basic encryption tutorial

Author: philtabor

basic_encryption/caesar.py

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+from common import alphabet
+
+
+def translate(message, shift, encrypt=True):
+    new_message = ''
+    n_chars = len(alphabet)
+
+    for character in message:
+        char_idx = alphabet.index(character)
+        if encrypt:
+            new_char_idx = (char_idx + shift) % n_chars
+        elif not encrypt:
+            new_char_idx = (char_idx - shift) % n_chars
+        new_message += alphabet[new_char_idx]
+    return new_message
+
+
+cipher_shift = 7
+
+print('AB->', translate('AB', cipher_shift))
+print('ab->', translate('ab', cipher_shift))
+print('Ab->', translate('Ab', cipher_shift))
+print('aB->', translate('aB', cipher_shift))
+
+plaintext = 'This is an encrypted message.'
+ciphertext = translate(plaintext, cipher_shift, True)
+print(plaintext, '->', ciphertext)
+original_message = translate(ciphertext, cipher_shift, False)
+print(ciphertext, '->', original_message)

basic_encryption/common.py

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+import random
+
+
+def character_generator(start_char, stop_char):
+    for char in range(ord(start_char), ord(stop_char)+1):
+        yield chr(char)
+
+
+def generate_one_time_pad(n_chars, characters):
+    return ''.join(random.choice(characters) for _ in range(n_chars))
+
+
+lower_case = list(character_generator('a', 'z'))
+upper_case = list(character_generator('A', 'Z'))
+punctuation = ['.', ',', ' ', '?', '!']
+
+alphabet = lower_case + upper_case + punctuation

basic_encryption/one_time_pad.py

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+from common import alphabet, generate_one_time_pad
+
+
+def translate(message, one_time_pad, encrypt=True):
+    new_message = ''
+
+    n_chars = len(alphabet)
+
+    for src, key in zip(message, one_time_pad):
+        char_idx = alphabet.index(src)
+        pad_idx = alphabet.index(key)
+        if encrypt:
+            new_char_idx = (char_idx + pad_idx) % n_chars
+        elif not encrypt:
+            new_char_idx = (char_idx - pad_idx) % n_chars
+        new_message += alphabet[new_char_idx]
+
+    return new_message
+
+
+message = 'This is an encrypted message.'
+secret_key = generate_one_time_pad(len(message), alphabet)
+encrypted_message = translate(message, secret_key, True)
+original_message = translate(encrypted_message, secret_key, False)
+
+print(message, '->', encrypted_message)
+print(encrypted_message, '->', original_message)

basic_encryption/vignere.py

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+from common import alphabet, generate_one_time_pad
+
+
+def make_vignere_table():
+    table = [['']] * len(alphabet)
+    for idx, character in enumerate(alphabet):
+        row = []
+        for char in alphabet[idx:]:
+            row.append(char)
+        for char in alphabet[:idx]:
+            row.append(char)
+        table[idx] = row
+    return table
+
+
+def translate(message, vig_table, one_time_pad, encrypt=True):
+    new_message = ''
+
+    if encrypt:
+        for src, key in zip(message, one_time_pad):
+            row = vig_table[:][0].index(key)
+            col = vig_table[0][:].index(src)
+            new_message += vig_table[row][col]
+    elif not encrypt:
+        for src, key in zip(message, one_time_pad):
+            row = vig_table[:][0].index(key)
+            col = vig_table[row][:].index(src)
+            new_message += vig_table[0][col]
+    return new_message
+
+
+table = make_vignere_table()
+message = 'This is an encrypted message.'
+secret_key = generate_one_time_pad(len(message), alphabet)
+encrypted_message = translate(message, table, secret_key, True)
+original_message = translate(encrypted_message, table, secret_key, False)
+
+print(message, '->', encrypted_message)
+print(encrypted_message, '->', original_message)