Make decrypt_file return the plaintext content

Signed-off-by: Tiago Garcia <tiago.rgarcia@ua.pt>

delivery2/lib/symmetric_encryption.py

@@ -35,6 +35,8 @@ def encrypt_file(input_file, output_file=None):
 
 # Function to decrypt a file
 def decrypt_file(key, input_file, output_file=None):
+    plaintext_content = b""
+
     with open(input_file, 'rb') as infile:
         # Read the IV from the input file
         iv = infile.read(16)
@@ -46,9 +48,19 @@ def decrypt_file(key, input_file, output_file=None):
                 while chunk := infile.read(2048):
                     plaintext = decryptor.update(chunk)
                     outfile.write(plaintext)
+                    plaintext_content += plaintext
 
                 # Finalize decryption
-                outfile.write(decryptor.finalize())
+                final_chunk = decryptor.finalize()
+                outfile.write(final_chunk)
+                plaintext_content += final_chunk
+        else:
+            while chunk := infile.read(2048):
+                plaintext = decryptor.update(chunk)
+                plaintext_content += plaintext
 
-    return True
+            # Finalize decryption
+            plaintext_content += decryptor.finalize()
+
+    return plaintext_content