Objective
Develop a Python program to encrypt or decrypt a BMP image file by swapping the "BM" signature in the first two bytes with "MB" and vice versa.
Utilize the advanced FileStream constructor to allow reading and writing at the same time.
Example Python Exercise
Show Python Code
# Python program to encrypt or decrypt a BMP file by swapping the "BM" signature
def encrypt_decrypt_bmp(filename):
try:
# Open the BMP file in binary read and write mode
with open(filename, 'r+b') as file:
# Read the first two bytes (the signature)
signature = file.read(2)
# Check if the signature is "BM"
if signature == b'BM':
print("Encrypting: Swapping 'BM' to 'MB'...")
# Move the file pointer back to the start
file.seek(0)
# Write "MB" to replace "BM"
file.write(b'MB')
elif signature == b'MB':
print("Decrypting: Swapping 'MB' to 'BM'...")
# Move the file pointer back to the start
file.seek(0)
# Write "BM" to replace "MB"
file.write(b'BM')
else:
print(f"Error: The file '{filename}' does not have a valid BMP signature.")
except FileNotFoundError:
print(f"Error: The file '{filename}' does not exist.")
except Exception as e:
print(f"Error: {str(e)}")
# Example usage
encrypt_decrypt_bmp("example.bmp")
Output
Encrypting: Swapping 'BM' to 'MB'...
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