diff --git a/addons/payment_authorize/models/payment.py b/addons/payment_authorize/models/payment.py
index f77504d738e..0e97d630c69 100644
--- a/addons/payment_authorize/models/payment.py
+++ b/addons/payment_authorize/models/payment.py
@@ -24,6 +24,7 @@ class PaymentAcquirerAuthorize(models.Model):
     provider = fields.Selection(selection_add=[('authorize', 'Authorize.Net')])
     authorize_login = fields.Char(string='API Login Id', required_if_provider='authorize', groups='base.group_user')
     authorize_transaction_key = fields.Char(string='API Transaction Key', required_if_provider='authorize', groups='base.group_user')
+    authorize_signature_key = fields.Char(string='API Signature Key', groups='base.group_user', compute="_compute_auth_signature_key", inverse="_inverse_auth_signature_key")
 
     def _get_feature_support(self):
         """Get advanced feature support by provider.
@@ -41,6 +42,16 @@ class PaymentAcquirerAuthorize(models.Model):
         res['tokenize'].append('authorize')
         return res
 
+    def _compute_auth_signature_key(self):
+        ICP = self.env['ir.config_parameter'].sudo()
+        for acquirer in self.filtered(lambda a: a.provider == 'authorize'):
+            acquirer.authorize_signature_key = ICP.get_param('payment_authorize.signature_key_%s' % acquirer.id)
+
+    def _inverse_auth_signature_key(self):
+        ICP = self.env['ir.config_parameter'].sudo()
+        for acquirer in self.filtered(lambda a: a.provider == 'authorize'):
+            ICP.set_param('payment_authorize.signature_key_%s' % acquirer.id, acquirer.authorize_signature_key)
+
     def _get_authorize_urls(self, environment):
         """ Authorize URLs """
         if environment == 'prod':
@@ -56,12 +67,24 @@ class PaymentAcquirerAuthorize(models.Model):
             values['x_amount'],
             values['x_currency_code']])
 
-        # [BACKWARD COMPATIBILITY] Check that the merchant did update his transaction
-        # key to signature key (end of MD5 support from Authorize.net)
+        # [BACKWARD COMPATIBILITY, 2nd edition]
         # The signature key is now '128-character hexadecimal format', while the
         # transaction key was only 16-character.
-        if len(values['x_trans_key']) == 128:
+        # One of 2 things should have happened:
+        # 1/ the Transaction Key has been replaced with the Signature Key value (patch from March 2019)
+        #       => Use that to sign, but server-to-server won't work since it uses transaction key
+        #          as its credentials
+        # 2/ the Signature key is a new field (patch from July 2019)
+        #       => Use that field for the signature
+
+        # FORWARD-PORT NOTE: be careful, hexadecimal decoding in python 3 is done by using bytes.fromhex(str)
+        # (P2) self.authorize_signature_key.decode("hex") ==> (P3) bytes.fromhex(self.authorize_signature_key)
+        # FORWARD-PORT NOTE NUMERO DOS: forward part to saas-12.4 but no further
+        if len(values['x_trans_key']) == 128 and not self.authorize_signature_key:
+            self.authorize_signature_key = values['x_trans_key'] # store in the correct field
             return hmac.new(values['x_trans_key'].decode("hex"), data, hashlib.sha512).hexdigest().upper()
+        elif self.authorize_signature_key:
+            return hmac.new(self.authorize_signature_key.decode("hex"), data, hashlib.sha512).hexdigest().upper()
         else:
             return hmac.new(str(values['x_trans_key']), data, hashlib.md5).hexdigest()
 
diff --git a/addons/payment_authorize/views/payment_views.xml b/addons/payment_authorize/views/payment_views.xml
index 7a957e41442..b3f3ed8e535 100644
--- a/addons/payment_authorize/views/payment_views.xml
+++ b/addons/payment_authorize/views/payment_views.xml
@@ -9,6 +9,7 @@
                     <group attrs="{'invisible': [('provider', '!=', 'authorize')]}">
                         <field name="authorize_login"/>
                         <field name="authorize_transaction_key" password="True"/>
+                        <field name="authorize_signature_key" password="True"/>
                         <a colspan="2" href="https://www.odoo.com/documentation/user/online/ecommerce/shopper_experience/authorize.html" target="_blank">How to get paid with Authorize.Net</a>
                     </group>
                 </xpath>