标签: Python

base92 | ISCTF2024 | Crypto ChaCha20-Poly1305

原题

from Crypto.Cipher import ChaCha20_Poly1305
import os

key = os.urandom(32)
nonce = os.urandom(12)

with open('flag.txt', 'rb') as f:
    plaintext = f.read()

cipher = ChaCha20_Poly1305.new(key=key, nonce=nonce)

ct, tag = cipher.encrypt_and_digest(plaintext)

print(f"Encrypted Flag: {ct.hex()}")
print(f"Tag: {tag.hex()}")
print(f"Nonce: {nonce.hex()}")

with open('key.txt', 'w') as key_file:
    key_file.write(key.hex())

undefined2024/12/10大约 1 分钟

费马函数 | ISCTF2024 | Crypto 蓝鲨的费马

原题

import libnum
import gmpy2
from Crypto.Util.number import *

flag=b'ISCTF{********}'
m=bytes_to_long(flag)

p=libnum.generate_prime(1024)
q=libnum.generate_prime(1024)
n=p*q
e=0x10001
c=pow(m,e,n)
d=inverse(e,(p-1)*(q-1))
leak = (d+(pow(p,q,n)+pow(q,p,n)))%n

print("c=", c)
print("n=", n)
print("leak=", leak)

"""
c= 8989289659072309605793417141528767265266446236550650613514493589798432446586991233583435051268377555448062724563967695425657559568596372723980081067589103919296476501677424322525079257328042851349095575718347302884996529329066703597604694781627113384086536158793653551546025090807063130353950841148535682974762381044510423210397947080397718080033363000599995100765708244828566873128882878164321817156170983773105693537799111546309755235573342169431295776881832991533489235535981382958295960435126843833532716436804949502318851112378495533302256759494573250596802016112398817816155228378089079806308296705261876583997
n= 13424018200035368603483071894166480724482952594135293395398366121467209427078817227870501294732149372214083432516059795712917132804111155585926502759533393295089100965059106772393520277313184519450478832376508528256865861027444446718552169503579478134286009893965458507369983396982525906466073384013443851551139147777507283791250268462136554061959016630318688169168797939873600493494258467352326974238472394214986505312411729432927489878418792288365594455065912126527908319239444514857325441614280498882524432151918146061570116187524918358453036228204087993064505391742062288050068745930452767100091519798860487150247
leak= 9192002086528025412361053058922669469031188193149143635074798633855112230489479254740324032262690315813650428270911079121913869290893574897752990491429582640499542165616254566396564016734157323265631446079744216458719690853526969359930225042993006404843355356540487296896949431969541367144841985153231095140361069256753593550199420993461786814074270171257117410848796614931926182811404655619662690700351986753661502438299236428991412206196135090756862851230228396476709412020941670878645924203989895008014836619321109848938770269989596541278600166088022166386213646074764712810133558692545401032391239330088256431881
"""

undefined2024/12/10小于 1 分钟

Python搜索算法 | ISCTF2024 | Reverse《回忆安魂曲》--第三章：逃不出的黑墙

将文件拖入 IDA 分析可得以下内容

可以从中提取出迷宫的字符串。

undefined2024/12/10大约 2 分钟

RSA | ISCTF2024 | Crypto 我和小蓝鲨的秘密

原题

from PIL import Image
from Crypto.Util.number import bytes_to_long, long_to_bytes
import numpy as np

n = 29869349657224745144762606999
e = 65537

original_image_path = "flag.jpg"
img = Image.open(original_image_path)
img = img.convert("RGB")

img_array = np.array(img)
h, w, _ = img_array.shape

encrypted_array = np.zeros((h, w, 3), dtype=object)
for i in range(h):
    for j in range(w):
        r, g, b = int(img_array[i, j, 0]), int(img_array[i, j, 1]), int(img_array[i, j, 2])

        encrypted_array[i, j, 0] = pow(r, e, n)
        encrypted_array[i, j, 1] = pow(g, e, n)
        encrypted_array[i, j, 2] = pow(b, e, n)

np.save("encrypted_image.npy", encrypted_array)
print("图片已加密并保存为 encrypted_image.npy")

