Add program for playfair cipher in python

systems/cryptography/playfair-cipher/python/playfair_c.py

@@ -0,0 +1,89 @@
+def main_func():
+    input_key = input("Enter the key:")
+    key = generate_key(input_key)
+    print(key)
+    p_t = input("Enter plaintext:")
+
+    cipher_text = encrypt(p_t, key)
+    print("Encrypted text:", cipher_text)
+
+    #plain_text = decrypt(cipher_text, key)
+    #print(plain_text)
+
+
+def generate_key(string):
+    key = []
+    for i in range(len(string)):
+        if not string[i] in key and string[i] != "j":
+            key.append(string[i])
+    remain = [chr(i) for i in range(ord('a'), ord('z') + 1) if not chr(i) in key and chr(i) != "j"]
+    key.extend(remain)
+    return [key[i:i + 5] for i in range(0, len(key), 5)]
+
+def encrypt(plain_t, key):
+    if not type(key) is list:
+        key = generate_key(key)
+    plain_t = plain_t.lower().replace(" ", "")
+    p_t_grouped = []
+    i = 0
+    while i < len(plain_t):
+        if i == len(plain_t) - 1:
+            p_t_grouped.append(list(plain_t[i:i + 2]))
+            i += 2
+            continue
+        if (plain_t[i] == plain_t[i + 1]):
+            plain_t = plain_t[:i + 1] + "x" + plain_t[i + 1:]
+        p_t_grouped.append(list(plain_t[i:i+ 2]))
+        i += 2 
+    if len(p_t_grouped[-1]) == 1:
+        p_t_grouped[-1].append("x")
+
+    cipher_t = ""
+    for i in range(len(p_t_grouped)):
+        for j in range(len(key)):
+            for k in range(len(key[j])):
+                if key[j][k] == p_t_grouped[i][0]:
+                    r1 = j
+                    c1 = k
+                if key[j][k] == p_t_grouped[i][1]:
+                    r2 = j
+                    c2 = k
+        if r1 == r2:
+            cipher_t += key[r1][(c1 + 1) % len(key[r1])]
+            cipher_t += key[r2][(c2 + 1) % len(key[r2])]
+        elif c1 == c2:
+            cipher_t += key[(r1 + 1) % len(key)][c1]
+            cipher_t += key[(r2 + 1) % len(key)][c2]
+        else:
+            cipher_t += key[r1][c2]
+            cipher_t += key[r2][c1]
+    return cipher_t
+def decrypt(cipher_t, key):
+    if not type(key) is list:
+        key = generate_key(key)
+    c_t_grouped = [list(cipher_t[i:i + 2]) for i in range(0, len(cipher_t), 2)]
+
+    plain_t = ""
+    for i in range(len(c_t_grouped)):
+        r1, r2 = None, None
+        c1, c2 = None, None
+        for j in range(len(key)):
+            for k in range(len(key[j])):
+                if key[j][k] == c_t_grouped[i][0]:
+                    r1 = j
+                    c1 = k
+                if key[j][k] == c_t_grouped[i][1]:
+                    r2 = j
+                    c2 = k
+        if r1 == r2:
+            plain_t += key[r1][(c1 - 1) % len(key[r1])]
+            plain_t += key[r2][(c2  - 1) % len(key[r2])]
+        elif c1 == c2:
+            plain_t += key[(r1 - 1) % len(key)][c1]
+            plain_t += key[(r2 - 1) % len(key)][c2]
+        else:
+            plain_t += key[r1][c2]
+            plain_t += key[r2][c1]
+    return plain_t
+
+main_func()