When it comes to encryption, one of the most important aspects to consider is the choice of cipher. A cipher is a mathematical algorithm that is used to encrypt and decrypt data. AES (Advanced Encryption Standard) is a widely used and accepted encryption standard that is considered to be very secure.

In this article, we will be discussing the use of AES 128 CBC and AES 256 CBC with the correct key lengths. These ciphers are the only ones that are supported by certain systems and should be used when working with sensitive data.

AES 128 CBC and AES 256 CBC are both block ciphers, which means that they encrypt data in fixed-size blocks (128 bits for AES 128 and 256 bits for AES 256). The CBC (Cipher Block Chaining) mode is a mode of operation that is used to encrypt data in blocks. It works by XORing the plaintext block with the previous ciphertext block before encrypting it. This helps to ensure that even small changes in the plaintext will result in large changes in the ciphertext.

The key length of AES is an important aspect to consider when using the cipher. AES 128 uses a 128-bit key, while AES 256 uses a 256-bit key. The key length determines the security of the encryption. A longer key length provides a higher level of security, but also requires more processing power to encrypt and decrypt the data.

Here is an example of how to use AES 128 CBC with the correct key length in Python:

```
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
# Generate a random 128-bit key
key = os.urandom(16)
# Initialize the cipher
cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
encryptor = cipher.encryptor()
ciphertext = encryptor.update(plaintext) + encryptor.finalize()
```

And here is an example of how to use AES 256 CBC with the correct key length in Python:

```
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
# Generate a random 256-bit key
key = os.urandom(32)
# Initialize the cipher
cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
encryptor = cipher.encryptor()
ciphertext = encryptor.update(plaintext) + encryptor.finalize()
```

It is important to note that the above examples are for demonstration purposes only and should not be used in production systems without proper validation and testing.

In conclusion, AES 128 CBC and AES 256 CBC with the correct key lengths are the only supported ciphers for certain systems. These ciphers provide a high level of security and are widely accepted as secure encryption standards. It is important to choose the correct cipher and key length when working with sensitive data.

In addition to the information provided in the previous article, it is important to note that the key used for AES encryption should be a random and unique value for each encryption. Additionally, the initialization vector (IV) used in the CBC mode should also be a random and unique value for each encryption.

When working with AES encryption, it is also important to consider the use of a key derivation function (KDF) to derive the encryption key from a password or passphrase. A KDF is a one-way function that can be used to derive an encryption key from a password or passphrase in a secure manner. The most common KDFs used with AES encryption are PBKDF2 (Password-Based Key Derivation Function 2) and bcrypt.

Another important aspect to consider when using AES encryption is the use of authenticated encryption. Authenticated encryption provides both confidentiality and integrity for the encrypted data. It ensures that the data has not been tampered with or altered in any way. The most common mode of operation that provides authenticated encryption is GCM (Galois/Counter Mode).

Here is an example of how to use AES 128 GCM with the correct key length in Python:

```
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
# Generate a random 128-bit key
key = os.urandom(16)
# Generate a random 96-bit IV
iv = os.urandom(12)
# Initialize the cipher
cipher = Cipher(algorithms.AES(key), modes.GCM(iv), backend=default_backend())
encryptor = cipher.encryptor()
ciphertext = encryptor.update(plaintext) + encryptor.finalize()
tag = encryptor.tag
```

It is important to store the tag along with the ciphertext as it will be needed for decryption and data integrity verification

In summary, AES encryption is a widely used and accepted encryption standard that provides a high level of security. When using AES encryption, it is important to use a unique and random key and IV for each encryption, to use a key derivation function to derive the encryption key from a password or passphrase, to use authenticated encryption mode like GCM, and to properly store the key, IV, and tag. It is also important to validate and test any encryption implementation before deploying it in a production system.

## Popular questions

- What is a cipher in encryption?

- A cipher is a mathematical algorithm that is used to encrypt and decrypt data.

- What is the difference between AES 128 CBC and AES 256 CBC?

- Both AES 128 CBC and AES 256 CBC are block ciphers, which means that they encrypt data in fixed-size blocks (128 bits for AES 128 and 256 bits for AES 256). The main difference is the key length, AES 128 uses a 128-bit key, while AES 256 uses a 256-bit key.

- Why is the key length important in AES encryption?

- The key length determines the security of the encryption. A longer key length provides a higher level of security, but also requires more processing power to encrypt and decrypt the data.

- What is the purpose of the initialization vector (IV) in CBC mode?

- The IV is used in the CBC mode to ensure that even small changes in the plaintext will result in large changes in the ciphertext. It works by XORing the plaintext block with the previous ciphertext block before encrypting it.

- Why is authenticated encryption important when using AES encryption?

- Authenticated encryption provides both confidentiality and integrity for the encrypted data. It ensures that the data has not been tampered with or altered in any way. It is important to use authenticated encryption mode like GCM when working with sensitive data.

### Tag

AES