алгоритм отладки RSA

Question

Я написал следующий алгоритм RSA, который использует два целочисленных ввода для определения интервала, в котором нужно искать простые числа, чтобы начать алгоритм:

import math
import random
import fractions

def get_primes_in_range(low, high):
    while True:
        try:
            if low < 130:
                low = int(input("Sorry, the lower bound must be at least 130 to ensure large primes. Please reenter a value for the lower bound of your prime search: "))
        except ValueError:
            continue
        if low < 130:
            continue
        else: 
            break
    while True:
        try:
            if high <= low:
                high = int(input("Sorry, the higher bound for your prime search must at least be larger than the lower bound. Please reenter a value for the upper bound of your prime search: "))
        except ValueError:
            continue
        if high <= low:
            continue
        else:
            break
    primes = []
    while len(primes) < 3:
        high = (high + 1)
        for x in range(low, high+1):
            if x > 1:
                for n in range(2, x):
                    if (x % n) == 0:
                        break
                else:
                    primes.append(x)
    return primes

def are_relatively_prime(phi, E):
    return fractions.gcd(phi, E) == 1

def generate_key():
    primes = get_primes_in_range(low, high)
    D = 0
    p = random.choice(primes)
    primes.remove(p)
    q = random.choice(primes)
    if p == q:
        p = random.choice(primes)
        primes.remove(p)
        q = random.choice(primes)
    N = p * q
    phi = (p-1)*(q-1)
    E = random.randrange(1, phi)
    g = are_relatively_prime(E, phi)
    while g != 1:
        E = random.randrange(1, phi)
        g = are_relatively_prime(E, phi)
    for D in range(3, phi, 2):
        if D * E % phi == 1:
            break
    return ((N, E), (N, D))


def power(spisok, b, c):
    return [((x**b) % c)for x in spisok]


def encrypt(message, N, E):
    message_as_numbers = [ord(i) for i in message]
    encrypted_message = power(message_as_numbers, E, N)
    return encrypted_message


def decrypt(encrypted_message, N, D):
    plain = power(encrypted_message, D, N)
    numbers_from_message = [chr(i) for i in plain]
    nosmes = [str(i) for i in numbers_from_message]
    nosmes = "".join(nosmes)
    return nosmes

if __name__ == '__main__':
    print "This program will use RSA Encryption to encrypt any message you input."
    print "Begin by choosing an interval in which the program should search for primes."
    low = int(input("Please enter a lower bound for your prime search: "))
    high = int(input("Please enter an upper bound for your prime search: "))
    (N, E), (N, D) = generate_key()
    print "The encryption keys have been generated."
    message = raw_input("Please enter the message you wish to encrypt: ")
    print "Your message will now be encrypted by the public key: ", (N, E)
    encrypted_message = encrypt(message, N, E)
    print "Your message has been encrypted as: "
    print(encrypt(message, N, E))
    print "Your message will now be decrypted by the private key: ", (N, D)
    decrypted_message = decrypt(encrypted_message, N, D)
    print "Your decrypted message is: "
    print(decrypt(encrypted_message, N, D))

Кажется, это работает, возможно, 9 раз из 10.Однако время от времени при работе в терминале я получаю следующую ошибку:

This program will use RSA Encryption to encrypt any message you input.
Begin by choosing an interval in which the program should search for primes.
Please enter a lower bound for your prime search: 132
Please enter an upper bound for your prime search: 134
The encryption keys have been generated.
Please enter the message you wish to encrypt: hello
Your message will now be encrypted by the public key:  (18769, 16141)
Your message has been encrypted as: 
[18283L, 12834L, 4908L, 4908L, 11027L]
Your message will now be decrypted by the private key:  (18769, 17797)
Traceback (most recent call last):
  File "rsaencrtry.py", line 135, in <module>
    decrypted_message = decrypt(encrypted_message, N, D)
  File "rsaencrtry.py", line 117, in decrypt
    numbers_from_message = [chr(i) for i in plain]
ValueError: chr() arg not in range(256)

Я понимаю, что chr () ищет значение от 0 до 255 (коды символов ASCII), ноЯ не понимаю, почему мой алгоритм возвращает значения за пределами этого диапазона.Кажется, это происходит, когда выбранные простые числа близки друг к другу.

Это проблема с моей функцией расшифровки или с выбором простых чисел?