undefined2024/12/10大约 2 分钟

session伪造 Python反序列化远程Shell | ISCTF2024 | Web 新闻系统

分析代码，

@app.route("/login", methods=["GET", "POST"])
def login():
    if request.method == "POST":
        username = request.form.get('username')
        password = request.form.get('password')
        if username == 'test' and password == 'test111':
            session['username'] = username
            session['password'] = password
            session['status'] = 'user'
            return redirect('/news')
        else:
            session['login_error'] = True
    return render_template("login.html")

undefined2024/12/10大约 2 分钟

椭圆曲线签名算法 | 网鼎杯20241029青龙组 | Crypto2

原题

import gmpy2
import random
import binascii
from hashlib import sha256
from sympy import nextprime
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad
from Crypto.Util.number import long_to_bytes
from FLAG import flag
#flag = 'wdflag{123}'

def victory_encrypt(plaintext, key):
    key = key.upper()
    key_length = len(key)
    plaintext = plaintext.upper()
    ciphertext = ''

    for i, char in enumerate(plaintext):
        if char.isalpha():
            shift = ord(key[i % key_length]) - ord('A')
            encrypted_char = chr((ord(char) - ord('A') + shift) % 26 + ord('A'))
            ciphertext += encrypted_char
        else:
            ciphertext += char

    return ciphertext

victory_key = "WANGDINGCUP"
victory_encrypted_flag = victory_encrypt(flag, victory_key)

p = 0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f
a = 0
b = 7
xG = 0x79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798
yG = 0x483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8
G = (xG, yG)
n = 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
h = 1
zero = (0,0)

dA = nextprime(random.randint(0, n))

if dA > n:
    print("warning!!")

def addition(t1, t2):
    if t1 == zero:
        return t2
    if t2 == zero:
        return t2
    (m1, n1) = t1
    (m2, n2) = t2
    if m1 == m2:
        if n1 == 0 or n1 != n2:
            return zero
        else:
            k = (3 * m1 * m1 + a) % p * gmpy2.invert(2 * n1 , p) % p
    else:
        k = (n2 - n1 + p) % p * gmpy2.invert((m2 - m1 + p) % p, p) % p
    m3 = (k * k % p - m1 - m2 + p * 2) % p
    n3 = (k * (m1 - m3) % p - n1 + p) % p
    return (int(m3),int(n3))

def multiplication(x, k):
    ans = zero
    t = 1
    while(t <= k):
        if (k &t )>0:
            ans = addition(ans, x)
        x = addition(x, x)
        t <<= 1
    return ans

def getrs(z, k):
    (xp, yp) = P
    r = xp
    s = (z + r * dA % n) % n * gmpy2.invert(k, n) % n
    return r,s

z1 = random.randint(0, p)
z2 = random.randint(0, p)
k = random.randint(0, n)
P = multiplication(G, k)
hA = multiplication(G, dA)
r1, s1 = getrs(z1, k)
r2, s2 = getrs(z2, k)

print("r1 = {}".format(r1))
print("r2 = {}".format(r2))
print("s1 = {}".format(s1))
print("s2 = {}".format(s2))
print("z1 = {}".format(z1))
print("z2 = {}".format(z2))

key = sha256(long_to_bytes(dA)).digest()
cipher = AES.new(key, AES.MODE_CBC)
iv = cipher.iv
encrypted_flag = cipher.encrypt(pad(victory_encrypted_flag.encode(), AES.block_size))
encrypted_flag_hex = binascii.hexlify(iv + encrypted_flag).decode('utf-8')

print("Encrypted flag (AES in CBC mode, hex):", encrypted_flag_hex)

# output
# r1 = 86806104739558095745988469033305523200538774705708894815836887970976487278764
# r2 = 86806104739558095745988469033305523200538774705708894815836887970976487278764
# s1 = 93400851884262731807098055393482657423555590196362184363643455285862566867372
# s2 = 58741027521216057788923508334695668250013849866589902683641825341545919891746
# z1 = 47591695289461307212638536234394543297527537576682980326526736956079807805586
# z2 = 97911075901954715147720917205165523174582665086645698292621371632896283314804
# ('Encrypted flag (AES in CBC mode, hex):', u'86cd24e2914c0c4d9b87bea34005a98bd8587d14cae71909b917679d3328304e7915e6ba4cad1096faa4a85bc52f8056d3f21ef09516be8a5160f1b338a6b936')