
static uint64_t b43 = {0x068A49F02AA8A9B5};
static uint64_t b44 = {0x18D5087896DE0AEA};
// Precomputed integers for fast-Babai rounding
static uint64_t ell1[4] = {0x259686E09D1A7D4F, 0xF75682ACE6A6BD66, 0xFC5BB5C5EA2BE5DF, 0x07};
static uint64_t ell2[4] = {0xD1BA1D84DD627AFB, 0x2BD235580F468D8D, 0x8FD4B04CAA6C0F8A, 0x03};
static uint64_t ell3[4] = {0x9B291A33678C203C, 0xC42BD6C965DCA902, 0xD038BF8D0BFFBAF6, 0x00};
static uint64_t ell4[4] = {0x12E5666B77E7FDC0, 0x81CBDC3714983D82, 0x1B073877A22D8410, 0x03};
/***********************************************/
/********** CURVE/SCALAR FUNCTIONS ***********/
static __inline void ecc_tau(vpoint_extproj_t P)
{ // Apply tau mapping to a point, P = tau(P)
// Input: P = (X1:Y1:Z1) on E in twisted Edwards coordinates
// Output: P = (Xfinal:Yfinal:Zfinal) on Ehat in twisted Edwards coordinates
v2elm_t t0, t1;
v2sqr1271(P->x, t0); // t0 = X1^2
v2sqr1271(P->y, t1); // t1 = Y1^2
v2mul1271(P->x, P->y, P->x); // X = X1*Y1
v2sqr1271(P->z, P->y); // Y = Z1^2
v2addsub1271(t1, t0, P->z, t0); // Z = X1^2+Y1^2, t0 = Y1^2-X1^2
v2mul1271(P->x, t0, P->x); // X = X1*Y1*(Y1^2-X1^2)
v2dblsub1271(P->y, t0, P->y); // Y = 2*Z1^2-(Y1^2-X1^2)
v2mul1271(P->x, ctau1, P->x); // Xfinal = X*ctau1
v2mul1271(P->y, P->z, P->y); // Yfinal = Y*Z
v2mul1271(P->z, t0, P->z); // Zfinal = t0*Z
}
static __inline void ecc_tau_dual(vpoint_extproj_t P)
{ // Apply tau_dual mapping to a point, P = tau_dual(P)
// Input: P = (X1:Y1:Z1) on Ehat in twisted Edwards coordinates
// Output: P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal) on E, where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
v2elm_t t0, t1, t2;
v2sqr1271(P->x, t0); // t0 = X1^2
v2sqr1271(P->z, t2); // t2 = Z1^2
v2sqr1271(P->y, t1); // t1 = Y1^2
v2addsub1271(t1, t0, t0, P->ta); // t0 = X1^2+Y1^2, Tafinal = Y1^2-X1^2
v2mul1271(P->x, P->y, P->x); // X = X1*Y1
v2dblsub1271(t2, P->ta, P->z); // Z = 2*Z1^2-(Y1^2-X1^2)
v2mul1271(P->x, ctaudual1, P->tb); // Tbfinal = ctaudual1*X1*X1
v2mul1271(P->z, P->ta, P->y); // Yfinal = Z*Tafinal
v2mul1271(P->tb, t0, P->x); // Xfinal = Tbfinal*t0
v2mul1271(P->z, t0, P->z); // Zfinal = Z*t0
}
static __inline void ecc_delphidel(vpoint_extproj_t P)
{ // Apply delta_phi_delta mapping to a point, P = delta(phi_W(delta_inv(P))),
// where phi_W is the endomorphism on the Weierstrass form.
// Input: P = (X1:Y1:Z1) on Ehat in twisted Edwards coordinates
// Output: P = (Xfinal:Yfinal:Zfinal) on Ehat in twisted Edwards coordinates
v2elm_t t0, t1, t2, t3, t4, t5, t6;
v2sqr1271(P->z, t4); // t4 = Z1^2
v2mul1271(P->y, P->z, t3); // t3 = Y1*Z1
v2mul1271(t4, cphi4, t0); // t0 = cphi4*t4
v2sqr1271(P->y, t2); // t2 = Y1^2
v2add1271(t0, t2, t0); // t0 = t0+t2
v2mul1271(t3, cphi3, t1); // t1 = cphi3*t3
v2addsub1271(t0, t1, t0, t5); // t0 = t0+t1, t5 = t0-t1
v2mul1271(t0, P->z, t0); // t0 = t0*Z1
v2mul1271(t3, cphi1, t1); // t1 = cphi1*t3
v2mul1271(t0, t5, t0); // t0 = t0*t5
v2mul1271(t4, cphi2, t5); // t5 = cphi2*t4
v2add1271(t2, t5, t5); // t5 = t2+t5
v2addsub1271(t1, t5, t1, t6); // t1 = t1+t5, t6 = t1-t5
v2mul1271(t6, t1, t6); // t6 = t1*t6
v2mul1271(t6, cphi0, t6); // t6 = cphi0*t6
v2mul1271(P->x, t6, P->x); // X = X1*t6
v2sqr1271(t2, t6); // t6 = t2^2
v2sqr1271(t3, t2); // t2 = t3^2
v2sqr1271(t4, t3); // t3 = t4^2
v2mul1271(t2, cphi8, t1); // t1 = cphi8*t2
v2mul1271(t3, cphi9, t5); // t5 = cphi9*t3
v2add1271(t1, t6, t1); // t1 = t1+t6
v2mul1271(t2, cphi6, t2); // t2 = cphi6*t2
v2mul1271(t3, cphi7, t3); // t3 = cphi7*t3
v2add1271(t1, t5, t1); // t1 = t1+t5
v2add1271(t2, t3, t2); // t2 = t2+t3
v2mul1271(t1, P->y, t1); // t1 = Y1*t1
v2add1271(t6, t2, P->y); // Y = t6+t2
v2mul1271(P->x, t1, P->x); // X = X*t1
v2mul1271(P->y, cphi5, P->y); // Y = cphi5*Y
v2neg1271_felm(P->x); // Xfinal = X^p
v2mul1271(P->y, P->z, P->y); // Y = Y*Z1
v2mul1271(t0, t1, P->z); // Z = t0*t1
v2mul1271(P->y, t0, P->y); // Y = Y*t0
v2neg1271_felm(P->z); // Zfinal = Z^p
v2neg1271_felm(P->y); // Yfinal = Y^p
}
static __inline void ecc_delpsidel(vpoint_extproj_t P)
{ // Apply delta_psi_delta mapping to a point, P = delta(psi_W(delta_inv(P))),
// where psi_W is the endomorphism on the Weierstrass form.
