WindowsXPKg/util.cpp

82 lines
2.7 KiB
C++

//
// Created by Andrew on 01/06/2023.
//
#include "header.h"
/* Convert data between endianness types. */
void endian(byte *data, int length) {
for (int i = 0; i < length / 2; i++) {
byte temp = data[i];
data[i] = data[length - i - 1];
data[length - i - 1] = temp;
}
}
/* Initializes the elliptic curve. */
EC_GROUP *initializeEllipticCurve(
const char *pSel,
const char *aSel,
const char *bSel,
const char *generatorXSel,
const char *generatorYSel,
const char *publicKeyXSel,
const char *publicKeyYSel,
EC_POINT **genPoint,
EC_POINT **pubPoint
) {
// Initialize BIGNUM and BIGNUMCTX structures.
// BIGNUM - Large numbers
// BIGNUMCTX - Context large numbers (temporary)
BIGNUM *a, *b, *p, *generatorX, *generatorY, *publicKeyX, *publicKeyY;
BN_CTX *context;
// We're presented with an elliptic curve, a multivariable function y(x; p; a; b), where
// y^2 % p = x^3 + ax + b % p.
a = BN_new();
b = BN_new();
p = BN_new();
// Public key will consist of the resulting (x; y) values.
publicKeyX = BN_new();
publicKeyY = BN_new();
// G(x; y) is a generator function, its return value represents a point on the elliptic curve.
generatorX = BN_new();
generatorY = BN_new();
// Context variable
context = BN_CTX_new();
/* Public data */
BN_dec2bn(&p, pSel);
BN_dec2bn(&a, aSel);
BN_dec2bn(&b, bSel);
BN_dec2bn(&generatorX, generatorXSel);
BN_dec2bn(&generatorY, generatorYSel);
BN_dec2bn(&publicKeyX, publicKeyXSel);
BN_dec2bn(&publicKeyY, publicKeyYSel);
/* Elliptic Curve calculations. */
// The group is defined via Fp = all integers [0; p - 1], where p is prime.
// The function EC_POINT_set_affine_coordinates() sets the x and y coordinates for the point p defined over the curve given in group.
EC_GROUP *eCurve = EC_GROUP_new_curve_GFp(p, a, b, context);
// Create new point for the generator on the elliptic curve and set its coordinates to (genX; genY).
*genPoint = EC_POINT_new(eCurve);
EC_POINT_set_affine_coordinates(eCurve, *genPoint, generatorX, generatorY, context);
// Create new point for the public key on the elliptic curve and set its coordinates to (pubX; pubY).
*pubPoint = EC_POINT_new(eCurve);
EC_POINT_set_affine_coordinates(eCurve, *pubPoint, publicKeyX, publicKeyY, context);
// If generator and public key points are not on the elliptic curve, either the generator or the public key values are incorrect.
assert(EC_POINT_is_on_curve(eCurve, *genPoint, context) == 1);
assert(EC_POINT_is_on_curve(eCurve, *pubPoint, context) == 1);
// Cleanup
BN_CTX_free(context);
return eCurve;
}