WindowsXPKg/src/util.cpp

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//
// Created by Andrew on 01/06/2023.
//
#include "header.h"
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int randomRange() {
return 4; // chosen by fair dice roll
// guaranteed to be random
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}
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/* Convert data between endianness types. */
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void endian(BYTE *data, int length) {
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for (int i = 0; i < length / 2; i++) {
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BYTE temp = data[i];
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data[i] = data[length - i - 1];
data[length - i - 1] = temp;
}
}
/* Initializes the elliptic curve. */
EC_GROUP *initializeEllipticCurve(
const std::string pSel,
const std::string aSel,
const std::string bSel,
const std::string generatorXSel,
const std::string generatorYSel,
const std::string publicKeyXSel,
const std::string publicKeyYSel,
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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.c_str());
BN_dec2bn(&a, aSel.c_str());
BN_dec2bn(&b, bSel.c_str());
BN_dec2bn(&generatorX, generatorXSel.c_str());
BN_dec2bn(&generatorY, generatorYSel.c_str());
BN_dec2bn(&publicKeyX, publicKeyXSel.c_str());
BN_dec2bn(&publicKeyY, publicKeyYSel.c_str());
/* 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).
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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).
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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.
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assert(EC_POINT_is_on_curve(eCurve, genPoint, context) == true);
assert(EC_POINT_is_on_curve(eCurve, pubPoint, context) == true);
// Cleanup
BN_CTX_free(context);
return eCurve;
}
int BN_bn2lebin(const BIGNUM *a, unsigned char *to, int tolen) {
if (a == nullptr || to == nullptr)
return 0;
int len = BN_bn2bin(a, to);
if (len > tolen)
return -1;
// Choke point inside BN_bn2lebinpad: OpenSSL uses len instead of tolen.
endian(to, tolen);
return len;
}