// Input: P = (X1:Y1:Z1) on Ehat in twisted Edwards coordinates
// Output: P = (Xfinal:Yfinal:Zfinal) on Ehat in twisted Edwards coordinates
v2elm_t t0, t1, t2;
v2neg1271_felm(P->x); // X = X1^p
v2neg1271_felm(P->z); // Z = Z1^p
v2neg1271_felm(P->y); // Y = Y1^p
v2sqr1271(P->z, t2); // t2 = Z1^p^2
v2sqr1271(P->x, t0); // t0 = X1^p^2
v2mul1271(P->x, t2, P->x); // X = X1^p*Z1^p^2
v2mul1271(t2, cpsi2, P->z); // Z = cpsi2*Z1^p^2
v2mul1271(t2, cpsi3, t1); // t1 = cpsi3*Z1^p^2
v2mul1271(t2, cpsi4, t2); // t2 = cpsi4*Z1^p^2
v2add1271(t0, P->z, P->z); // Z = X1^p^2 + cpsi2*Z1^p^2
v2add1271(t0, t2, t2); // t2 = X1^p^2 + cpsi4*Z1^p^2
v2add1271(t0, t1, t1); // t1 = X1^p^2 + cpsi3*Z1^p^2
v2neg1271(t2); // t2 = -(X1^p^2 + cpsi4*Z1^p^2)
v2mul1271(P->z, P->y, P->z); // Z = Y1^p*(X1^p^2 + cpsi2*Z1^p^2)
v2mul1271(P->x, t2, P->x); // X = -X1^p*Z1^p^2*(X1^p^2 + cpsi4*Z1^p^2)
v2mul1271(t1, P->z, P->y); // Yfinal = t1*Z
v2mul1271(P->x, cpsi1, P->x); // Xfinal = cpsi1*X
v2mul1271(P->z, t2, P->z); // Zfinal = Z*t2
}
void ecc_psi(vpoint_extproj_t P)
{ // Apply psi mapping to a point, P = psi(P)
// Input: P = (X1:Y1:Z1) on E in twisted Edwards coordinates
// Output: P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal) on E, where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
ecc_tau(P);
ecc_delpsidel(P);
ecc_tau_dual(P);
}
void ecc_phi(vpoint_extproj_t P)
{ // Apply phi mapping to a point, P = phi(P)
// Input: P = (X1:Y1:Z1) on E in twisted Edwards coordinates
// Output: P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal) on E, where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
ecc_tau(P);
ecc_delphidel(P);
ecc_tau_dual(P);
}
void ecc_precomp(vpoint_extproj_t P, vpoint_extproj_precomp_t *T)
{ // Generation of the precomputation table used by the variable-base scalar multiplication ecc_mul().
// Input: P = (X1,Y1,Z1,Ta,Tb), where T1 = Ta*Tb, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Output: table T containing 8 points: P, P+phi(P), P+psi(P), P+phi(P)+psi(P), P+psi(phi(P)), P+phi(P)+psi(phi(P)), P+psi(P)+psi(phi(P)), P+phi(P)+psi(P)+psi(phi(P))
// Precomputed points use the representation (X+Y,Y-X,2Z,2dT) corresponding to (X:Y:Z:T) in extended twisted Edwards coordinates
vpoint_extproj_precomp_t Q, R, S;
vpoint_extproj_t PP;
// Generating Q = phi(P) = (XQ+YQ,YQ-XQ,ZQ,TQ)
ecccopy(P, PP);
ecc_phi(PP);
R1_to_R3(PP, Q); // Converting from (X,Y,Z,Ta,Tb) to (X+Y,Y-X,Z,T)
// Generating S = psi(Q) = (XS+YS,YS-XS,ZS,TS)
ecc_psi(PP);
R1_to_R3(PP, S); // Converting from (X,Y,Z,Ta,Tb) to (X+Y,Y-X,Z,T)
// Generating T[0] = P = (XP+YP,YP-XP,2ZP,2dTP)
R1_to_R2(P, T[0]); // Converting from (X,Y,Z,Ta,Tb) to (X+Y,Y-X,2Z,2dT)
// Generating R = psi(P) = (XR+YR,YR-XR,ZR,TR)
ecc_psi(P);
R1_to_R3(P, R); // Converting from (X,Y,Z,Ta,Tb) to (X+Y,Y-X,Z,T)
eccadd_core(T[0], Q, PP); // T[1] = P+Q using the representations (X,Y,Z,Ta,Tb) <- (X+Y,Y-X,2Z,2dT) + (X+Y,Y-X,Z,T)
R1_to_R2(PP, T[1]); // Converting from (X,Y,Z,Ta,Tb) to (X+Y,Y-X,2Z,2dT)
eccadd_core(T[0], R, PP); // T[2] = P+R
R1_to_R2(PP, T[2]);
eccadd_core(T[1], R, PP); // T[3] = P+Q+R
R1_to_R2(PP, T[3]);
eccadd_core(T[0], S, PP); // T[4] = P+S
R1_to_R2(PP, T[4]);
eccadd_core(T[1], S, PP); // T[5] = P+Q+S
R1_to_R2(PP, T[5]);
eccadd_core(T[2], S, PP); // T[6] = P+R+S
R1_to_R2(PP, T[6]);
eccadd_core(T[3], S, PP); // T[7] = P+Q+R+S
R1_to_R2(PP, T[7]);
}
static __inline void mul_truncate(uint32_t* s, uint32_t* C, uint32_t* out)
{ // 256-bit multiplication with truncation for the scalar decomposition
// Outputs 64-bit value "out" = (uint64_t)((s * C) >> 256).
mul_truncate_a(s, C, out);
}
void decompose(uint64_t* k, uint64_t* scalars)
{ // Scalar decomposition for the variable-base scalar multiplication
// Input: scalar in the range [0, 2^256-1].
