[IMP] web: upgrade the cache to use SHA2 over SHA1

SHA-1 is a cryptographic hash function that have weaknesses known since
2005, it has been deprecated by the NIST [1] about 10 years ago in 2011
and Google [2] have been able to perform a collision attack in 2017.

We use SHA-1 in order to generate unique URL for resources that can be
cached by the browser: assets bundle, translations, qweb templates and
qweb images.

Although practical attacks still requires quite a lot of computational
resources, it is time to upgrade SHA-1 to SHA-2.

We have selected the SHA-512/256 variant of the SHA-2 algorithm as
replacement for SHA-1 for the following reasons:

* On 64 bits platform, SHA-512 is the fastest SHA-2 variant, it is only
  ~1.5x slower than SHA-1. [3]
* Keeping only the 256 foremost bits protects against both collision
  attacks and length extension attacks.
* The hexadecimal digest is only 24 chars longer than SHA-1 which is
  nice to have somewhat short URLs.

We have not used SHA-3 because:

* At the moment of writing, it is too slow (~3x slower than SHA-1) [3]
* It is not guaranteed to be available with the Python 3.5 `hashlib`
  module.
* One of the author of SHA-3 is Belgian.

[1] https://csrc.nist.gov/projects/hash-functions/nist-policy-on-hash-functions
[2] https://shattered.io/
[3] http://bench.cr.yp.to/results-hash.html
[4] http://www.commitstrip.com/en/2017/02/27/the-sha-1-alternative/

5 files changed, 7 insertions, 7 deletions

diff --git a/addons/http_routing/models/ir_http.py b/addons/http_routing/models/ir_http.py
index 8ed7527232c..ae72d2d04e2 100644
--- a/addons/http_routing/models/ir_http.py
+++ b/addons/http_routing/models/ir_http.py
@@ -265,7 +265,7 @@ class IrHttp(models.AbstractModel):
         session_info.update({
             'translationURL': '/website/translations/',
             'cache_hashes': {
-                'translations': hashlib.sha1(json.dumps(translation_cache, sort_keys=True).encode()).hexdigest(),
+                'translations': hashlib.sha512(json.dumps(translation_cache, sort_keys=True).encode()).hexdigest()[:64],  # sha512/256
             },
         })
         return session_info
diff --git a/addons/web/controllers/main.py b/addons/web/controllers/main.py
index 40f351e7f78..b2132850d08 100644
--- a/addons/web/controllers/main.py
+++ b/addons/web/controllers/main.py
@@ -567,7 +567,7 @@ class HomeStaticTemplateHelpers(object):
         :returns: (concatenation_result, checksum)
         :rtype: (bytes, str)
         """
-        checksum = hashlib.new('sha1')
+        checksum = hashlib.new('sha512')  # sha512/256
         if not file_dict:
             return b'', checksum.hexdigest()
 
@@ -586,7 +586,7 @@ class HomeStaticTemplateHelpers(object):
             for template in addon.values():
                 root.append(template)
 
-        return etree.tostring(root, encoding='utf-8') if root is not None else b'', checksum.hexdigest()
+        return etree.tostring(root, encoding='utf-8') if root is not None else b'', checksum.hexdigest()[:64]
 
     def _get_qweb_templates(self):
         """One and only entry point that gets and evaluates static qweb templates
diff --git a/addons/web/models/ir_http.py b/addons/web/models/ir_http.py
index f5a9f922abf..65ae8073326 100644
--- a/addons/web/models/ir_http.py
+++ b/addons/web/models/ir_http.py
@@ -62,9 +62,9 @@ class Http(models.AbstractModel):
             "show_effect": True,
             "display_switch_company_menu": user.has_group('base.group_multi_company') and len(user.company_ids) > 1,
             "cache_hashes": {
-                "load_menus": hashlib.sha1(menu_json_utf8).hexdigest(),
+                "load_menus": hashlib.sha512(menu_json_utf8).hexdigest()[:64],  # sha512/256
                 "qweb": qweb_checksum,
-                "translations": hashlib.sha1(translations_json_utf8).hexdigest(),
+                "translations": hashlib.sha512(translations_json_utf8).hexdigest()[:64],  # sha512/256
             },
         }
 
diff --git a/addons/web/models/ir_qweb.py b/addons/web/models/ir_qweb.py
index 1083916ebf5..6776dbbff14 100644
--- a/addons/web/models/ir_qweb.py
+++ b/addons/web/models/ir_qweb.py
@@ -43,7 +43,7 @@ class Image(models.AbstractModel):
             if max_width or max_height:
                 max_size = '%sx%s' % (max_width, max_height)
 
-        sha = hashlib.sha1(str(getattr(record, '__last_update')).encode('utf-8')).hexdigest()[0:7]
+        sha = hashlib.sha512(str(getattr(record, '__last_update')).encode('utf-8')).hexdigest()[:7]
         max_size = '' if max_size is None else '/%s' % max_size
 
         if options.get('filename-field') and getattr(record, options['filename-field'], None):
diff --git a/addons/website/models/website.py b/addons/website/models/website.py
index 3902f5dae8a..56bdf09e972 100644
--- a/addons/website/models/website.py
+++ b/addons/website/models/website.py
@@ -787,7 +787,7 @@ class Website(models.Model):
     def image_url(self, record, field, size=None):
         """ Returns a local url that points to the image field of a given browse record. """
         sudo_record = record.sudo()
-        sha = hashlib.sha1(str(getattr(sudo_record, '__last_update')).encode('utf-8')).hexdigest()[0:7]
+        sha = hashlib.sha512(str(getattr(sudo_record, '__last_update')).encode('utf-8')).hexdigest()[:7]
         size = '' if size is None else '/%s' % size
         return '/web/image/%s/%s/%s%s?unique=%s' % (record._name, record.id, field, size, sha)