Как дешифровать текст?

Наслаждайтесь :)

Единственное, нужно передовать ключ. В роли ключа здесь выступает набор из 624 целых чисел в диапазоне от 0 до 4294967294. Они используются для составления матрицы Мерсенна, по которой, в последствии, прогнозируются случайные числа, используемые в шифровании.

Ваш алгоритм шифрования я не менял, только добавил дешифровку.

import random, time 

'''
 ------------------------------ ENCODE ------------------------------
'''

class Encoder():
    def __init__(self):  
        self.key = []

    def castom_shuffle(self, lst): 
        for i in range(len(lst)-1, 0, -1):   
            j = random.randint(0, i) 
            lst[i], lst[j] = lst[j], lst[i]      

    def encode(self, text):  
        if not text:
            raise ValueError("Unable to encrypt blank text")

        s = ''.join(e for e in text if e.isalnum()) 
        s = [s[i:i+5][::-1] for i in range(0, len(s), 5)]     

        for i in range(624): 
            self.key.append(random.getrandbits(32)) 

        self.castom_shuffle(s)      
        return ' '.join(s), self.key


'''
 ------------------------------ DECODE ------------------------------
'''
class Decoder: 
    def __init__(self, key):
        self.counter = 0
        self.mt = []
        self.state = False

        for i in key:
            self.submit(i)

    def decode(self,text):
        s = text.split()
        self.predict_shuffle(s) 
        return ''.join([i[::-1] for i in s]) 

    def submit(self, num):
        if self.state:
            raise ValueError("Already got enough bits")

        bits = self._to_bitarray(num)

        assert (all([x == 0 or x == 1 for x in bits]))
        self.counter += 1
        self.mt.append(self._harden_inverse(bits))
        if self.counter == 624:
            self._regen()
            self.state = True

    def _predict_32(self):
        if not self.state:
            raise ValueError("Didn't recieve enough bits to predict")

        if self.counter >= 624:
            self._regen()
        self.counter += 1

        return self._harden(self.mt[self.counter - 1])

    def predict_getrandbits(self, k):
        if not self.state:
            raise ValueError("Didn't recieve enough bits to predict")

        if k == 0:
            return 0
        words = (k - 1) // 32 + 1
        res = []
        for i in range(words):
            r = self._predict_32()
            if k < 32:
                r = [0] * (32 - k) + r[:k]
            res = r + res
            k -= 32
        return self._to_int(res)

    def predict_randbelow(self, n):
        k = n.bit_length()
        r = self.predict_getrandbits(k)
        while r >= n:
            r = self.predict_getrandbits(k)
        return r

    def predict_randrange(self, start, stop=None, step=1, _int=int): 
        istart = _int(start)
        if istart != start:
            raise ValueError("non-integer arg 1 for randrange()")
        if stop is None:
            if istart > 0:
                return self.predict_randbelow(istart)
            raise ValueError("empty range for randrange()")

        istop = _int(stop)
        if istop != stop:
            raise ValueError("non-integer stop for randrange()")
        width = istop - istart
        if step == 1 and width > 0:
            return istart + self.predict_randbelow(width)
        if step == 1:
            raise ValueError("empty range for randrange() (%d,%d, %d)" % (istart, istop, width))

        istep = _int(step)
        if istep != step:
            raise ValueError("non-integer step for randrange()")
        if istep > 0:
            n = (width + istep - 1) // istep
        elif istep < 0:
            n = (width + istep + 1) // istep
        else:
            raise ValueError("zero step for randrange()")

        if n <= 0:
            raise ValueError("empty range for randrange()")

        return istart + istep * self.predict_randbelow(n)

    def predict_randint(self, a, b):
        return self.predict_randrange(a, b + 1) 

    def predict_shuffle(self, seq):
        rr = [self.predict_randint(0, i) for i in range(len(seq)-1, 0, -1)]
        rr.reverse()
        for i in range(1,len(seq)):   
            j = rr[i-1]  
            seq[i], seq[j] = seq[j], seq[i] 

    def _to_bitarray(self, num):
        k = [int(x) for x in bin(num)[2:]]
        return [0] * (32 - len(k)) + k

