diff --git a/common.py b/common.py
index 06bf933..b7de648 100644
--- a/common.py
+++ b/common.py
@@ -1,6 +1,7 @@
 # coding=utf-8
 """Misc common utilities.
 """
+import base64
 import copy
 from datetime import timedelta
 import logging
@@ -9,6 +10,7 @@ import threading
 import urllib.parse
 
 import cachetools
+from Crypto.Util import number
 from flask import abort, g, make_response, request
 from granary import as1, as2, microformats2
 import mf2util
@@ -48,6 +50,23 @@ DOMAIN_BLOCKLIST = frozenset((
 CACHE_TIME = timedelta(seconds=60)
 
 
+def base64_to_long(x):
+    """Converts x from URL safe base64 encoding to a long integer.
+
+    Originally from django_salmon.magicsigs. Used in :meth:`User.public_pem`
+    and :meth:`User.private_pem`.
+    """
+    return number.bytes_to_long(base64.urlsafe_b64decode(x))
+
+
+def long_to_base64(x):
+    """Converts x from a long integer to base64 URL safe encoding.
+
+    Originally from django_salmon.magicsigs. Used in :meth:`User.get_or_create`.
+    """
+    return base64.urlsafe_b64encode(number.long_to_bytes(x))
+
+
 def host_url(path_query=None):
   base = request.host_url
   if (util.domain_or_parent_in(request.host, OTHER_DOMAINS) or
diff --git a/models.py b/models.py
index 144208f..e483479 100644
--- a/models.py
+++ b/models.py
@@ -1,5 +1,4 @@
 """Datastore model classes."""
-import base64
 from datetime import timedelta, timezone
 import itertools
 import json
@@ -10,7 +9,6 @@ import urllib.parse
 from arroba.mst import dag_cbor_cid
 from Crypto import Random
 from Crypto.PublicKey import ECC, RSA
-from Crypto.Util import number
 import dag_json
 from flask import g, request
 from google.cloud import ndb
@@ -23,6 +21,7 @@ from oauth_dropins.webutil.util import json_dumps, json_loads
 import requests
 
 import common
+from common import base64_to_long, long_to_base64
 
 # maps string label to Protocol subclass. populated by ProtocolUserMeta.
 # seed with old and upcoming protocols that don't have their own classes (yet).
@@ -65,22 +64,6 @@ def reset_protocol_properties():
         'source_protocol', choices=list(PROTOCOLS.keys()))
 
 
-def base64_to_long(x):
-    """Converts x from URL safe base64 encoding to a long integer.
-
-    Originally from django_salmon.magicsigs.
-    """
-    return number.bytes_to_long(base64.urlsafe_b64decode(x))
-
-
-def long_to_base64(x):
-    """Converts x from a long integer to base64 URL safe encoding.
-
-    Originally from django_salmon.magicsigs.
-    """
-    return base64.urlsafe_b64encode(number.long_to_bytes(x))
-
-
 class User(StringIdModel, metaclass=ProtocolUserMeta):
     """Abstract base class for a Bridgy Fed user.