AES Cipher¶

Symmetric encryption using Fernet (AES-128-CBC).

Class: AESCipher¶

from encryptocli.encryption.aes import AESCipher

cipher = AESCipher()

Methods¶

encrypt(plaintext, password)¶

Encrypt plaintext using AES-128-CBC with password derivation.

Parameters: - plaintext (str): Text to encrypt - password (str): Encryption password (any length)

Returns: str - Base64-encoded encrypted data

Raises: - EncryptionError - If encryption fails

Example:

cipher = AESCipher()
encrypted = cipher.encrypt("sensitive data", "my_password")
print(encrypted)

decrypt(ciphertext, password)¶

Decrypt ciphertext using provided password.

Parameters: - ciphertext (str): Base64-encoded encrypted data - password (str): Decryption password

Returns: str - Decrypted plaintext

Raises: - DecryptionError - If password is wrong or data is corrupted - InvalidInputError - If ciphertext format is invalid

Example:

cipher = AESCipher()
try:
    decrypted = cipher.decrypt(encrypted, "my_password")
except DecryptionError:
    print("Wrong password")

Security Details¶

Key Derivation¶

Algorithm: PBKDF2
Hash: SHA-256
Iterations: 100,000
Salt: 16 random bytes

Encryption¶

Algorithm: AES-128 in CBC mode
Block Size: 128 bits (16 bytes)
IV: 16 random bytes per encryption
Padding: PKCS7

Authentication¶

HMAC-SHA256 for authentication
Prevents tampering detection

Output Format¶

Encrypted output is base64-encoded for safe transmission:

base64(salt + iv + ciphertext + hmac)

Password Security¶

Password Requirements¶

Minimum: 6 characters
Recommended: 12+ characters
Strong: Mix uppercase, lowercase, numbers, symbols

Password Quality¶

Longer passwords are more secure
Use unique passwords for different data
Avoid dictionary words
Avoid personal information

Password Storage¶

Never hardcode passwords in source code
Use environment variables or secure vaults
Never commit passwords to version control

Usage Examples¶

Encrypt and Decrypt Text¶

from encryptocli.encryption.aes import AESCipher
from encryptocli.util.exceptions import DecryptionError

cipher = AESCipher()

# Encrypt
plaintext = "This is a secret message"
password = "secure_password_123"
encrypted = cipher.encrypt(plaintext, password)
print(f"Encrypted: {encrypted[:50]}...")

# Decrypt
try:
    decrypted = cipher.decrypt(encrypted, password)
    print(f"Decrypted: {decrypted}")
except DecryptionError:
    print("Decryption failed - wrong password or corrupted data")

Encrypt File Contents¶

from encryptocli.encryption.aes import AESCipher

cipher = AESCipher()

# Read file
with open("document.txt", "r") as f:
    content = f.read()

# Encrypt
encrypted = cipher.encrypt(content, "password123")

# Save encrypted
with open("document.enc", "w") as f:
    f.write(encrypted)

Decrypt File¶

from encryptocli.encryption.aes import AESCipher

cipher = AESCipher()

# Read encrypted file
with open("document.enc", "r") as f:
    encrypted = f.read()

# Decrypt
decrypted = cipher.decrypt(encrypted, "password123")

# Save decrypted
with open("document.txt", "w") as f:
    f.write(decrypted)

Error Handling¶

from encryptocli.encryption.aes import AESCipher
from encryptocli.util.exceptions import (
    EncryptionError,
    DecryptionError,
    InvalidInputError
)

cipher = AESCipher()

try:
    encrypted = cipher.encrypt("data", "password")
except EncryptionError as e:
    print(f"Encryption error: {e}")

try:
    decrypted = cipher.decrypt(encrypted, "wrong_password")
except DecryptionError as e:
    print(f"Decryption failed: {e}")
except InvalidInputError as e:
    print(f"Invalid data format: {e}")

Performance¶

Works efficiently with typical data sizes
Key derivation involves intentional computation delay for security

Compatibility¶

Works with any text-based data
Output is portable across platforms
Encrypted data can be transmitted via email, chat, etc.
Recipient needs same AESCipher class to decrypt

Limitations¶

Symmetric encryption (same password to encrypt/decrypt)
Not suitable for public key distribution
Password must be remembered or stored securely
No built-in key management