// Output: 4 64-bit sub-scalars.
uint64_t a1, a2, a3, a4, temp, mask;
mul_truncate_a((uint32_t*)k, (uint32_t*)ell1, (uint32_t*)&a1);
mul_truncate_a((uint32_t*)k, (uint32_t*)ell2, (uint32_t*)&a2);
mul_truncate_a((uint32_t*)k, (uint32_t*)ell3, (uint32_t*)&a3);
mul_truncate_a((uint32_t*)k, (uint32_t*)ell4, (uint32_t*)&a4);
temp = k[0] - (uint64_t)a1*b11 - (uint64_t)a2*b21 - (uint64_t)a3*b31 - (uint64_t)a4*b41 + c1;
mask = ~(0 - (temp & 1)); // If temp is even then mask = 0xFF...FF, else mask = 0
scalars[0] = temp + (mask & b41);
scalars[1] = (uint64_t)a1*b12 + (uint64_t)a2 - (uint64_t)a3*b32 - (uint64_t)a4*b42 + c2 + (mask & b42);
scalars[2] = (uint64_t)a3*b33 - (uint64_t)a1*b13 - (uint64_t)a2 + (uint64_t)a4*b43 + c3 - (mask & b43);
scalars[3] = (uint64_t)a1*b14 - (uint64_t)a2*b24 - (uint64_t)a3*b34 + (uint64_t)a4*b44 + c4 - (mask & b44);
}
void recode(uint64_t* scalars, unsigned int* digits, unsigned int* sign_masks)
{ // Recoding sub-scalars for use in the variable-base scalar multiplication. See Algorithm 1 in "Efficient and Secure Methods for GLV-Based Scalar
// Multiplication and their Implementation on GLV-GLS Curves (Extended Version)", A. Faz-Hernandez, P. Longa, and A.H. Sanchez, in Journal
// of Cryptographic Engineering, Vol. 5(1), 2015.
// Input: 4 64-bit sub-scalars passed through "scalars", which are obtained after calling decompose().
// Outputs: "digits" array with 65 nonzero entries. Each entry is in the range [0, 7], corresponding to one entry in the precomputed table.
// "sign_masks" array with 65 entries storing the signs for their corresponding digits in "digits".
// Notation: if the corresponding digit > 0 then sign_mask = 0xFF...FF, else if digit < 0 then sign_mask = 0.
unsigned int i, bit, bit0, carry;
sign_masks[64] = (unsigned int)-1;
for (i = 0; i < 64; i++)
{
scalars[0] >>= 1;
bit0 = (unsigned int)scalars[0] & 1;
sign_masks[i] = 0 - bit0;
bit = (unsigned int)scalars[1] & 1;
carry = (bit0 | bit) ^ bit0;
scalars[1] = (scalars[1] >> 1) + (uint64_t)carry;
digits[i] = bit;
bit = (unsigned int)scalars[2] & 1;
carry = (bit0 | bit) ^ bit0;
scalars[2] = (scalars[2] >> 1) + (uint64_t)carry;
digits[i] += (bit << 1);
bit = (unsigned int)scalars[3] & 1;
carry = (bit0 | bit) ^ bit0;
scalars[3] = (scalars[3] >> 1) + (uint64_t)carry;
digits[i] += (bit << 2);
}
digits[64] = (unsigned int)(scalars[1] + (scalars[2] << 1) + (scalars[3] << 2));
}
void cofactor_clearing(vpoint_extproj_t P)
{ // Co-factor clearing
// Input: P = (X1,Y1,Z1,Ta,Tb), where T1 = Ta*Tb, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates.
// Output: P = 392*P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal), where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
vpoint_extproj_precomp_t Q;
R1_to_R2(P, Q); // Converting from (X,Y,Z,Ta,Tb) to (X+Y,Y-X,2Z,2dT)
eccdouble(P); // P = 2*P using representations (X,Y,Z,Ta,Tb) <- 2*(X,Y,Z)
eccadd(Q, P); // P = P+Q using representations (X,Y,Z,Ta,Tb) <- (X,Y,Z,Ta,Tb) + (X+Y,Y-X,2Z,2dT)
eccdouble(P);
eccdouble(P);
eccdouble(P);
eccdouble(P);
eccadd(Q, P);
eccdouble(P);
eccdouble(P);
eccdouble(P);
}
bool ecc_mul(point_t P, digit_t* k, point_t Q, bool clear_cofactor)
{ // Variable-base scalar multiplication Q = k*P using a 4-dimensional decomposition
// Inputs: scalar "k" in [0, 2^256-1],
// point P = (x,y) in affine coordinates,
// clear_cofactor = 1 (TRUE) or 0 (FALSE) whether cofactor clearing is required or not, respectively.
// Output: Q = k*P in affine coordinates (x,y).
