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October 15, 2017 18:26
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# Solution to SquareCTF "Seventeen" | |
# echo -ne "sandflea\n\x00" | python 17.py | |
import re | |
import sys | |
def parse(data): | |
labels = {} | |
instructions = [] | |
data = re.sub(r"/\*[^/]*?\*/", "", data.lower()) | |
lines = data.split("\n") | |
for line in lines: | |
line = line.strip().split(":") | |
if len(line) == 1: | |
instruction = line[0] | |
else: | |
assert(len(line) == 2) | |
label, instruction = line | |
labels[label] = len(instructions) | |
if instruction: | |
instructions += instruction.strip().split(" ") | |
return instructions, labels | |
def evaluate(word): | |
assert(word not in opcodes) | |
if type(word) is int: | |
return word | |
assert(type(word) is str) | |
if word in labels: | |
return labels[word] | |
elif word in variables: | |
return variables[word] | |
elif word.isdigit(): | |
return int(word) | |
else: | |
exit("Unable to evaluate: {}".format(word)) | |
def getarg(): | |
assert(stack) | |
return evaluate(stack.pop()) | |
opcodes = [ | |
"read_num", | |
"read_byte", | |
"add", | |
"sub", | |
"mod", | |
"store", | |
"xor", | |
"call", | |
"jump", | |
"vstore", | |
"vload", | |
"ifz", | |
"ifg", | |
"dup", | |
"print_byte", | |
"print_num", | |
"exit", | |
] | |
stack = [] | |
vector = {} # vector is implemented as a dict | |
variables = {} | |
lastvar = None | |
pc = 0 | |
instructions, labels = parse(open("passmgr.17", "r").read()) | |
running = True | |
while running: | |
inst = instructions[pc] | |
#print(stack, repr(inst)) | |
if inst in opcodes: | |
if inst == "read_num": | |
stack.append(int(input("NUM: "))) | |
elif inst == "read_byte": | |
#print(vector) | |
stack.append(sys.stdin.buffer.read(1)[0]) | |
elif inst == "print_byte": | |
sys.stdout.buffer.write(bytes([getarg()])) | |
elif inst == "print_num": | |
sys.stdout.buffer.write(str(getarg()).encode()) | |
elif inst == "add": | |
a = getarg() | |
b = getarg() | |
stack.append(a+b) | |
elif inst == "sub": | |
a = getarg() | |
b = getarg() | |
stack.append(b-a) | |
elif inst == "mod": | |
a = getarg() | |
b = getarg() | |
stack.append(b%a) | |
elif inst == "xor": | |
a = getarg() | |
b = getarg() | |
stack.append(b^a) | |
elif inst == "dup": | |
stack.append(stack[-1]) | |
elif inst == "store": | |
varname = stack.pop() # ignore... | |
varval = getarg() | |
variables[lastvar] = varval | |
elif inst == "vstore": | |
vecval = getarg() | |
idx = getarg() | |
vector[idx] = vecval | |
elif inst == "vload": | |
stack.append(vector.get(getarg(), 0)) | |
elif inst == "ifz": | |
la = getarg() | |
lb = getarg() | |
val = getarg() | |
if (val == 0): | |
pc = lb | |
else: | |
pc = la | |
continue # skip pc increment | |
elif inst == "ifg": | |
la = getarg() | |
lb = getarg() | |
val = getarg() | |
#a = getarg() | |
if (val > 0): | |
pc = lb | |
else: | |
pc = la | |
continue # skip pc increment | |
elif inst == "call": | |
newpc = getarg() | |
stack.append(pc+1) | |
pc = newpc | |
continue # skip pc increment | |
elif inst == "jump": | |
pc = getarg() | |
continue # skip pc increment | |
elif inst == "exit": | |
exit() # clean exit | |
else: | |
exit("UNIMPLEMENTED: " + inst) | |
else: | |
if inst not in labels and not inst.isdigit(): | |
lastvar = inst | |
#if inst not in variables: | |
# print(inst) | |
stack.append(variables.get(inst, 0)) # default 0 ? | |
else: | |
stack.append(inst) | |
pc += 1 |
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