diff --git a/libagent/gpg/decode.py b/libagent/gpg/decode.py
index f3b620f..20005fd 100644
--- a/libagent/gpg/decode.py
+++ b/libagent/gpg/decode.py
@@ -63,6 +63,17 @@ def _parse_nist256p1_pubkey(mpi):
         hashfunc=hashlib.sha256)
 
 
+def _parse_nist521p1_pubkey(mpi):
+    prefix, x, y = util.split_bits(mpi, 4, 528, 528)
+    if prefix != 4:
+        raise ValueError('Invalid MPI prefix: {}'.format(prefix))
+    point = ecdsa.ellipticcurve.Point(curve=ecdsa.NIST521p.curve,
+                                      x=x, y=y)
+    return ecdsa.VerifyingKey.from_public_point(
+        point=point, curve=ecdsa.curves.NIST521p,
+        hashfunc=hashlib.sha512)
+
+
 def _parse_ed25519_pubkey(mpi):
     prefix, value = util.split_bits(mpi, 8, 256)
     if prefix != 0x40:
@@ -73,6 +84,8 @@ def _parse_ed25519_pubkey(mpi):
 SUPPORTED_CURVES = {
     b'\x2A\x86\x48\xCE\x3D\x03\x01\x07':
         (_parse_nist256p1_pubkey, protocol.keygrip_nist256),
+    b'\x2B\x81\x04\x00\x23':
+        (_parse_nist521p1_pubkey, protocol.keygrip_nist521),
     b'\x2B\x06\x01\x04\x01\xDA\x47\x0F\x01':
         (_parse_ed25519_pubkey, protocol.keygrip_ed25519),
     b'\x2B\x06\x01\x04\x01\x97\x55\x01\x05\x01':
diff --git a/libagent/gpg/protocol.py b/libagent/gpg/protocol.py
index 68bb7f8..1786973 100644
--- a/libagent/gpg/protocol.py
+++ b/libagent/gpg/protocol.py
@@ -101,6 +101,7 @@ def _compute_keygrip(params):
         exp = '{}:{}{}:'.format(len(name), name, len(value))
         parts.append(b'(' + exp.encode('ascii') + value + b')')
 
+    log.debug('keygrip parts: %s', parts)
     return hashlib.sha1(b''.join(parts)).digest()
 
 
@@ -122,6 +123,23 @@ def keygrip_nist256(vk):
     ])
 
 
+def keygrip_nist521(vk):
+    """Compute keygrip for NIST521 curve public keys."""
+    curve = vk.curve.curve
+    gen = vk.curve.generator
+    g = (4 << 1200) | (gen.x() << 600) | gen.y()
+    point = vk.pubkey.point
+    q = (4 << 1200) | (point.x() << 600) | point.y()
+    return _compute_keygrip([
+        ['p', util.num2bytes(curve.p(), size=66)],
+        ['a', util.num2bytes(curve.a() % curve.p(), size=66)],
+        ['b', util.num2bytes(curve.b() % curve.p(), size=66)],
+        ['g', util.num2bytes(g, size=160)],
+        ['n', util.num2bytes(vk.curve.order, size=66)],
+        ['q', util.num2bytes(q, size=160)],
+    ])
+
+
 def keygrip_ed25519(vk):
     """Compute keygrip for Ed25519 public keys."""
     # pylint: disable=line-too-long