Tags: cryptography
Rating:
```
import random
# Set the seed to match the original script
random.seed(1337)
# Define the original operations
ops = [
lambda x: x + 3,
lambda x: x - 3,
lambda x: x * 3,
lambda x: x ^ 3,
]
# Define the reverse operations
reverse_ops = [
lambda x: x - 3,
lambda x: x + 3,
lambda x: x // 3 if x % 3 == 0 else None, # x // 3 with an additional check
lambda x: x ^ 3,
]
# The 'out' list from the challenge
out = [354, 112, 297, 119, 306, 369, 111, 108, 333, 110, 112, 92, 111, 315, 104, 102, 285, 102, 303, 100, 112, 94, 111, 285, 97, 351, 113, 98, 108, 118, 109, 119, 98, 94, 51, 56, 159, 50, 53, 153, 100, 144, 98, 51, 53, 303, 99, 52, 49, 128]
# List to store the recovered flag bytes
flag = []
# Iterate over the output and reverse the applied operations
for v in out:
op_index = random.randint(0, 3) # Get the index of the operation applied
reverse_op = reverse_ops[op_index] # Get the corresponding reverse operation
reversed_value = reverse_op(v) # Apply the reverse operation
# Check if reverse operation was valid
if reversed_value is not None:
flag.append(reversed_value)
else:
print(f"Failed to reverse operation for value {v} with operation index {op_index}")
flag.append(ord('?')) # Use '?' for unknown characters
# Convert the flag list back to bytes and decode, replacing invalid bytes with '?'
flag_bytes = bytes(flag)
print(flag_bytes.decode('utf-8', 'replace'))
```
