def generate_playfair_matrix(key): key = ''.join(sorted(set(key.upper()), key=key.upper().index)) alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ" # J omitted unique = [] for ch in key: if ch != 'J' and ch not in unique: unique.append(ch) 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): 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(ch for ch in text.upper() if ch.isalpha()).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()