1337UP Live CTF 2023

Decided to try some cryptography challenges on 1337UP LIVE CTF 2023 organised by Intigriti.

Really Secure Apparently

Apparently this encryption is “really secure” and I don’t need to worry about sharing the ciphertext, or even these values..

n = 689061037339483636851744871564868379980061151991904073814057216873412583484720768694905841053416938972235588548525570270575285633894975913717130070544407480547826227398039831409929129742007101671851757453656032161443946817685708282221883187089692065998793742064551244403369599965441075497085384181772038720949

e = 98161001623245946455371459972270637048947096740867123960987426843075734419854169415217693040603943985614577854750928453684840929755254248201161248375350238628917413291201125030514500977409961838501076015838508082749034318410808298025858181711613372870289482890074072555265382600388541381732534018133370862587

Author: CryptoCat

Downloadable File	SHA256 checksum
ciphertext	d7d7fc3befaf2696bc5de01a9f7e92d055a66ba2f10d22eb1ac4c1284310ff7f

Remove white space from hexdump of Ciphertext.

027401CA8188B58051F88ED8E4136762375D5D8DADF88FD1475D7E55125B379D25CC8D39DF7A56EBC0415BF1BF5D8A672A98E865B43CD9553AF6CF975AD9464755313D5309BB55F1DD307F9EB0C4A1AB3EABA4806D1F275230D53801BECD48238C45CF4FD9052C42776F5A79C0FE63C3AE7092DE1D26586209804AD6AB6F767FFC

Convert from Hexadecimal to Decimal. Reference: https://www.rapidtables.com/convert/number/hex-to-decimal.html

With the following variables:

N = 689061037339483636851744871564868379980061151991904073814057216873412583484720768694905841053416938972235588548525570270575285633894975913717130070544407480547826227398039831409929129742007101671851757453656032161443946817685708282221883187089692065998793742064551244403369599965441075497085384181772038720949

E = 98161001623245946455371459972270637048947096740867123960987426843075734419854169415217693040603943985614577854750928453684840929755254248201161248375350238628917413291201125030514500977409961838501076015838508082749034318410808298025858181711613372870289482890074072555265382600388541381732534018133370862587

C = 441001510077083440712098978980133930415086107290453312932779721137710693129669898774537962879522006041519477907847531444975796042514212299155087533072902229706427765901890350700252954929903001909850453303487994374982644931473474420223319182460327997419996588889034403777436157228265528747769729921745312710652

Solve RSA challenge. Reference: https://www.dcode.fr/rsa-cipher

Flag: INTIGRITI{0r_n07_50_53cur3_m4yb3}

Keyless

My friend made a new encryption algorithm. Apparently it’s so advanced, you don’t even need a key!

Author: CryptoCat

Downloadable File	SHA256 checksum
keyless.zip	e3f14512e804d092eb51467aad9e2e82f04fab7d754613a098e8a5dacce6da0d

Provided with encrypt.py and flag.txt.enc.

Used ChatGPT to produce python script with the following prompts.

Write a python script that implements the reverse process

Modify the script such that encrypted flag is supplied as 'flag.txt.enc'

UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 25: character maps to <undefined>

def decrypt(encrypted_message):
    decrypted_message = ""
    for char in encrypted_message:
        decrypted_char = ord(char) ^ 23
        c = decrypted_char + 7
        b = c // 3
        a = (b - 5) ^ 42
        original_char = (a - 10) // 2
        decrypted_message += chr(original_char)
    return decrypted_message
# Reading the encrypted flag from file using binary mode
with open("flag.txt.enc", "rb") as file:
    encrypted_flag = file.read().decode('utf-8').strip()
decrypted_flag = decrypt(encrypted_flag)
print("Decrypted Flag:", decrypted_flag)

Flag: INTIGRITI{m4yb3_4_k3y_w0uld_b3_b3773r_4f73r_4ll}

I am still trying to solve the following challenges. Appreciate a nudge in the correct direction!

Not So Smooth

Can you find a and b?

Author: ConnorM

Downloadable File	SHA256 checksum
notsosmooth.py	5b667b991f176eb3173f0d41a2993c679f822983b0d93fd1f84b0680b326f0c7

1-10

One equation, ten unknowns?

Author: ConnorM

Downloadable File	SHA256 checksum
one_equation.zip	621d798dfe4bea8fcc0440549c47031250d5c7aa4f5b53effe2bd76828265fa1