IS Lab 1 - Progress So Far

IS/Lab/Lab1/q3_playfair.py

@@ -0,0 +1,87 @@
+def generate_playfair_matrix(key):
+    key = ''.join(sorted(set(key.upper()), key=key.upper().index))
+    alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    matrix = []
+
+    for char in key:
+        if char not in matrix and char != 'J':
+            matrix.append(char)
+
+    for char in alphabet:
+        if char not in matrix and char != 'J':
+            matrix.append(char)
+
+    playfair_matrix = [matrix[i:i+5] for i in range(0, len(matrix), 5)]
+    return playfair_matrix
+
+def find_pos(matrix, char):
+    for row_idx, row in enumerate(matrix):
+        if char in row:
+            col_idx = row.index(char)
+            return row_idx, col_idx
+    return None
+
+def prepare_text(text):
+    text = ''.join(filter(str.isalpha, text.upper()))
+    text = text.replace('J', 'I')
+    pairs = []
+    i = 0
+    while i < len(text):
+        if i + 1 < len(text) and text[i] != text[i+1]:
+            pairs.append(text[i:i+2])
+            i += 2
+        else:
+            pairs.append(text[i]+'X')
+            i += 1
+    return pairs
+
+def playfair_en(ptext, pfk):
+    matrix = generate_playfair_matrix(pfk)
+    ptext_pairs = prepare_text(ptext)
+
+    ctext = []
+    for pair in ptext_pairs:
+        r1, c1 = find_pos(matrix, pair[0])
+        r2, c2 = find_pos(matrix, pair[1])
+
+        if r1 == r2:
+            ctext.append(matrix[r1][(c1 + 1) % 5] + matrix[r2][(c2 + 1) % 5])
+        elif c1 == c2:
+            ctext.append(matrix[(r1 + 1) % 5][c1] + matrix[(r2 + 1) % 5][c2])
+        else:
+            ctext.append(matrix[r1][c2] + matrix[r2][c1])
+
+    return ''.join(ctext)
+
+def playfair_de(ctext, pfk):
+    matrix = generate_playfair_matrix(pfk)
+    ctext_pairs = prepare_text(ctext)
+
+    ptext = []
+    for pair in ctext_pairs:
+        r1, c1 = find_pos(matrix, pair[0])
+        r2, c2 = find_pos(matrix, pair[1])
+
+        if r1 == r2:
+            ptext.append(matrix[r1][(c1 - 1) % 5] + matrix[r2][(c2 - 1) % 5])
+        elif c1 == c2:
+            ptext.append(matrix[(r1 - 1) % 5][c1] + matrix[(r2 - 1) % 5][c2])
+        else:
+            ptext.append(matrix[r1][c2] + matrix[r2][c1])
+
+    return ''.join(ptext)
+
+def main():
+    ptext = input("Kindly enter your desired plaintext: ")
+    pfk = input("Kindly enter the Playfair Key: ")
+
+    print("Welcome to the Playfair cipher system.")
+    print("Plaintext: ", ptext)
+    print("Playfair Key: ", pfk)
+    ctext = playfair_en(ptext, pfk)
+    print("Ciphertext: ", ctext)
+    decrypted_text = playfair_de(ctext, pfk)
+    print("Decrypted Text: ", decrypted_text)
+
+if __name__ == '__main__':
+    main()