computeAES.md

computeAES

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Question

You found this clue laying around. Can you decrypt it?

HINTS

Try online tools or python

File contents

Encrypted with AES in ECB mode. All values base64 encoded
ciphertext = I300ryGVTXJVT803Sdt/KcOGlyPStZkeIHKapRjzwWf9+p7fIWkBnCWu/IWls+5S
key = iyq1bFDkirtGqiFz7OVi4A==

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Solution

The ciphertext is encrypted using AES ECB and then base64 encoded. Key is also base64 encoded. You can do it using Python Packages like pycrypto. But I used OPENSSL command line tool.

Steps:

1. First decode the key from base64 to hex.

Key in base64 : iyq1bFDkirtGqiFz7OVi4A==
Key in Hex : 8B2AB56C50E48ABB46AA2173ECE562E0

2. Then copy the ciphertext to a file and run the following openssl command.

openssl enc -d -aes-128-ecb -in aesecbcipher.txt -out aesecbplain.txt -nopad -nosalt -K 8B2AB56C50E48ABB46AA2173ECE562E0 -iv 0 -base64

3. cat the aesecbplain.txt file.

cat aesecbplain.txt
flag{do_not_let_machines_win_2d4975bc}__________

Tools

OpenSSL

base64 - Hex

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Thanks

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Github : @iammrdollar