I’m kind of a beginner still and I’m making a simple password manager in python using the cryptography module. The user can enter a program name and a password, and it is encrypted and then written to a file. They can also view passwords added to the file. When the user selects this, they enter the name of the program/service they are trying to find, and it returns the matching password by decrypting the file line by line and checking if the program name is in that file. I hope this makes sense.

The issue I’m having is I get raise InvalidToken cryptography.fernet.InvalidToken when the program attempts to decrypt lines from the file after selecting “view” and entering a name, even when the file is not empty. I’m really unsure why, as the key is not generated in the program, it is stored in a file so the same key is read each time the program runs. I am already reading the file in bytes, not strings. I also have another simpler program which uses the same file and can successfully encrypt and decrypt from a file so I have a feeling I’ve made a mistake somewhere else.

Here is my program (error occurs at line 58):

from cryptography.fernet import Fernet

#Get key from file
filekey = open("filekey.key", "rb")
key = filekey.read()
fernet = Fernet(key)
filekey.close()

cmd = "" #Force entry to loop

#Run until user quits
while cmd != "quit":
    cmd = input("[add | view | quit] ")

    #Input validation loop
    while cmd not in ["add", "view", "quit"]:
        print("Not a valid command. Try again.")
        cmd = input("[add | view | quit]")

    #Run if user enters "add"
    if cmd == "add":

        #Get user input for name and password
        name = input("Enter name: ")
        pwd = input("Enter password: ")

        #Concatenate and encode input
        new_line = name + " " + pwd
        byte_new_line = new_line.encode()

        #Encrypt and convert to string
        enc_line = fernet.encrypt(byte_new_line)
        enc_line_str = str(enc_line)

        #Write string to file
        outfile = open("passwords.data", "a")
        outfile.write(enc_line_str)
        outfile.close()
    
    #Run if user enters "view"
    if cmd == "view":
        found = False #Keep track of whether name is present in file

        #Get user input for name to find
        search = input("Name to search for: ")

        #Open file to search from
        infile = open("passwords.data", "rb")
        line = infile.readline()
        
        #Read each line of file
        while line != "":
            line = infile.readline()

            #Decrypt line and convert to string
            line_dec = fernet.decrypt(line) #Error here
            line_dec_str = str(line_dec)

            #Get index of name in decoded string
            index = line_dec_str.find(name)

            #Run if name is found in string
            if index != -1:

                #Change found to True and print string
                found = True
                print(line_dec_str)

        #Display error if name not found
        if found == False:
            print("Error: name not found in file. Try again.")

        infile.close()

Any help would be greatly appreciated ☺️