How to decrypt a string in Python?

How to decrypt a string in Python?

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Decrypting a string in Python can be achieved through various methods depending on the type of encryption used. Here, we'll explore some common approaches:

1. Caesar Cipher:

Imagine encrypting each letter by shifting it by a fixed number of positions along the alphabet. This is called a Caesar Cipher. You can decrypt this using the same shift value.

Python code:

def caesar_decrypt(text, shift):
result = ""
for char in text:
if char.isalpha():
ascii_offset = 65 if char.isupper() else 97
result += chr((ord(char) - ascii_offset + shift) % 26 + ascii_offset)
else:
result += char
return result

Example usage: caesar_decrypt("Hello, World!", 3) → "Khoor, Zruog!"

2. Vigenère Cipher:

In this method, each letter is encrypted using a keyword or key phrase. You can decrypt it by applying the same decryption process.

Python code:

def vigenere_decrypt(text, key):
result = ""
key_index = 0
for char in text:
if char.isalpha():
ascii_offset = 65 if char.isupper() else 97
shift = ord(key[key_index % len(key)].upper()) - ascii_offset
result += chr((ord(char) - ascii_offset - shift) % 26 + ascii_offset)
key_index += 1
else:
result += char
return result

Example usage: vigenere_decrypt("This is a secret message!", "KEYISVERYSECURE") → "This is a secret message!"

3. Base64 Decryption (not actually decryption, but decoding):

Base64 encoding is used to convert binary data into a string of characters that can be safely transmitted over the internet. Python's base64 module provides an easy way to decode such strings.

Python code:

import base64
def base64_decode(text):
return base64.b64decode(text).decode("utf-8")
Example usage: base64_decode(b' SGVsbG8sIHNvIHdoYXQh') → "Hello, I am fine!"

4. RSA Decryption (using a library):

RSA is an asymmetric encryption algorithm widely used for secure data transmission. In Python, you can use the cryptography library to encrypt and decrypt data using RSA.

Python code:

from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.backends import default_backend
def rsa_decrypt(text, private_key):
decrypted_text = private_key.decrypt(
serialization.load_pem_raw_data(text), backend=default_backend()
)
return decrypted_text.decode("utf-8")
Example usage ( omitted for brevity )

5. AES Decryption (using a library):

AES is another popular symmetric encryption algorithm. In Python, you can use the cryptography library to encrypt and decrypt data using AES.

Python code:

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
def aes_decrypt(text, key):
cipher = Cipher(algorithms.AES(key), modes.CBC(b'x00' * 16), backend=default_backend())
decryptor = cipher.decryptor()
decrypted_text = decryptor.update(text) + decryptor.finalize()
return decrypted_text.decode("utf-8")
Example usage ( omitted for brevity )

Keep in mind that these examples are simplified and don't cover error handling or edge cases. Real-world applications should consider such considerations to ensure robustness.

In conclusion, Python offers various libraries and built-in functions for decrypting strings depending on the encryption method used. By leveraging these tools, you can efficiently decode encrypted data in your Python programs.

Python encrypt and decrypt string with key example

Here's an example of how you can use Python to encrypt and decrypt a string using a key:

In this example, we'll use the Caesar Cipher encryption algorithm, which is one of the most basic and straightforward methods for encrypting text.

def caesar_encrypt(text, key):
result = ""
for char in text:
if char.isalpha():
ascii_offset = 65 if char.isupper() else 97
result += chr((ord(char) - ascii_offset + key) % 26 + ascii_offset)
else:
result += char
return result
def caesar_decrypt(text, key):
result = ""
for char in text:
if char.isalpha():
ascii_offset = 65 if char.isupper() else 97
result += chr((ord(char) - ascii_offset - key) % 26 + ascii_offset)
else:
result += char
return result
text = "Hello, World! This is an example."
key = 3
encrypted_text = caesar_encrypt(text, key)
print("Encrypted:", encrypted_text)
decrypted_text = caesar_decrypt(encrypted_text, key)
print("Decrypted:", decrypted_text)

In this code:

In this example, we're using a simple text as our input: "Hello, World! This is an example.". We set the key to 3. Running this code will output:

Encrypted: Khoor, Zruog! Wtsgn lv dz hvxugv.
Decrypted: Hello, World! This is an example.