The VMS as a possible chain encryption ( Mod 23 ).

Code:
# Reduced alphabet: No J, U, W
alphabet = list("ABCDEFGHIKLMNOPQRSTVXYZ")  # 23 letters

def char_to_pos(c):
    return alphabet.index(c.upper()) + 1

def pos_to_char(p):
    p = (p - 1) % len(alphabet) + 1
    return alphabet[p - 1]

def chain_decrypt_verbose(ciphertext):
    ciphertext = ciphertext.upper()
    decrypted = ""
    table = []

    prev_cipher_pos = 0
    for i, c in enumerate(ciphertext, start=1):
        if c not in alphabet:
            decrypted += c
            table.append([i, c])  # Nur zwei Spalten für Nicht-Buchstaben
            continue

        cipher_pos = char_to_pos(c)
        plain_pos = (cipher_pos - prev_cipher_pos) % len(alphabet)
        if plain_pos == 0:
            plain_pos = len(alphabet)
        plain_char = pos_to_char(plain_pos)

        decrypted += plain_char

        table.append([
            i,
            c,
            cipher_pos,
            plain_char,
            plain_pos,
            prev_cipher_pos,
            f"({cipher_pos} - {prev_cipher_pos}) mod {len(alphabet)} = {plain_pos}"
        ])

        prev_cipher_pos = cipher_pos

    return decrypted, table

def print_table(table):
    print("\nDecryption Table:")
    print("-" * 90)
    print(f"{'i':>3} | {'Cipher':^9} | {'cᵢ':^4} | {'Plain':^9} | {'pᵢ':^4} | {'cᵢ₋₁':^6} | {'Computation':<30}")
    print("-" * 90)
    for row in table:
        if len(row) == 7:
            i, cchar, cpos, pchar, ppos, cprev, calc = row
            print(f"{i:>3} | {cchar:^9} | {cpos:^4} | {pchar:^9} | {ppos:^4} | {cprev:^6} | {calc:<30}")
        elif len(row) == 2:
            i, cchar = row
            print(f"{i:>3} | {cchar:^9} | {'-':^4} | {'-':^9} | {'-':^4} | {'-':^6} | {'(not a letter)':<30}")
    print("-" * 90)

def apply_fixed_substitution(text, from_list, to_list):
    mapping = dict(zip(from_list, to_list))
    substituted = ''.join(mapping.get(c, c) for c in text)
    return substituted, mapping

if __name__ == "__main__":
    text = input("? Enter ciphertext to decrypt (only letters A–Z, excluding J, U, W): ")
    decrypted, table = chain_decrypt_verbose(text)
    print(f"\n? Decrypted text: {decrypted}")
    print_table(table)

    # Substitution: Voynich → Latein
    voynich_order = list("OEHYACDIKLRSTNQPMFGXBVZ")
    latin_order  = list("IEAUTSRNOMCLPDBQGVFHXYZ")
    substituted, mapping = apply_fixed_substitution(decrypted, voynich_order, latin_order)

    print("\n? Substituted (Voynich → Latin):")
    print(substituted)

    print("\n?️ Substitution Map:")
    for voy, lat in mapping.items():
        print(f"  {voy} → {lat}")