diff --git a/crypto/algo.py b/crypto/algo.py
new file mode 100644
index 0000000..43292fc
--- /dev/null
+++ b/crypto/algo.py
@@ -0,0 +1,62 @@
+from math import gcd
+
+def est_premier(n):
+    if n < 2:
+        return False
+    for i in range(2, int(n**0.5) + 1):
+        if n % i == 0:
+            return False
+    return True
+
+def liste_premier_inf(n):
+    return [i for i in range(2, n+1) if est_premier(i)]
+
+def pgcd(a, b):
+    while b:
+        a, b = b, a % b
+    return a
+
+def cle_publique_possible(a, b):
+    n = a * b
+    return [i for i in range(1, n) if pgcd(i, n) == 1]
+
+def inverse(e, n):
+    t, newt = 0, 1
+    r, newr = n, e
+    while newr != 0:
+        quotient = r // newr
+        t, newt = newt, t - quotient * newt
+        r, newr = newr, r - quotient * newr
+    if r > 1:
+        raise ValueError("L'inverse modulaire n'existe pas")
+    if t < 0:
+        t += n
+    return t
+
+def chaine_en_liste(chaine):
+    return [ord(c) for c in chaine]
+
+def chiffre(e, N, liste):
+    return [pow(x, e, N) for x in liste]
+
+def dechiffre(d, N, liste):
+    return [pow(x, d, N) for x in liste]
+
+def liste_en_chaine(liste):
+    return ''.join(chr(x) for x in liste)
+
+a, b = 61, 53
+N = a * b
+phi = (a - 1) * (b - 1)
+e = 17
+d = inverse(e, phi)
+
+message = "RSA"
+message_code = chaine_en_liste(message)
+message_chiffre = chiffre(e, N, message_code)
+message_dechiffre = dechiffre(d, N, message_chiffre)
+message_final = liste_en_chaine(message_dechiffre)
+
+print("Message initial:", message)
+print("Message chiffré:", message_chiffre)
+print("Message déchiffré:", message_final)