shortened pf

IS/Lab/Lab1/q3_playfair.py

@@ -1,81 +1,46 @@
-def generate_playfair_matrix(key):
+def keymat(k):
-    key = ''.join(sorted(set(key.upper()), key=key.upper().index))
+    k = k.upper().replace('J', 'I')
-    alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"  # J omitted
+    seen = set(); seq = []
-    unique = []
+    for ch in (k + "ABCDEFGHIKLMNOPQRSTUVWXYZ"):
-    for ch in key:
+        if ch.isalpha() and ch not in seen:
-        if ch != 'J' and ch not in unique:
+            seen.add(ch); seq.append(ch)
-            unique.append(ch)
+    return [seq[i:i+5] for i in range(0, 25, 5)]
-    for ch in alphabet:
-        if ch not in unique:
-            unique.append(ch)
-    return [unique[i:i+5] for i in range(0, 25, 5)]
 
-def find_pos(matrix, char):
+def pairs(s, prep=True):
-    for row_idx, row in enumerate(matrix):
+    s = ''.join(ch for ch in s.upper() if ch.isalpha())
-        if char in row:
+    if prep:
-            col_idx = row.index(char)
+        s = s.replace('J', 'I')
-            return row_idx, col_idx
+        p = []; i = 0
-    return None
+        while i < len(s):
-
+            a = s[i]; b = s[i+1] if i+1 < len(s) else 'X'
-def prepare_text(text):
+            if a == b:
-    text = ''.join(ch for ch in text.upper() if ch.isalpha()).replace('J', 'I')
+                p.append(a + 'X'); i += 1
-    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')
+                p.append(a + b); i += 2
-            i += 1
+        return p
-    return pairs
+    return [s[i:i+2] for i in range(0, len(s), 2)]
-
-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])
 
+def playfair(text, key, enc=True):
+    m = keymat(key)
+    pos = {m[r][c]: (r, c) for r in range(5) for c in range(5)}
+    out = []
+    for a, b in pairs(text, prep=enc):
+        r1, c1 = pos[a]; r2, c2 = pos[b]
         if r1 == r2:
-            ctext.append(matrix[r1][(c1 + 1) % 5] + matrix[r2][(c2 + 1) % 5])
+            out.append(m[r1][(c1 + (1 if enc else -1)) % 5] +
+                       m[r2][(c2 + (1 if enc else -1)) % 5])
         elif c1 == c2:
-            ctext.append(matrix[(r1 + 1) % 5][c1] + matrix[(r2 + 1) % 5][c2])
+            out.append(m[(r1 + (1 if enc else -1)) % 5][c1] +
+                       m[(r2 + (1 if enc else -1)) % 5][c2])
         else:
-            ctext.append(matrix[r1][c2] + matrix[r2][c1])
+            out.append(m[r1][c2] + m[r2][c1])
+    return ''.join(out)
 
-    return ''.join(ctext)
+enc = lambda pt, k: playfair(pt, k, True)
-
+dec = lambda ct, k: playfair(ct, k, False)
-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()
+    pt = input("Plaintext: ")
+    k  = input("Key: ")
+    ct = enc(pt, k); print("Ciphertext:", ct)
+    print("Decrypted:", dec(ct, k))