Cryptography 250: caesar cipher 2

Challenge

Can you help us decrypt this message? We believe it is a form of a caesar cipher.

You can find the ciphertext in /problems/caesar-cipher-2_3_4a1aa2a4d0f79a1f8e9a29319250740a on the shell server.

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4-'3evh?'c)7%t#e-r,g6u#.9uv#%tg2v#7g'w6gA

Solution

Looks like caesar shift cipher but with a larger alphabet. Since we know the flag
format, we can deduce the shift amount (e.g. 4 should become p). The most likely candidate is the ascii table

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import string

alphabet=""

for i in range(32,126):
    alphabet += chr(i)

print(alphabet)

shift=alphabet.find('p')-alphabet.find('4')
print(shift)

ct="4-'3evh?'c)7%t#e-r,g6u#.9uv#%tg2v#7g'w6gA"

pt=''
for c in ct:
    pt += alphabet[ (alphabet.find(c)+shift)%len(alphabet) ]

print(pt)

And this outputs the flag for us

Flag