[IS] RSA cryptosystem

def gene(d, n):
    i = 0
    for i in range(1, n+1):
        if ((i*d)%n == 1):
            return i
    return 0

def encrypt(text, e, n):
    ctext = []
    for a in text:
        if (ord(a) >= 97 and ord(a) <= 122):
            c = int(((ord(a)-96)**e)%n)
            ctext.append(c)
        elif (a == ' '):
            ctext.append(0)

    return ctext

def decrypt(ctext, d, n):
    text = ''
    for c in ctext:
        if (c != 0):
            a = (c**d)%n
            text += chr(a+96)
        else:
            text += ' '
    return text

choose = int(raw_input("1 - encrypt; 2 - decrypt: "))
if choose == 1:
    p = int(input('input p: '))
    q = int(input('input q: '))
    n = p*q
    fin = (p-1)*(q-1)
    d = int(input('input d: '))
    e = gene(d, fin)

    with open("input.txt", "r") as f:
        text = f.read().lower()
        ct = encrypt(text, e, n)
        text = ""
        for el in ct:
            text += str(el) + ' '
        fo = open("output.txt", "w")
        fo.write(text)
        fo.close()
    print('n = ' + str(n))

elif (choose == 2):
    with open("input.txt", "r") as f:
        d = int(input('input d: '))
        n = int(input('input n: '))
        ctext = f.read()
        ctext = ctext.split()
        ct = []
        for c in ctext:
            ct.append(int(c))
        tx = decrypt(ct, d, n)
        print(tx)