diff --git a/swh/model/hashutil.py b/swh/model/hashutil.py
--- a/swh/model/hashutil.py
+++ b/swh/model/hashutil.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2015  The Software Heritage developers
+# Copyright (C) 2015-2017  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -6,9 +6,10 @@
 import binascii
 import functools
 import hashlib
-from io import BytesIO
 import os
 
+from io import BytesIO
+
 # supported hashing algorithms
 ALGORITHMS = set(['sha1', 'sha256', 'sha1_git'])
 
@@ -64,7 +65,7 @@
         ValueError if algo is unknown, or length is missing for a git-specific
         hash.
     """
-    if algo not in ALGORITHMS:
+    if algo not in ALGORITHMS and ':' not in algo:
         raise ValueError('Unexpected hashing algorithm %s, '
                          'expected one of %s' %
                          (algo, ', '.join(sorted(ALGORITHMS))))
@@ -75,6 +76,11 @@
             raise ValueError('Missing length for git hashing algorithm')
         base_algo = algo[:-4]
         h = _new_git_hash(base_algo, 'blob', length)
+    elif ':' in algo:   # variable length hashing algorithms
+        _algo = algo.split(':')
+        base_algo = _algo[0]
+        variable_length = int(_algo[1])
+        h = hashlib.new('%s%s' % (base_algo, variable_length))
     else:
         h = hashlib.new(algo)
 
diff --git a/swh/model/tests/test_hashutil.py b/swh/model/tests/test_hashutil.py
--- a/swh/model/tests/test_hashutil.py
+++ b/swh/model/tests/test_hashutil.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2015  The Software Heritage developers
+# Copyright (C) 2015-2017  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -8,6 +8,7 @@
 import unittest
 
 from nose.tools import istest
+from unittest.mock import patch
 
 from swh.model import hashutil
 
@@ -110,3 +111,31 @@
             hash = self.checksums[type]
             self.assertEquals(hashutil.hash_to_bytes(hex), hash)
             self.assertEquals(hashutil.hash_to_bytes(hash), hash)
+
+    @istest
+    def new_hash_unsupported_hashing_algorithm(self):
+        try:
+            hashutil._new_hash('blake2:10')
+        except ValueError as e:
+            self.assertEquals(str(e),
+                              'unsupported hash type blake210')
+
+    @patch('swh.model.hashutil.hashlib')
+    @istest
+    def new_hash_blake2b(self, mock_hashlib):
+        mock_hashlib.new.return_value = 'some-hashlib-object'
+
+        h = hashutil._new_hash('blake2b:512')
+
+        self.assertEquals(h, 'some-hashlib-object')
+        mock_hashlib.new.assert_called_with('blake2b512')
+
+    @patch('swh.model.hashutil.hashlib')
+    @istest
+    def new_hash_blake2s(self, mock_hashlib):
+        mock_hashlib.new.return_value = 'some-hashlib-object'
+
+        h = hashutil._new_hash('blake2s:256')
+
+        self.assertEquals(h, 'some-hashlib-object')
+        mock_hashlib.new.assert_called_with('blake2s256')