Crypto Yors Truly

I have encrypted some text but it seems I have lost the key! Can you find it?

We’re provided a Python source file:

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import base64
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plaintext = "A string of text can be encrypted by applying the bitwise XOR operator to every character using a given key"
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key = "" # I have lost the key!
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def byte_xor(ba1, ba2):
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    return bytes([_a ^ _b for _a, _b in zip(ba1, ba2)])
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ciphertext_b64 = base64.b64encode(byte_xor(key.encode(), plaintext.encode()))
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ciphertext_decoded = base64.b64decode("NkMHEgkxXjV/BlN/ElUKMVZQEzFtGzpsVTgGDw==")
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print(ciphertext_decoded)

Note that XOR is a reversible operation, since a ^ a = 0 and XOR is associative and commutative.

Therefore, to recover the key, it we can simply XOR the plaintet and the ciphertext. See below:

$plaintext=pt$
$ciphertext=ct$
$ct=pt \oplus key$
$ct \oplus pt = pt \oplus key \oplus pt = key$

Therefore, here is the solve script:

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import base64
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plaintext = "A string of text can be encrypted by applying the bitwise XOR operator to every character using a given key"
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key = "" # I have lost the key!
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def byte_xor(ba1, ba2):
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    return bytes([_a ^ _b for _a, _b in zip(ba1, ba2)])
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ciphertext_b64 = base64.b64encode(byte_xor(key.encode(), plaintext.encode()))
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ciphertext_decoded = base64.b64decode("NkMHEgkxXjV/BlN/ElUKMVZQEzFtGzpsVTgGDw==")
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print(byte_xor(plaintext.encode(), ciphertext_decoded))

Run the script to get the flag!

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wctf{X0R_i5_f0rEv3r_My_L0Ve}