diff --git a/src/allmydata/crypto/ed25519.py b/src/allmydata/crypto/ed25519.py
index b8404dec0..e05c92020 100644
--- a/src/allmydata/crypto/ed25519.py
+++ b/src/allmydata/crypto/ed25519.py
@@ -31,10 +31,9 @@ from cryptography.hazmat.primitives.serialization import (
     PublicFormat,
 )
 
-from allmydata.crypto import (
-    remove_prefix,
-    BadSignature,
-)
+from allmydata.crypto.util import remove_prefix
+from allmydata.crypto.error import BadSignature
+
 from allmydata.util.base32 import (
     a2b,
     b2a,
diff --git a/src/allmydata/crypto/error.py b/src/allmydata/crypto/error.py
new file mode 100644
index 000000000..62c0b3e5b
--- /dev/null
+++ b/src/allmydata/crypto/error.py
@@ -0,0 +1,15 @@
+"""
+Exceptions raise by allmydata.crypto.* modules
+"""
+
+
+class BadSignature(Exception):
+    """
+    An alleged signature did not match
+    """
+
+
+class BadPrefixError(Exception):
+    """
+    A key did not start with the required prefix
+    """
diff --git a/src/allmydata/crypto/rsa.py b/src/allmydata/crypto/rsa.py
index 611da1649..25a361640 100644
--- a/src/allmydata/crypto/rsa.py
+++ b/src/allmydata/crypto/rsa.py
@@ -5,7 +5,7 @@ from cryptography.hazmat.primitives.asymmetric import rsa, padding
 from cryptography.hazmat.primitives.serialization import load_der_private_key, load_der_public_key, \
     Encoding, PrivateFormat, PublicFormat, NoEncryption
 
-from allmydata.crypto import BadSignature
+from allmydata.crypto.error import BadSignature
 
 
 """
diff --git a/src/allmydata/crypto/util.py b/src/allmydata/crypto/util.py
index 571f55387..7e4ebb92f 100644
--- a/src/allmydata/crypto/util.py
+++ b/src/allmydata/crypto/util.py
@@ -2,17 +2,7 @@
 Utilities used by allmydata.crypto modules
 """
 
-
-class BadSignature(Exception):
-    """
-    An alleged signature did not match
-    """
-
-
-class BadPrefixError(Exception):
-    """
-    A key did not start with the required prefix
-    """
+from allmydata.crypto.error import BadPrefixError
 
 
 def remove_prefix(s_bytes, prefix):
diff --git a/src/allmydata/introducer/client.py b/src/allmydata/introducer/client.py
index f6047dbff..225ec1abc 100644
--- a/src/allmydata/introducer/client.py
+++ b/src/allmydata/introducer/client.py
@@ -9,7 +9,7 @@ from allmydata.introducer.common import sign_to_foolscap, unsign_from_foolscap,\
      get_tubid_string_from_ann
 from allmydata.util import log, yamlutil, connection_status
 from allmydata.util.rrefutil import add_version_to_remote_reference
-from allmydata.crypto import BadSignature
+from allmydata.crypto.error import BadSignature
 from allmydata.util.assertutil import precondition
 
 class InvalidCacheError(Exception):
diff --git a/src/allmydata/mutable/servermap.py b/src/allmydata/mutable/servermap.py
index a50db6e78..8dba6d8b5 100644
--- a/src/allmydata/mutable/servermap.py
+++ b/src/allmydata/mutable/servermap.py
@@ -8,7 +8,7 @@ from twisted.internet import defer
 from twisted.python import failure
 from foolscap.api import DeadReferenceError, RemoteException, eventually, \
                          fireEventually
-from allmydata.crypto import BadSignature
+from allmydata.crypto.error import BadSignature
 from allmydata.crypto import rsa
 from allmydata.util import base32, hashutil, log, deferredutil
 from allmydata.util.dictutil import DictOfSets