// This function performs point validation and (if selected) cofactor clearing.
vpoint_t A;
vpoint_extproj_t R;
vpoint_extproj_precomp_t S, Table[8];
uint64_t scalars[NWORDS64_ORDER];
unsigned int digits[65], sign_masks[65];
int i;
point_setup(P, R); // Convert to vectorized representation (X,Y,1,Ta,Tb)
if (ecc_point_validate(R) == false) { // Check if point lies on the curve
return false;
}
decompose((uint64_t*)k, scalars); // Scalar decomposition
if (clear_cofactor == true) {
cofactor_clearing(R);
}
recode(scalars, digits, sign_masks); // Scalar recoding
ecc_precomp(R, Table); // Precomputation
table_lookup_1x8(Table, S, digits[64], sign_masks[64]); // Extract initial point in (X+Y,Y-X,2Z,2dT) representation
R2_to_R4(S, R); // Conversion to representation (2X,2Y,2Z)
for (i = 63; i >= 0; i--)
{
table_lookup_1x8(Table, S, digits[i], sign_masks[i]); // Extract point S in (X+Y,Y-X,2Z,2dT) representation
eccdouble(R); // P = 2*P using representations (X,Y,Z,Ta,Tb) <- 2*(X,Y,Z)
eccadd(S, R); // P = P+S using representations (X,Y,Z,Ta,Tb) <- (X,Y,Z,Ta,Tb) + (X+Y,Y-X,2Z,2dT)
}
eccnorm(R, A); // Conversion to affine coordinates (x,y) and modular correction.
from_ext_to_std(A->x, Q->x);
from_ext_to_std(A->y, Q->y);
return true;
}
#endif
void eccset(point_t P)
{ // Set generator
// Output: P = (x,y)
fp2copy1271((felm_t*)&GENERATOR_x, P->x); // X1
fp2copy1271((felm_t*)&GENERATOR_y, P->y); // Y1
}
__inline void eccnorm(vpoint_extproj_t P, vpoint_t Q)
{ // Normalize a projective point (X1:Y1:Z1), including full reduction
// Input: P = (X1:Y1:Z1) in twisted Edwards coordinates
// Output: Q = (X1/Z1,Y1/Z1), corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
v2inv1271(P->z); // Z1 = Z1^-1
v2mul1271(P->x, P->z, Q->x); // X1 = X1/Z1
v2mul1271(P->y, P->z, Q->y); // Y1 = Y1/Z1
v2mod1271(Q->x, Q->x);
v2mod1271(Q->y, Q->y);
}
void R1_to_R2(vpoint_extproj_t P, vpoint_extproj_precomp_t Q)
{ // Conversion from representation (X,Y,Z,Ta,Tb) to (X+Y,Y-X,2Z,2dT), where T = Ta*Tb
// Input: P = (X1,Y1,Z1,Ta,Tb), where T1 = Ta*Tb, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Output: Q = (X1+Y1,Y1-X1,2Z1,2dT1) corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
v2add1271(P->ta, P->ta, Q->t2); // T = 2*Ta
v2add1271(P->x, P->y, Q->xy); // QX = X+Y
v2sub1271(P->y, P->x, Q->yx); // QY = Y-X
v2mul1271(Q->t2, P->tb, Q->t2); // T = 2*T
v2add1271(P->z, P->z, Q->z2); // QZ = 2*Z
v2mul1271(Q->t2, (digit_t*)&PARAMETER_d, Q->t2); // QT = 2d*T
}
void R1_to_R3(vpoint_extproj_t P, vpoint_extproj_precomp_t Q)
{ // Conversion from representation (X,Y,Z,Ta,Tb) to (X+Y,Y-X,Z,T), where T = Ta*Tb
// Input: P = (X1,Y1,Z1,Ta,Tb), where T1 = Ta*Tb, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Output: Q = (X1+Y1,Y1-X1,Z1,T1) corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
v2addsub1271(P->y, P->x, Q->xy, Q->yx); // XQ = (X1+Y1), YQ = (Y1-X1)
v2mul1271(P->ta, P->tb, Q->t2); // TQ = T1
v2copy1271(P->z, Q->z2); // ZQ = Z1
}
void R2_to_R4(vpoint_extproj_precomp_t P, vpoint_extproj_t Q)
{ // Conversion from representation (X+Y,Y-X,2Z,2dT) to (2X,2Y,2Z,2dT)
// Input: P = (X1+Y1,Y1-X1,2Z1,2dT1) corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Output: Q = (2X1,2Y1,2Z1) corresponding to (X1:Y1:Z1) in twisted Edwards coordinates
v2addsub1271(P->xy, P->yx, Q->y, Q->x); // YQ = 2*Y1, XQ = 2*X1
v2copy1271(P->z2, Q->z); // ZQ = 2*Z1
v2mod1271_incomplete(Q->x, Q->x);
v2mod1271_incomplete(Q->y, Q->y);
}
void eccdouble(vpoint_extproj_t P)
{ // Point doubling 2P
// Input: P = (X1:Y1:Z1) in twisted Edwards coordinates
// Output: 2P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal), where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
v2elm_t t1, t2;
#if !defined(MIX_ARM_NEON)
v2sqr1271(P->x, t1); // t1 = X1^2
v2sqr1271(P->y, t2); // t2 = Y1^2
v2add1271(P->x, P->y, P->x); // X = X1+Y1
v2addsub1271(t2, t1, P->tb, t1); // Tbfinal = X1^2+Y1^2, t1 = Y1^2-X1^2
v2sqr1271(P->z, t2); // t2 = Z1^2
v2sqr1271(P->x, P->ta); // Ta = (X1+Y1)^2
v2dblsub1271(t2, t1, t2); // t2 = 2Z1^2-(Y1^2-X1^2)
v2sub1271(P->ta, P->tb, P->ta); // Tafinal = 2X1*Y1 = (X1+Y1)^2-(X1^2+Y1^2)
v2mul1271(t1, P->tb, P->y); // Yfinal = (X1^2+Y1^2)(Y1^2-X1^2)
v2mul1271(t2, P->ta, P->x); // Xfinal = 2X1*Y1*[2Z1^2-(Y1^2-X1^2)]
v2mul1271(t1, t2, P->z); // Zfinal = (Y1^2-X1^2)[2Z1^2-(Y1^2-X1^2)]
#else
