In this activity, we are going to extend the program you made earlier to add a decryption feature. After prompting the user for the phrase and shift amount, ask them if they would like to encrypt or decrypt their message. Your program should then perform the correct procedure and print the results.

Answer 1

Here is a Python program that prompts the user for a phrase, shift amount, and whether they want to encrypt or decrypt the message:

```python
def caesar_cipher(text, shift, encrypt=True):
result = ""

shift = shift % 26

if not encrypt:
shift = -shift

for char in text:
if char.isalpha():
if char.islower():
result += chr((ord(char) - ord('a') + shift) % 26 + ord('a'))
else:
result += chr((ord(char) - ord('A') + shift) % 26 + ord('A'))
else:
result += char

return result

def main():
phrase = input("Enter a phrase: ")
shift = int(input("Enter a shift amount: "))
choice = input("Would you like to encrypt or decrypt the message? (encrypt/decrypt): ")

if choice == "encrypt":
result = caesar_cipher(phrase, shift)
print("Encrypted message:", result)
elif choice == "decrypt":
result = caesar_cipher(phrase, shift, False)
print("Decrypted message:", result)
else:
print("Invalid choice. Please enter either 'encrypt' or 'decrypt'.")

if __name__ == "__main__":
main()
```

You can copy and paste this code into a Python environment to run it. The program will prompt the user for a phrase, shift amount, and whether they want to encrypt or decrypt the message. Based on their choice, the program will either encrypt or decrypt the input message using the Caesar cipher algorithm and print the result.