Mind your Ps and Qs

mind_your_ps_and_qs/sol.py

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+#!/usr/bin/python3
+import math
+
+def totient(p, q):
+    tot, rem = divmod((p-1) * (q-1), math.gcd(p-1, q-1))
+    if rem != 0:
+        raise Exception("totient calc failed")
+    return tot
+
+def egcd(a, b):
+    x0, x1, y0, y1 = 0, 1, 1, 0
+    while a != 0:
+        (q, a), b = divmod(b, a), a
+        y0, y1 = y1, y0 - q * y1
+        x0, x1 = x1, x0 - q * x1
+    return b, x0, x1
+
+# https://en.wikibooks.org/wiki/Algorithm_Implementation/Mathematics/Extended_Euclidean_algorithm
+def mod_inv(d, lambda_n):
+    g, x, _ = egcd(d, lambda_n)
+    if g != 1:
+        raise Exception("gcd(d, lambda_n != !")
+    return x % lambda_n
+
+def rsa(text, key, n):
+    return pow(text, key, n)
+
+with open("values", 'r') as f:
+    lines = f.readlines()
+
+    C = int(lines[1][3:])
+    n = int(lines[2][3:])
+    e = int(lines[3][3:])
+    p = int(lines[4][3:])
+    q = int(lines[5][3:])
+
+    if p*q == n:
+        print("factoring correct")
+    else:
+        print("factoring incorrect")
+
+    lambda_n = totient(p, q)
+
+    d = mod_inv(e, lambda_n)
+    #d = pow(d, -1, lambda_n)
+
+    res = rsa(C, d, n)
+
+    text = ''
+    while (char := (res % 256)) != 0:
+        text = chr(char) + text;
+        res >>= 8
+
+    print(text)
+