replace base64_cipher.py with an easy to understand version

ciphers/base64.py

@@ -0,0 +1,105 @@
+B64_CHARSET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+
+
+def base64_encode(data: bytes) -> str:
+    """Encodes data according to RFC4648.
+
+    The data is first transformed to binary and appended with binary digits so that its
+    length becomes a multiple of 6, then each 6 binary digits will match a character in
+    the B64_CHARSET string. The number of appended binary digits would later determine
+    how many "=" sign should be added, the padding.
+    For every 2 binary digits added, a "=" sign is added in the output.
+    We can add any binary digits to make it a multiple of 6, for instance, consider the
+    following example:
+    "AA" -> 0010100100101001 -> 001010 010010 1001
+    As can be seen above, 2 more binary digits should be added, so there's 4
+    possibilities here: 00, 01, 10 or 11.
+    That being said, Base64 encoding can be used in Steganography to hide data in these
+    appended digits.
+
+    >>> base64_encode(b"This pull request is part of Hacktoberfest20!")
+    'VGhpcyBwdWxsIHJlcXVlc3QgaXMgcGFydCBvZiBIYWNrdG9iZXJmZXN0MjAh'
+    >>> base64_encode(b"https://tools.ietf.org/html/rfc4648")
+    'aHR0cHM6Ly90b29scy5pZXRmLm9yZy9odG1sL3JmYzQ2NDg='
+    >>> base64_encode(b"A")
+    'QQ=='
+    """
+    binary_stream = "".join(bin(char)[2:].zfill(8) for char in data)
+
+    padding_needed = len(binary_stream) % 6 != 0
+
+    if padding_needed:
+        # The padding that will be added later
+        padding = "=" * ((6 - len(binary_stream) % 6) // 2)
+
+        # Append binary_stream with arbitrary binary digits (0's by default) to make its
+        # length a multiple of 6.
+        binary_stream += "0" * (6 - len(binary_stream) % 6)
+
+    # Encode every 6 binary digits to their corresponding Base64 character
+    encoded_data = "".join(
+        B64_CHARSET[int(binary_stream[index : index + 6], 2)]
+        for index in range(0, len(binary_stream), 6)
+    )
+
+    if padding_needed:
+        return encoded_data + padding
+    else:
+        return encoded_data
+
+
+def base64_decode(encoded_data: str) -> bytes:
+    """Decodes data according to RFC4648.
+
+    This does the reverse operation of base64_encode.
+    We first transform the encoded data back to a binary stream, take off the
+    previously appended binary digits according to the padding, at this point we
+    would have a binary stream whose length is multiple of 8, the last step is
+    to convert every 8 bits to a byte.
+
+    >>> base64_decode("VGhpcyBwdWxsIHJlcXVlc3QgaXMgcGFydCBvZiBIYWNrdG9iZXJmZXN0MjAh")
+    b'This pull request is part of Hacktoberfest20!'
+    >>> base64_decode("aHR0cHM6Ly90b29scy5pZXRmLm9yZy9odG1sL3JmYzQ2NDg=")
+    b'https://tools.ietf.org/html/rfc4648'
+    >>> base64_decode("QQ==")
+    b'A'
+    """
+    padding = encoded_data.count("=")
+
+    # Check if the encoded string contains non base64 characters
+    if padding:
+        assert all(
+            char in B64_CHARSET for char in encoded_data[:-padding]
+        ), "Invalid base64 character(s) found."
+    else:
+        assert all(
+            char in B64_CHARSET for char in encoded_data
+        ), "Invalid base64 character(s) found."
+
+    # Check the padding
+    assert len(encoded_data) % 4 == 0 and padding < 3, "Incorrect padding."
+
+    if padding:
+        # Remove padding if there is one
+        encoded_data = encoded_data[:-padding]
+
+        binary_stream = "".join(
+            bin(B64_CHARSET.index(char))[2:].zfill(6) for char in encoded_data
+        )[: -padding * 2]
+    else:
+        binary_stream = "".join(
+            bin(B64_CHARSET.index(char))[2:].zfill(6) for char in encoded_data
+        )
+
+    data = [
+        int(binary_stream[index : index + 8], 2)
+        for index in range(0, len(binary_stream), 8)
+    ]
+
+    return bytes(data)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

quantum/single_qubit_measure.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 """
-Build a simple bare-minimum quantum circuit that starts with a single 
-qubit (by default, in state 0), runs the experiment 1000 times, and 
+Build a simple bare-minimum quantum circuit that starts with a single
+qubit (by default, in state 0), runs the experiment 1000 times, and
 finally prints the total count of the states finally observed.
 Qiskit Docs: https://qiskit.org/documentation/getting_started.html
 """