v2sqradd1271(P->x, t1, P->x, P->y, P->x); // t1 = X1^2, X = X1+Y1
v2sqr1271(P->y, t2); // t2 = Y1^2
v2sqraddsub1271(P->z, P->z, t2, t1, P->tb, t1); // Z = Z1^2, Tbfinal = X1^2+Y1^2, t1 = Y1^2-X1^2
v2sqr1271(P->x, P->ta); // Ta = (X1+Y1)^2
v2muldblsub1271(t1, P->tb, P->y, P->z, t1, t2); // Yfinal = (X1^2+Y1^2)(Y1^2-X1^2), t2 = 2Z1^2-(Y1^2-X1^2)
v2mulsub1271(t1, t2, P->z, P->ta, P->tb, P->ta); // Zfinal = (Y1^2-X1^2)[2Z1^2-(Y1^2-X1^2)], Tafinal = 2X1*Y1 = (X1+Y1)^2-(X1^2+Y1^2)
v2mul1271(t2, P->ta, P->x); // Xfinal = 2X1*Y1*[2Z1^2-(Y1^2-X1^2)]
#endif
}
__inline void eccadd_core(vpoint_extproj_precomp_t P, vpoint_extproj_precomp_t Q, vpoint_extproj_t R)
{ // Basic point addition R = P+Q or R = P+P
// Inputs: P = (X1+Y1,Y1-X1,2Z1,2dT1) corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Q = (X2+Y2,Y2-X2,Z2,T2) corresponding to (X2:Y2:Z2:T2) in extended twisted Edwards coordinates
// Output: R = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal), where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
v2elm_t t1, t2;
#if !defined(MIX_ARM_NEON)
v2mul1271(P->t2, Q->t2, R->z); // Z = 2dT1*T2
v2mul1271(P->z2, Q->z2, t1); // t1 = 2Z1*Z2
v2mul1271(P->xy, Q->xy, R->x); // X = (X1+Y1)(X2+Y2)
v2mul1271(P->yx, Q->yx, R->y); // Y = (Y1-X1)(Y2-X2)
v2addsub1271(R->x, R->y, R->ta, R->tb); // Tafinal = omega, Tbfinal = beta
v2addsub1271(t1, R->z, t1, t2); // t1 = alpha, t2 = theta
v2mul1271(R->tb, t2, R->x); // Xfinal = beta*theta
v2mul1271(t1, t2, R->z); // Zfinal = theta*alpha
v2mul1271(R->ta, t1, R->y); // Yfinal = alpha*omega
#else
v2mul1271(P->t2, Q->t2, R->z); // Z = 2dT1*T2
v2mul1271(P->z2, Q->z2, t1); // t1 = 2Z1*Z2
v2mul1271(P->xy, Q->xy, R->x); // X = (X1+Y1)(X2+Y2)
v2muladdsub1271(P->yx, Q->yx, R->y, t1, R->z, t1, t2); // Y = (Y1-X1)(Y2-X2), t1 = alpha, t2 = theta
v2muladdsub1271(t1, t2, R->z, R->x, R->y, R->ta, R->tb); // Zfinal = theta*alpha, Tafinal = omega, Tbfinal = beta
v2mul1271(t2, R->tb, R->x); // Xfinal = beta*theta
v2mul1271(t1, R->ta, R->y); // Yfinal = alpha*omega
#endif
}
void eccadd(vpoint_extproj_precomp_t Q, vpoint_extproj_t P)
{ // Complete point addition P = P+Q or P = P+P
// Inputs: P = (X1,Y1,Z1,Ta,Tb), where T1 = Ta*Tb, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Q = (X2+Y2,Y2-X2,2Z2,2dT2) corresponding to (X2:Y2:Z2:T2) in extended twisted Edwards coordinates
// Output: P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal), where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
#if !defined(MIX_ARM_NEON)
vpoint_precomp_t R;
v2elm_t t1;
v2addsub1271(P->y, P->x, R->xy, R->yx); // XR = (X1+Y1), YR = (Y1-X1)
v2mul1271(P->ta, P->tb, R->t2); // TR = T1
v2mul1271(Q->z2, P->z, t1); // t1 = 2Z1*Z2
v2mul1271(Q->t2, R->t2, P->z); // Z = 2dT1*T2
v2mul1271(Q->xy, R->xy, P->x); // X = (X1+Y1)(X2+Y2)
v2mul1271(Q->yx, R->yx, P->y); // Y = (Y1-X1)(Y2-X2)
v2addsub1271(P->x, P->y, P->ta, P->tb); // Tafinal = omega, Tbfinal = beta
v2addsub1271(t1, P->z, t1, R->t2); // t1 = alpha, TR = theta
v2mul1271(P->tb, R->t2, P->x); // Xfinal = beta*theta
v2mul1271(t1, R->t2, P->z); // Zfinal = theta*alpha
v2mul1271(P->ta, t1, P->y); // Yfinal = alpha*omega
#else
v2elm_t t1, t2;
v2muladdsub1271(P->ta, P->tb, P->ta, P->y, P->x, P->tb, P->y); // Ta = T1, Tb = (X1+Y1), Y = (Y1-X1)
v2mul1271(P->z, Q->z2, t1); // t1 = 2Z1*Z2
v2mul1271(P->ta, Q->t2, P->z); // Z = 2dT1*T2
v2muladdsub1271(P->tb, Q->xy, P->x, t1, P->z, t1, t2); // X = (X1+Y1)(X2+Y2), t1 = alpha, t2 = theta
v2mul1271(P->y, Q->yx, P->y); // Y = (Y1-X1)(Y2-X2)
v2muladdsub1271(t2, t1, P->z, P->x, P->y, P->ta, P->tb); // Zfinal = theta*alpha, Tafinal = omega, Tbfinal = beta
v2mul1271(t2, P->tb, P->x); // Xfinal = beta*theta
v2mul1271(t1, P->ta, P->y); // Yfinal = alpha*omega
#endif
}
void point_setup(point_t P, vpoint_extproj_t Q)
{ // Point conversion to vectorized representation (X,Y,Z,Ta,Tb)
// Input: P = (x,y) in affine coordinates
// Output: P = (X,Y,1,Ta,Tb), where Ta=X, Tb=Y and T=Ta*Tb, corresponding to (X:Y:Z:T) in extended twisted Edwards coordinates
from_std_to_ext(P->x, Q->x);
from_std_to_ext(P->y, Q->y);
v2copy1271(Q->x, Q->ta); // Ta = X1
v2copy1271(Q->y, Q->tb); // Tb = Y1
v2zero1271(Q->z); Q->z[0]=1; // Z1 = 1
}
bool ecc_point_validate(vpoint_extproj_t P)
{ // Point validation: check if point lies on the curve
// Input: P = (x,y) in affine coordinates, where x, y in [0, 2^127-1].
