Generate seednt16, original research by doegox

seednt16.c

#include <stdbool.h>
#include <assert.h>
#include <stdio.h>

static uint16_t prev_lfsr16(uint16_t x) {
    return ((x << 1 | x >> 15) & 0xffff) ^ ((x >> 1 ^ x >> 2 ^ x >> 4) & 0x100);
}

static uint16_t compute_seednt16_nt32(uint32_t nt32, uint64_t key) {
    static const uint8_t a[] = {0, 8, 9, 4, 6, 11, 1, 15, 12, 5, 2, 13, 10, 14, 3, 7};
    static const uint8_t b[] = {0, 13, 1, 14, 4, 10, 15, 7, 5, 3, 8, 6, 9, 2, 12, 11};
    uint16_t nt = nt32 >> 16;

    for (int i = 0; i < 14; i++) {
        nt = prev_lfsr16(nt);
    }

    bool odd = true;
    for (int i = 0; i < 6 * 8; i += 8) {
        if (odd) {
            nt ^= a[(key >> i) & 0xF] | (b[(key >> (i + 4)) & 0xF] << 4);
        } else {
            nt ^= b[(key >> i) & 0xF] | (a[(key >> (i + 4)) & 0xF] << 4);
        }
        odd = !odd;
        for (int j = 0; j < 8 + i / 8; j++) {
            nt = prev_lfsr16(nt);
        }
    }
    return nt;
}


int main() {
    // Test compute_seednt16_nt32
    uint32_t nt32 = 0x12345678;
    uint64_t key = 0x0123456789AB;
    uint16_t result = compute_seednt16_nt32(nt32, key);
    printf("compute_seednt16_nt32 result: 0x%04X\n", result);
    return 0;
}