First commit

Cryptotools/Utils/utils.py

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+#!/usr/bin/env python3
+
+def gcd(a, b):
+    """
+        This function calculate the GCD (Greatest Common Divisor of the number a of b
+        Args:
+            a (Integer): the number a
+            b (integer): the number b
+
+        Return:
+            the GCD 
+    """
+
+    if b == 0:
+        return a
+    return gcd(b, a%b)
+
+def egcd(a, b):
+    """
+        This function compute the Extended Euclidean algorithm
+        https://user.eng.umd.edu/~danadach/Cryptography_20/ExtEuclAlg.pdf
+        https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm
+
+        Args:
+            a (Integer): the number a
+            b (Integer): the number b
+    """
+    if a == 0:
+        return b, 0, 1
+    gcd, x1, y1 = egcd(b % a, a)
+    x = y1 - (b // a) * x1
+    y = x1
+    return gcd, x, y
+