// Output: TRUE (1) if point lies on the curve E: -x^2+y^2-1-dx^2*y^2 = 0, FALSE (0) otherwise.
// SECURITY NOTE: this function does not run in constant time (input point P is assumed to be public).
v2elm_t t1, t2, t3;
unsigned int i;
v2sqr1271(P->y, t1);
v2sqr1271(P->x, t2);
v2sub1271(t1, t2, t3); // -x^2 + y^2
v2mul1271(t1, t2, t1); // x^2*y^2
v2mul1271((digit_t*)&PARAMETER_d, t1, t2); // dx^2*y^2
v2zero1271(t1); t1[0] = 1; // t1 = 1
v2add1271(t2, t1, t2); // 1 + dx^2*y^2
v2sub1271(t3, t2, t1); // -x^2 + y^2 - 1 - dx^2*y^2
v2mod1271(t1, t1);
for (i = 0; i < 2*VWORDS_FIELD-1; i++) {
if (t1[i] != 0) return false;
}
return true;
}
static __inline void R5_to_R1(vpoint_precomp_t P, vpoint_extproj_t Q)
{ // Conversion from representation (x+y,y-x,2dt) to (X,Y,Z,Ta,Tb)
// Input: P = (x1+y1,y1-x1,2dt1) corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates, where Z1=1
// Output: Q = (x1,y1,z1,x1,y1), where z1=1, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
v2addsub1271(P->xy, P->yx, Q->y, Q->x); // 2*y1, 2*x1
v2zero1271(Q->z); Q->z[0]=1; // ZQ = 1
v2div1271(Q->x); // XQ = x1
v2div1271(Q->y); // YQ = y1
v2copy1271(Q->x, Q->ta); // TaQ = x1
v2copy1271(Q->y, Q->tb); // TbQ = y1
}
static __inline void eccmadd(vpoint_precomp_t Q, vpoint_extproj_t P)
{ // Mixed point addition P = P+Q or P = P+P
// Inputs: P = (X1,Y1,Z1,Ta,Tb), where T1 = Ta*Tb, corresponding to (X1:Y1:Z1:T1) in extended twisted Edwards coordinates
// Q = (x2+y2,y2-x2,2dt2) corresponding to (X2:Y2:Z2:T2) in extended twisted Edwards coordinates, where Z2=1
// Output: P = (Xfinal,Yfinal,Zfinal,Tafinal,Tbfinal), where Tfinal = Tafinal*Tbfinal,
// corresponding to (Xfinal:Yfinal:Zfinal:Tfinal) in extended twisted Edwards coordinates
v2elm_t t1, t2;
#if !defined(MIX_ARM_NEON)
v2mul1271(P->ta, P->tb, P->ta); // Ta = T1
v2add1271(P->z, P->z, t1); // t1 = 2Z1
v2mul1271(P->ta, Q->t2, P->ta); // Ta = 2dT1*t2
v2addsub1271(P->y, P->x, P->z, P->tb); // Z = (X1+Y1), Tb = (Y1-X1)
v2addsub1271(t1, P->ta, t1, t2); // t1 = alpha, t2 = theta
v2mul1271(Q->xy, P->z, P->ta); // Ta = (X1+Y1)(x2+y2)
v2mul1271(Q->yx, P->tb, P->x); // X = (Y1-X1)(y2-x2)
v2addsub1271(P->ta, P->x, P->ta, P->tb); // Tafinal = omega, Tbfinal = beta
v2mul1271(t1, t2, P->z); // Zfinal = theta*alpha
v2mul1271(P->tb, t2, P->x); // Xfinal = beta*theta
v2mul1271(P->ta, t1, P->y); // Yfinal = alpha*omega
#else
v2muladd1271(P->ta, P->tb, P->ta, P->z, P->z, t1); // Ta = T1, t1 = 2Z1
v2muladdsub1271(P->ta, Q->t2, P->ta, P->y, P->x, P->z, P->tb); // Ta = 2dT1*t2, Z = (X1+Y1), Tb = (Y1-X1)
v2muladdsub1271(Q->xy, P->z, P->y, t1, P->ta, t1, t2); // Y = (X1+Y1)(x2+y2), t1 = alpha, t2 = theta
v2mul1271(Q->yx, P->tb, P->x); // X = (Y1-X1)(y2-x2)
v2muladdsub1271(t1, t2, P->z, P->y, P->x, P->ta, P->tb); // Zfinal = theta*alpha, Tafinal = omega, Tbfinal = beta
v2mul1271(P->tb, t2, P->x); // Xfinal = beta*theta
v2mul1271(P->ta, t1, P->y); // Yfinal = alpha*omega
#endif
}
bool ecc_mul_fixed(digit_t* k, point_t Q)
{ // Fixed-base scalar multiplication Q = k*G, where G is the generator. FIXED_BASE_TABLE stores v*2^(w-1) = 80 multiples of G.
// Inputs: scalar "k" in [0, 2^256-1].
// Output: Q = k*G in affine coordinates (x,y).