    def _to_int(self, bits):
        return int("".join(str(i) for i in bits), 2)

    def _or_nums(self, a, b):
        if len(a) < 32:
            a = [0] * (32 - len(a)) + a
        if len(b) < 32:
            b = [0] * (32 - len(b)) + b

        return [x[0] | x[1] for x in zip(a, b)]

    def _xor_nums(self, a, b):
        if len(a) < 32:
            a = [0] * (32 - len(a)) + a
        if len(b) < 32:
            b = [0] * (32 - len(b)) + b

        return [x[0] ^ x[1] for x in zip(a, b)]

    def _and_nums(self, a, b):
        if len(a) < 32:
            a = [0] * (32 - len(a)) + a
        if len(b) < 32:
            b = [0] * (32 - len(b)) + b

        return [x[0] & x[1] for x in zip(a, b)]

    def _decode_harden_midop(self, enc, and_arr, shift): 
        NEW = 0
        XOR = 1
        OK = 2
        work = []
        for i in range(32):
            work.append((NEW, enc[i]))
        changed = True
        while changed:
            changed = False
            for i in range(32):
                status = work[i][0]
                data = work[i][1]
                if i >= 32 - shift and status == NEW:
                    work[i] = (OK, data)
                    changed = True
                elif i < 32 - shift and status == NEW:
                    if and_arr[i] == 0:
                        work[i] = (OK, data)
                        changed = True
                    else:
                        work[i] = (XOR, data)
                        changed = True
                elif status == XOR:
                    i_other = i + shift
                    if work[i_other][0] == OK:
                        work[i] = (OK, data ^ work[i_other][1])
                        changed = True

        return [x[1] for x in work]

    def _harden(self, bits):
        bits = self._xor_nums(bits, bits[:-11])
        bits = self._xor_nums(bits, self._and_nums(bits[7:] + [0] * 7, self._to_bitarray(0x9d2c5680)))
        bits = self._xor_nums(bits, self._and_nums(bits[15:] + [0] * 15, self._to_bitarray(0xefc60000)))
        bits = self._xor_nums(bits, bits[:-18])
        return bits

    def _harden_inverse(self, bits):
        bits = self._xor_nums(bits, bits[:-18])
        bits = self._decode_harden_midop(bits, self._to_bitarray(0xefc60000), 15)
        bits = self._decode_harden_midop(bits, self._to_bitarray(0x9d2c5680), 7)
        bits = self._xor_nums(bits, [0] * 11 + bits[:11] + [0] * 10)
        bits = self._xor_nums(bits, bits[11:21])

        return bits

    def _regen(self):
        N = 624
        M = 397
        MATRIX_A = 0x9908b0df
        LOWER_MASK = 0x7fffffff
        UPPER_MASK = 0x80000000
        mag01 = [self._to_bitarray(0), self._to_bitarray(MATRIX_A)]

        l_bits = self._to_bitarray(LOWER_MASK)
        u_bits = self._to_bitarray(UPPER_MASK)

        for kk in range(0, N - M):
            y = self._or_nums(self._and_nums(self.mt[kk], u_bits), self._and_nums(self.mt[kk + 1], l_bits))
            self.mt[kk] = self._xor_nums(self._xor_nums(self.mt[kk + M], y[:-1]), mag01[y[-1] & 1])

        for kk in range(N - M - 1, N - 1):
            y = self._or_nums(self._and_nums(self.mt[kk], u_bits), self._and_nums(self.mt[kk + 1], l_bits))
            self.mt[kk] = self._xor_nums(self._xor_nums(self.mt[kk + (M - N)], y[:-1]), mag01[y[-1] & 1])

        y = self._or_nums(self._and_nums(self.mt[N - 1], u_bits), self._and_nums(self.mt[0], l_bits))
        self.mt[N - 1] = self._xor_nums(self._xor_nums(self.mt[M - 1], y[:-1]), mag01[y[-1] & 1])

        self.counter = 0


enc = Encoder()
enc_text, key = enc.encode('случайности не случайны')

dec = Decoder(key)
print(dec.decode(enc_text))