diff --git a/libagent/device/ui.py b/libagent/device/ui.py
index 20c0434..d73d91d 100644
--- a/libagent/device/ui.py
+++ b/libagent/device/ui.py
@@ -4,7 +4,7 @@ import logging
 import os
 import subprocess
 
-from ..gpg import agent
+from .. import util
 
 log = logging.getLogger(__name__)
 
@@ -93,17 +93,17 @@ def interact(title, description, prompt, binary, options):
                          env=os.environ)
     expect(p, [b'OK'])
 
-    title = agent.serialize(title.encode('ascii'))
+    title = util.assuan_serialize(title.encode('ascii'))
     write(p, b'SETTITLE ' + title + b'\n')
     expect(p, [b'OK'])
 
     if description:
-        description = agent.serialize(description.encode('ascii'))
+        description = util.assuan_serialize(description.encode('ascii'))
         write(p, b'SETDESC ' + description + b'\n')
         expect(p, [b'OK'])
 
     if prompt:
-        prompt = agent.serialize(prompt.encode('ascii'))
+        prompt = util.assuan_serialize(prompt.encode('ascii'))
         write(p, b'SETPROMPT ' + prompt + b'\n')
         expect(p, [b'OK'])
 
diff --git a/libagent/gpg/agent.py b/libagent/gpg/agent.py
index c4271e5..1bfad8f 100644
--- a/libagent/gpg/agent.py
+++ b/libagent/gpg/agent.py
@@ -21,25 +21,17 @@ def yield_connections(sock):
         yield conn
 
 
-def serialize(data):
-    """Serialize data according to ASSUAN protocol."""
-    for c in [b'%', b'\n', b'\r']:
-        escaped = '%{:02X}'.format(ord(c)).encode('ascii')
-        data = data.replace(c, escaped)
-    return data
-
-
 def sig_encode(r, s):
     """Serialize ECDSA signature data into GPG S-expression."""
-    r = serialize(util.num2bytes(r, 32))
-    s = serialize(util.num2bytes(s, 32))
+    r = util.assuan_serialize(util.num2bytes(r, 32))
+    s = util.assuan_serialize(util.num2bytes(s, 32))
     return b'(7:sig-val(5:ecdsa(1:r32:' + r + b')(1:s32:' + s + b')))'
 
 
 def _serialize_point(data):
     prefix = '{}:'.format(len(data)).encode('ascii')
     # https://www.gnupg.org/documentation/manuals/assuan/Server-responses.html
-    return b'(5:value' + serialize(prefix + data) + b')'
+    return b'(5:value' + util.assuan_serialize(prefix + data) + b')'
 
 
 def parse_ecdh(line):
diff --git a/libagent/gpg/tests/test_agent.py b/libagent/gpg/tests/test_agent.py
new file mode 100644
index 0000000..2f82522
--- /dev/null
+++ b/libagent/gpg/tests/test_agent.py
@@ -0,0 +1,11 @@
+from .. import agent
+
+
+def test_sig_encode():
+    SIG = (
+        b'(7:sig-val(5:ecdsa(1:r32:\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
+        b'\x00\x00\x00\x00\x0c)(1:s32:\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
+        b'\x00\x00\x00\x00")))')
+    assert agent.sig_encode(12, 34) == SIG
diff --git a/libagent/tests/test_util.py b/libagent/tests/test_util.py
index ead8970..2cef300 100644
--- a/libagent/tests/test_util.py
+++ b/libagent/tests/test_util.py
@@ -115,3 +115,9 @@ def test_memoize():
     assert g(1) == g(1)
     assert g(1) != g(2)
     assert f.mock_calls == [mock.call(1), mock.call(2)]
+
+
+def test_assuan_serialize():
+    assert util.assuan_serialize(b'') == b''
+    assert util.assuan_serialize(b'123\n456') == b'123%0A456'
+    assert util.assuan_serialize(b'\r\n') == b'%0D%0A'
diff --git a/libagent/util.py b/libagent/util.py
index 15c172b..623ddda 100644
--- a/libagent/util.py
+++ b/libagent/util.py
@@ -229,3 +229,11 @@ def which(cmd):
         raise OSError('Cannot find {!r} in $PATH'.format(cmd))
     log.debug('which %r => %r', cmd, full_path)
     return full_path
+
+
+def assuan_serialize(data):
+    """Serialize data according to ASSUAN protocol (for GPG daemon communication)."""
+    for c in [b'%', b'\n', b'\r']:
+        escaped = '%{:02X}'.format(ord(c)).encode('ascii')
+        data = data.replace(c, escaped)
+    return data