// The function is based on the modified LSB-set comb method, which converts the scalar to an odd signed representation
// with (bitlength(order)+w*v) digits.
unsigned int j, w = W_FIXEDBASE, v = V_FIXEDBASE, d = D_FIXEDBASE, e = E_FIXEDBASE;
unsigned int digit = 0, digits[NBITS_ORDER_PLUS_ONE+(W_FIXEDBASE*V_FIXEDBASE)-1] = {0};
digit_t temp[NWORDS_ORDER];
vpoint_t A;
vpoint_extproj_t R;
vpoint_precomp_t S;
int i, ii;
modulo_order(k, temp); // temp = k mod (order)
conversion_to_odd(temp, temp); // Converting scalar to odd using the prime subgroup order
mLSB_set_recode((uint64_t*)temp, digits); // Scalar recoding
// Extracting initial digit
digit = digits[w*d-1];
for (i = (int)((w-1)*d-1); i >= (int)(2*d-1); i = i-d)
{
digit = 2*digit + digits[i];
}
// Initialize R = (x+y,y-x,2dt) with a point from the table
table_lookup_fixed_base(((vpoint_precomp_t*)&FIXED_BASE_TABLE)+(v-1)*(1 << (w-1)), S, digit, digits[d-1]);
R5_to_R1(S, R); // Converting to representation (X:Y:1:Ta:Tb)
for (j = 0; j < (v-1); j++)
{
digit = digits[w*d-(j+1)*e-1];
for (i = (int)((w-1)*d-(j+1)*e-1); i >= (int)(2*d-(j+1)*e-1); i = i-d)
{
digit = 2*digit + digits[i];
}
// Extract point in (x+y,y-x,2dt) representation
table_lookup_fixed_base(((vpoint_precomp_t*)&FIXED_BASE_TABLE)+(v-j-2)*(1 << (w-1)), S, digit, digits[d-(j+1)*e-1]);
eccmadd(S, R); // R = R+S using representations (X,Y,Z,Ta,Tb) <- (X,Y,Z,Ta,Tb) + (x+y,y-x,2dt)
}
for (ii = (e-2); ii >= 0; ii--)
{
eccdouble(R); // R = 2*R using representations (X,Y,Z,Ta,Tb) <- 2*(X,Y,Z)
for (j = 0; j < v; j++)
{
digit = digits[w*d-j*e+ii-e];
for (i = (int)((w-1)*d-j*e+ii-e); i >= (int)(2*d-j*e+ii-e); i = i-d)
{
digit = 2*digit + digits[i];
}
// Extract point in (x+y,y-x,2dt) representation
table_lookup_fixed_base(((vpoint_precomp_t*)&FIXED_BASE_TABLE)+(v-j-1)*(1 << (w-1)), S, digit, digits[d-j*e+ii-e]);
eccmadd(S, R); // R = R+S using representations (X,Y,Z,Ta,Tb) <- (X,Y,Z,Ta,Tb) + (x+y,y-x,2dt)
}
}
eccnorm(R, A); // Conversion to affine coordinates (x,y) and modular correction.
from_ext_to_std(A->x, Q->x);
from_ext_to_std(A->y, Q->y);
return true;
}
void mLSB_set_recode(uint64_t* scalar, unsigned int *digits)
{ // Computes the modified LSB-set representation of a scalar
// Inputs: scalar in [0, order-1], where the order of FourQ's subgroup is 246 bits.
// Output: digits, where the first "d" values (from index 0 to (d-1)) store the signs for the recoded values using the convention: -1 (negative), 0 (positive), and
// the remaining values (from index d to (l-1)) store the recoded values in mLSB-set representation, excluding their sign,
// where l = d*w and d = ceil(bitlength(order)/(w*v))*v. The values v and w are fixed and must be in the range [1, 10] (see FourQ.h); they determine the size
// of the precomputed table "FIXED_BASE_TABLE" used by ecc_mul_fixed().
unsigned int i, j, d = D_FIXEDBASE, l = L_FIXEDBASE;
uint64_t temp, carry;
digits[d-1] = 0;
// Shift scalar to the right by 1
for (j = 0; j < (NWORDS64_ORDER-1); j++) {
SHIFTR(scalar[j+1], scalar[j], 1, scalar[j], RADIX64);
}
scalar[NWORDS64_ORDER-1] >>= 1;
for (i = 0; i < (d-1); i++)
{
digits[i] = (unsigned int)((scalar[0] & 1) - 1); // Convention for the "sign" row:
// if scalar_(i+1) = 0 then digit_i = -1 (negative), else if scalar_(i+1) = 1 then digit_i = 0 (positive)
// Shift scalar to the right by 1
for (j = 0; j < (NWORDS64_ORDER-1); j++) {
SHIFTR(scalar[j+1], scalar[j], 1, scalar[j], RADIX64);
}
scalar[NWORDS64_ORDER-1] >>= 1;
}
for (i = d; i < l; i++)
{
digits[i] = (unsigned int)(scalar[0] & 1); // digits_i = k mod 2. Sign is determined by the "sign" row
// Shift scalar to the right by 1
for (j = 0; j < (NWORDS64_ORDER-1); j++) {
SHIFTR(scalar[j+1], scalar[j], 1, scalar[j], RADIX64);
}
scalar[NWORDS64_ORDER-1] >>= 1;
temp = (0 - digits[i-(i/d)*d]) & digits[i]; // if (digits_i=0 \/ 1) then temp = 0, else if (digits_i=-1) then temp = 1
// floor(scalar/2) + temp
scalar[0] = scalar[0] + temp;
carry = (temp & (uint64_t)is_digit_zero_ct((digit_t)scalar[0])); // carry = (scalar[0] < temp);
for (j = 1; j < NWORDS64_ORDER; j++)
{
scalar[j] = scalar[j] + carry;
carry = (carry & (uint64_t)is_digit_zero_ct((digit_t)scalar[j])); // carry = (scalar[j] < temp);
}
}
return;
}
static __inline void eccneg_extproj_precomp(vpoint_extproj_precomp_t P, vpoint_extproj_precomp_t Q)
{ // Point negation
// Input : point P in coordinates (X+Y,Y-X,2Z,2dT)
// Output: point Q = -P = (Y-X,X+Y,2Z,-2dT)
v2copy1271(P->t2, Q->t2);
v2copy1271(P->xy, Q->yx);
v2copy1271(P->yx, Q->xy);
v2copy1271(P->z2, Q->z2);
v2neg1271(Q->t2);
}
static __inline void eccneg_precomp(vpoint_precomp_t P, vpoint_precomp_t Q)
{ // Point negation
// Input : point P in coordinates (x+y,y-x,2dt)
// Output: point Q = -P = (y-x,x+y,-2dt)
v2copy1271(P->t2, Q->t2);
v2copy1271(P->xy, Q->yx);
v2copy1271(P->yx, Q->xy);
v2neg1271(Q->t2);
}
bool ecc_mul_double(digit_t* k, point_t Q, digit_t* l, point_t R)
{ // Double scalar multiplication R = k*G + l*Q, where the G is the generator. Uses DOUBLE_SCALAR_TABLE, which contains multiples of G, Phi(G), Psi(G) and Phi(Psi(G)).
