Deterministic

CHALLENGE DESCRIPTION

There is a locked door in front of us that can only be opened with the secret passphrase. There are no keys anywhere in the room, only this .txt. There is also a writing on the wall.. State 0: 69420, State N: 999, flag ends at state N, key length: one.. Can you figure it out and open the door?

SOLUTION

We need to find the path from the beginning state to the end state.

from collections import defaultdict, deque

# Set start and end states
start_state = 69420
end_state = 999

# Build the graph
graph = defaultdict(list)

# Open and parse the file
with open('deterministic.txt', 'r') as f:
    for line in f:
        parts = line.strip().split()
        if len(parts) == 3:
            current_state = int(parts[0])
            input_char = parts[1]
            next_state = int(parts[2])
            graph[current_state].append((input_char, next_state))

# BFS to find the path
def bfs(start, end):
    queue = deque()
    queue.append((start, []))  # (current_state, path_so_far)
    visited = set()

    while queue:
        current_state, path = queue.popleft()
        if current_state in visited:
            continue
        visited.add(current_state)

        if current_state == end:
            return path

        for input_char, next_state in graph.get(current_state, []):
            queue.append((next_state, path + [input_char]))
    return None

# Find the path
path = bfs(start_state, end_state)

if path:
    flag = ' '.join(path)
    print("Output:", flag)
else:
    print("No path found from start to end.")

Now we have the output, copy the output to CyberChef, convert from Decimal to Ascii

We know the special key, now XOR it and we get the flag.