# Level 7: AES in ECB mode
## Task
The Base64-encoded content [in this file](https://cryptopals.com/static/challenge-data/7.txt) has been encrypted via AES-128 in ECB mode under the key
```
"YELLOW SUBMARINE".
```
(case-sensitive, without the quotes; exactly 16 characters; I like "YELLOW SUBMARINE" because it's exactly 16 bytes long, and now you do too).
Decrypt it. You know the key, after all.
Easiest way: use OpenSSL::Cipher and give it AES-128-ECB as the cipher.
{% hint style="warning" %}
#### Do this with code.
You can obviously decrypt this using the OpenSSL command-line tool, but we're having you get ECB working in code for a reason. You'll need it *a lot* later on, and not just for attacking ECB.
{% endhint %}
***
### Explanation
**What is AES?**
AES (Advanced Encryption Standard) is a symmetric cipher algorithm that operates on 16-byte blocks. It is widely used for secure data encryption. AES supports several operation modes, including ECB, CBC, and GCM, among others.
**What is ECB?**
ECB (Electronic Codebook) is one of the operation modes of AES-128. It determines how AES processes multiple data blocks. In ECB mode, the message is split into 16-byte blocks, and each block is encrypted or decrypted independently using the same key.
However, ECB does not use an Initialization Vector (IV), a random value that provides additional security. As a result, ECB is vulnerable to certain attacks, especially when encrypting repetitive or structured data.
In this exercise, we need to use **AES-128-ECB** because the cipher key is already provided.
***
### Resolution
First, we are going to create a file named `task7.py`
Understanding the code
* AES and base64 libraries are imported to handle AES decryption and Base64 decoding.
* The script opens the **7.txt** file with `open()` in read mode, assigning its content to the `encrypted_base64` variable.
* You can download the file using a terminal command:
* > 7.txt
* `encrypted_base64` is then Base64 decoded and stored in the `encrypted_bytes` variable.
* The `key` variable is initialized with the string YELLOW SUBMARINE, which is the decryption key provided in the challenge.
* `cipher` is created as a new AES object, where the `key` and `AES.MODE_ECB` are passed as parameters.
* `decrypted_bytes` is initialized by decrypting `encrypted_bytes` using the `cipher.decrypt()` method.
* `decrypted_text` is initialized with `decrypted_bytes` decoded to "UTF-8", converting the bytes to a readable string.
* Finally, `decrypted_text` is printed, revealing the plaintext message.
***
### Result
The result is the same that task 6.