// Inputs: point Q in affine coordinates,
// Scalars "k" and "l" in [0, 2^256-1].
// Output: R = k*G + l*Q in affine coordinates (x,y).
// The function uses wNAF with interleaving.
vpoint_t A;
// SECURITY NOTE: this function is intended for a non-constant-time operation such as signature verification.
#if (USE_ENDO == true)
unsigned int position;
int i, digits_k1[65] = {0}, digits_k2[65] = {0}, digits_k3[65] = {0}, digits_k4[65] = {0};
int digits_l1[65] = {0}, digits_l2[65] = {0}, digits_l3[65] = {0}, digits_l4[65] = {0};
vpoint_precomp_t V;
vpoint_extproj_t Q1, Q2, Q3, Q4, T;
vpoint_extproj_precomp_t U, Q_table1[NPOINTS_DOUBLEMUL_WQ], Q_table2[NPOINTS_DOUBLEMUL_WQ], Q_table3[NPOINTS_DOUBLEMUL_WQ], Q_table4[NPOINTS_DOUBLEMUL_WQ];
uint64_t k_scalars[4], l_scalars[4];
point_setup(Q, Q1); // Convert to representation (X,Y,1,Ta,Tb)
if (ecc_point_validate(Q1) == false) { // Check if point lies on the curve
return false;
}
// Computing endomorphisms over point Q
ecccopy(Q1, Q2);
ecc_phi(Q2);
ecccopy(Q1, Q3);
ecc_psi(Q3);
ecccopy(Q2, Q4);
ecc_psi(Q4);
decompose((uint64_t*)k, k_scalars); // Scalar decomposition
decompose((uint64_t*)l, l_scalars);
wNAF_recode(k_scalars[0], WP_DOUBLEBASE, digits_k1); // Scalar recoding
wNAF_recode(k_scalars[1], WP_DOUBLEBASE, digits_k2);
wNAF_recode(k_scalars[2], WP_DOUBLEBASE, digits_k3);
wNAF_recode(k_scalars[3], WP_DOUBLEBASE, digits_k4);
wNAF_recode(l_scalars[0], WQ_DOUBLEBASE, digits_l1);
wNAF_recode(l_scalars[1], WQ_DOUBLEBASE, digits_l2);
wNAF_recode(l_scalars[2], WQ_DOUBLEBASE, digits_l3);
wNAF_recode(l_scalars[3], WQ_DOUBLEBASE, digits_l4);
ecc_precomp_double(Q1, Q_table1, NPOINTS_DOUBLEMUL_WQ); // Precomputation
ecc_precomp_double(Q2, Q_table2, NPOINTS_DOUBLEMUL_WQ);
ecc_precomp_double(Q3, Q_table3, NPOINTS_DOUBLEMUL_WQ);
ecc_precomp_double(Q4, Q_table4, NPOINTS_DOUBLEMUL_WQ);
v2zero1271(T->x); // Initialize T as the neutral point (0:1:1)
v2zero1271(T->y); T->y[0] = 1;
v2zero1271(T->z); T->z[0] = 1;
for (i = 64; i >= 0; i--)
{
eccdouble(T); // Double (X_T,Y_T,Z_T,Ta_T,Tb_T) = 2(X_T,Y_T,Z_T,Ta_T,Tb_T)
if (digits_l1[i] < 0) {
position = (-digits_l1[i])/2;
eccneg_extproj_precomp(Q_table1[position], U); // Load and negate U = (X_U,Y_U,Z_U,Td_U) <- -(X+Y,Y-X,2Z,2dT) from a point in the precomputed table
eccadd(U, T); // T = T+U = (X_T,Y_T,Z_T,Ta_T,Tb_T) = (X_T,Y_T,Z_T,Ta_T,Tb_T) + (X_U,Y_U,Z_U,Td_U)
} else if (digits_l1[i] > 0) {
position = (digits_l1[i])/2; // Take U = (X_U,Y_U,Z_U,Td_U) <- (X+Y,Y-X,2Z,2dT) from a point in the precomputed table
eccadd(Q_table1[position], T); // T = T+U = (X_T,Y_T,Z_T,Ta_T,Tb_T) = (X_T,Y_T,Z_T,Ta_T,Tb_T) + (X_U,Y_U,Z_U,Td_U)
}
if (digits_l2[i] < 0) {
position = (-digits_l2[i])/2;
eccneg_extproj_precomp(Q_table2[position], U);
eccadd(U, T);
} else if (digits_l2[i] > 0) {
position = (digits_l2[i])/2;
eccadd(Q_table2[position], T);
}
if (digits_l3[i] < 0) {
position = (-digits_l3[i])/2;
eccneg_extproj_precomp(Q_table3[position], U);
eccadd(U, T);
} else if (digits_l3[i] > 0) {
position = (digits_l3[i])/2;
eccadd(Q_table3[position], T);
}
if (digits_l4[i] < 0) {
position = (-digits_l4[i])/2;
eccneg_extproj_precomp(Q_table4[position], U);
eccadd(U, T);
} else if (digits_l4[i] > 0) {
position = (digits_l4[i])/2;
eccadd(Q_table4[position], T);
}
if (digits_k1[i] < 0) {
position = (-digits_k1[i])/2;
eccneg_precomp(((vpoint_precomp_t*)&DOUBLE_SCALAR_TABLE)[position], V); // Load and negate V = (X_V,Y_V,Z_V,Td_V) <- -(x+y,y-x,2dt) from a point in the precomputed table