如何从文件中解码编码为 base64 的行？

Question

I need to decode lines from a file.

Here is my code so far:

    def decode(self) -> list:
        """
        Decode file with key.

        For correct answer you have to convert file lines from base64 to utf-8.

        To decode one line you have to take a UNICODE value of a letter, subtract cipher step and take mod of 255.
        After that you have to convert that number back to a character.
        Example: key = 'test', decoded_data = "+%'"
        '+' -> (43 - 448) % 255 -> 'i' -> ... -> 'ice'

        :return: List of decoded lines
        """
        decoded_lines1 = []
        decoded_lines = []
        lines = self.read_code_from_file()
        for line in lines:
            decoded_lines.append(base64.b64decode(line).decode())
        for decoded_line in decoded_lines:
            for letter in decoded_line:
                decoded_lines1.append(chr((ord(letter) - sum([ord(i) for i in self.key])) % 255))
        return decoded_lines1

decoded_lines:

[')-.7)-\x06\x06AOO', '-57)-0\x06\x06JASJAOOASJ', ')07)2\x06\x06AJSAJAJOAJJAAO',...]

My output for some reason has all the letters individually, the small portion of output below is equal to the first list element of decoded_lines after decoding My output:

['-', '1', '2', ';', '-', '1', '\n', '\n', 'E', 'S', 'S', ...]

Expected output:

['-12;-1\n\nESS', ...]

Is there any way to have the lines seperated by commas rather than each letter seperated by commas? The non-hardcoded key is equal to 1016.

Answer 1

The problem is that you append each character, one-by-one to decoded_lines1 when you do

.append(chr((ord(letter) - sum([ord(i) for i in self.key])) % 255))

Instead, you want to do this to each character in decoded_line , make one string out of all the decoded characters, and then append that string to decoded_lines1 .

for decoded_line in decoded_lines:
    new_line = []
    for letter in decoded_line:
       new_line.append(chr((ord(letter) - sum([ord(i) for i in self.key])) % 255))
    decoded_lines1.append("".join(new_line))

But you can simplify your code further by combining the for line in lines and for decoded_line in decoded_lines loops:

def decode(self):
    decoded_lines = []
    lines = self.read_code_from_file()
    for line in lines:
        decoded_line = base64.b64decode(line).decode()
        new_line = []
        for letter in decoded_line:
            new_line.append(chr((ord(letter) - sum([ord(i) for i in self.key])) % 255))
        decoded_lines.append("".join(new_line))
    return decoded_lines

Answer 2

The problem lies in below code:

for decoded_line in decoded_lines:
    for letter in decoded_line:
        decoded_lines1.append(chr((ord(letter) - sum([ord(i) for i in self.key])) % 255))

Here, you are appending letter by letter to the list while you want to append decoded line into the list.

So, I have stored decoded letters into one string and then append it to the list.

for decoded_line in decoded_lines:
            temp=""
            for letter in decoded_line:
                temp=temp+chr((ord(letter) - sum([ord(i) for i in self.key])) % 255)
            decoded_lines1.append(temp)

Final code will be like below:

def decode(self) -> list:
        """
        Decode file with key.

        For correct answer you have to convert file lines from base64 to utf-8.

        To decode one line you have to take a UNICODE value of a letter, subtract cipher step and take mod of 255.
        After that you have to convert that number back to a character.
        Example: key = 'test', decoded_data = "+%'"
        '+' -> (43 - 448) % 255 -> 'i' -> ... -> 'ice'

        :return: List of decoded lines
        """
        decoded_lines1 = []
        decoded_lines = []            
        lines = self.read_code_from_file()
        for line in lines:
            decoded_lines.append(base64.b64decode(line).decode())
        for decoded_line in decoded_lines:
            temp=""
            for letter in decoded_line:
                temp=temp+chr((ord(letter) - sum([ord(i) for i in self.key])) % 255)
            decoded_lines1.append(temp)                
        return decoded_lines1

Answer 3

Do you have only a single word in a line? it is a sentence of words? It consists of multiple words then your second loop should be on words then 3rd lop should be on letters. The code should be something like this

def decode(self) -> list:
        """
        Decode file with key.

        For correct answer you have to convert file lines from base64 to utf-8.

        To decode one line you have to take a UNICODE value of a letter, subtract cipher step and take mod of 255.
        After that you have to convert that number back to a character.
        Example: key = 'test', decoded_data = "+%'"
        '+' -> (43 - 448) % 255 -> 'i' -> ... -> 'ice'

        :return: List of decoded lines
        """
        decoded_lines1 = []
        decoded_lines = []
        lines = self.read_code_from_file()
        for line in lines:
            decoded_lines.append(base64.b64decode(line).decode())
        for decoded_line in decoded_lines:
            for word in decoded_line.split():
                docoded_word=''
                for letter in word:
                    docoded_word+=(chr((ord(letter) - sum([ord(i) for i in self.key])) % 255))
                decoded_lines1.append(docoded_word)
        return (decoded_lines1)