diff --git a/trezor_agent/gpg/keyring.py b/trezor_agent/gpg/keyring.py
index 9440b0f..427c42c 100644
--- a/trezor_agent/gpg/keyring.py
+++ b/trezor_agent/gpg/keyring.py
@@ -44,11 +44,8 @@ def _recvline(sock):
     return result
 
 
-def _hex(data):
-    return binascii.hexlify(data).upper().decode('ascii')
-
-
-def _unescape(s):
+def unescape(s):
+    """Unescape ASSUAN message."""
     s = bytearray(s)
     i = 0
     while i < len(s):
@@ -60,23 +57,25 @@ def _unescape(s):
     return bytes(s)
 
 
-def _parse_term(s):
+def parse_term(s):
+    """Parse single s-expr term from bytes."""
     size, s = s.split(b':', 1)
     size = int(size)
     return s[:size], s[size:]
 
 
-def _parse(s):
+def parse(s):
+    """Parse full s-expr from bytes."""
     if s.startswith(b'('):
         s = s[1:]
-        name, s = _parse_term(s)
+        name, s = parse_term(s)
         values = [name]
         while not s.startswith(b')'):
-            value, s = _parse(s)
+            value, s = parse(s)
             values.append(value)
         return values, s[1:]
     else:
-        return _parse_term(s)
+        return parse_term(s)
 
 
 def _parse_ecdsa_sig(args):
@@ -86,6 +85,7 @@ def _parse_ecdsa_sig(args):
     return (util.bytes2num(sig_r),
             util.bytes2num(sig_s))
 
+# DSA happens to have the same structure as ECDSA signatures
 _parse_dsa_sig = _parse_ecdsa_sig
 
 
@@ -95,7 +95,8 @@ def _parse_rsa_sig(args):
     return (util.bytes2num(sig_s),)
 
 
-def _parse_sig(sig):
+def parse_sig(sig):
+    """Parse signature integer values from s-expr."""
     label, sig = sig
     assert label == b'sig-val'
     algo_name = sig[0]
@@ -123,23 +124,24 @@ def sign_digest(sock, keygrip, digest):
         assert _communicate(sock, 'OPTION {}'.format(opt)) == b'OK'
 
     assert _communicate(sock, 'SIGKEY {}'.format(keygrip)) == b'OK'
+    hex_digest = binascii.hexlify(digest).upper().decode('ascii')
     assert _communicate(sock, 'SETHASH {} {}'.format(hash_algo,
-                                                     _hex(digest))) == b'OK'
+                                                     hex_digest)) == b'OK'
 
     desc = ('Please+enter+the+passphrase+to+unlock+the+OpenPGP%0A'
             'secret+key,+to+sign+a+new+TREZOR-based+subkey')
     assert _communicate(sock, 'SETKEYDESC {}'.format(desc)) == b'OK'
     assert _communicate(sock, 'PKSIGN') == b'OK'
     line = _recvline(sock).strip()
-    line = _unescape(line)
+    line = unescape(line)
     log.debug('unescaped: %r', line)
     prefix, sig = line.split(b' ', 1)
     if prefix != b'D':
         raise ValueError(prefix)
 
-    sig, leftover = _parse(sig)
+    sig, leftover = parse(sig)
     assert not leftover, leftover
-    return _parse_sig(sig)
+    return parse_sig(sig)
 
 
 def get_keygrip(user_id):
diff --git a/trezor_agent/gpg/tests/test_keyring.py b/trezor_agent/gpg/tests/test_keyring.py
new file mode 100644
index 0000000..b312a5b
--- /dev/null
+++ b/trezor_agent/gpg/tests/test_keyring.py
@@ -0,0 +1,37 @@
+from .. import keyring
+
+
+def test_unescape_short():
+    assert keyring.unescape(b'abc%0AX%0D %25;.-+()') == b'abc\nX\r %;.-+()'
+
+
+def test_unescape_long():
+    escaped = (b'D (7:sig-val(3:dsa(1:r32:\x1d\x15.\x12\xe8h\x19\xd9O\xeb\x06'
+               b'yD?a:/\xae\xdb\xac\x93\xa6\x86\xcbs\xb8\x03\xf1\xcb\x89\xc7'
+               b'\x1f)(1:s32:%25\xb5\x04\x94\xc7\xc4X\xc7\xe0%0D\x08\xbb%0DuN'
+               b'\x9c6}[\xc2=t\x8c\xfdD\x81\xe8\xdd\x86=\xe2\xa9)))')
+    unescaped = (b'D (7:sig-val(3:dsa(1:r32:\x1d\x15.\x12\xe8h\x19\xd9O\xeb'
+                 b'\x06yD?a:/\xae\xdb\xac\x93\xa6\x86\xcbs\xb8\x03\xf1\xcb\x89'
+                 b'\xc7\x1f)(1:s32:%\xb5\x04\x94\xc7\xc4X\xc7\xe0\r\x08\xbb\ru'
+                 b'N\x9c6}[\xc2=t\x8c\xfdD\x81\xe8\xdd\x86=\xe2\xa9)))')
+    assert keyring.unescape(escaped) == unescaped
+
+
+def test_parse_term():
+    assert keyring.parse(b'4:abcdXXX') == (b'abcd', b'XXX')
+
+
+def test_parse_ecdsa():
+    sig, rest = keyring.parse(b'(7:sig-val(5:ecdsa'
+                              b'(1:r2:\x01\x02)(1:s2:\x03\x04)))')
+    values = [[b'r', b'\x01\x02'], [b's', b'\x03\x04']]
+    assert sig == [b'sig-val', [b'ecdsa'] + values]
+    assert rest == b''
+    assert keyring.parse_sig(sig) == (0x102, 0x304)
+
+
+def test_parse_rsa():
+    sig, rest = keyring.parse(b'(7:sig-val(3:rsa(1:s4:\x01\x02\x03\x04)))')
+    assert sig == [b'sig-val', [b'rsa', [b's', b'\x01\x02\x03\x04']]]
+    assert rest == b''
+    assert keyring.parse_sig(sig) == (0x1020304,)