diff --git a/synchro_orleans/data/management/commands/email_new_invoices.py b/synchro_orleans/data/management/commands/email_new_invoices.py
index 94fb660..4e64642 100644
--- a/synchro_orleans/data/management/commands/email_new_invoices.py
+++ b/synchro_orleans/data/management/commands/email_new_invoices.py
@@ -5,6 +5,7 @@ import os
 import requests
 import logging
 from hashlib import sha256
+import hmac
 
 from django.core.management.base import BaseCommand, CommandError
 from django.conf import settings
@@ -31,9 +32,10 @@ class Command(BaseCommand):
     email_subject = 'Nouvelle facture'
     email_template = 'invoice_mail.txt'
     email_from = settings.DEFAULT_FROM_EMAIL
+    secret = settings.INVOICE_HASHING_SECRET
 
     def get_invoice_hash(self, *args):
-        hash = sha256(''.join(map(lambda s: str(s), args)))
+        hash = hmac.HMAC(self.secret, digestmod=sha256, msg=''.join(map(lambda s: str(s), args)))
         return hash.hexdigest()[:8]
 
 
diff --git a/synchro_orleans/settings.py b/synchro_orleans/settings.py
index 2bf70bd..5254f5b 100644
--- a/synchro_orleans/settings.py
+++ b/synchro_orleans/settings.py
@@ -169,6 +169,8 @@ EMAILING_APIKEY = os.environ.get('EMAILING_APIKEY', '12345')
 
 INVOICE_VIEW_URL_BASE = PORTAIL_CITOYEN_URL + '/facture/simple/tipi'
 
+INVOICE_HASHING_SECRET = '12345'
+
 IDP_USER_INFO_URL = '%s/userinfo' % IDP_URL
 
 try: