diff --git a/taskchampion/src/server/crypto.rs b/taskchampion/src/server/crypto.rs
index b2728acad..978a38fd8 100644
--- a/taskchampion/src/server/crypto.rs
+++ b/taskchampion/src/server/crypto.rs
@@ -317,4 +317,96 @@ mod test {
         let cryptor = Cryptor::new(client_key, &secret).unwrap();
         assert!(cryptor.unseal(sealed).is_err());
     }
+
+    mod externally_valid {
+        // validate data generated by generate-test-data.py.  The intent is to
+        // validate that this format matches the specification by implementing
+        // the specification in a second language
+        use super::*;
+        use pretty_assertions::assert_eq;
+
+        /// The values in generate-test-data.py
+        fn defaults() -> (Uuid, Uuid, Vec<u8>) {
+            (
+                Uuid::parse_str("b0517957-f912-4d49-8330-f612e73030c4").unwrap(),
+                Uuid::parse_str("0666d464-418a-4a08-ad53-6f15c78270cd").unwrap(),
+                b"b4a4e6b7b811eda1dc1a2693ded".to_vec(),
+            )
+        }
+
+        #[test]
+        fn good() {
+            let (version_id, client_key, encryption_secret) = defaults();
+            let sealed = Sealed {
+                version_id,
+                payload: include_bytes!("test-good.data").to_vec(),
+            };
+
+            let cryptor = Cryptor::new(client_key, &Secret(encryption_secret)).unwrap();
+            let unsealed = cryptor.unseal(sealed).unwrap();
+
+            assert_eq!(unsealed.payload, b"SUCCESS");
+            assert_eq!(unsealed.version_id, version_id);
+        }
+
+        #[test]
+        fn bad_version_id() {
+            let (version_id, client_key, encryption_secret) = defaults();
+            let sealed = Sealed {
+                version_id,
+                payload: include_bytes!("test-bad-version-id.data").to_vec(),
+            };
+
+            let cryptor = Cryptor::new(client_key, &Secret(encryption_secret)).unwrap();
+            assert!(cryptor.unseal(sealed).is_err());
+        }
+
+        #[test]
+        fn bad_client_key() {
+            let (version_id, client_key, encryption_secret) = defaults();
+            let sealed = Sealed {
+                version_id,
+                payload: include_bytes!("test-bad-client-key.data").to_vec(),
+            };
+
+            let cryptor = Cryptor::new(client_key, &Secret(encryption_secret)).unwrap();
+            assert!(cryptor.unseal(sealed).is_err());
+        }
+
+        #[test]
+        fn bad_secret() {
+            let (version_id, client_key, encryption_secret) = defaults();
+            let sealed = Sealed {
+                version_id,
+                payload: include_bytes!("test-bad-secret.data").to_vec(),
+            };
+
+            let cryptor = Cryptor::new(client_key, &Secret(encryption_secret)).unwrap();
+            assert!(cryptor.unseal(sealed).is_err());
+        }
+
+        #[test]
+        fn bad_version() {
+            let (version_id, client_key, encryption_secret) = defaults();
+            let sealed = Sealed {
+                version_id,
+                payload: include_bytes!("test-bad-version.data").to_vec(),
+            };
+
+            let cryptor = Cryptor::new(client_key, &Secret(encryption_secret)).unwrap();
+            assert!(cryptor.unseal(sealed).is_err());
+        }
+
+        #[test]
+        fn bad_app_id() {
+            let (version_id, client_key, encryption_secret) = defaults();
+            let sealed = Sealed {
+                version_id,
+                payload: include_bytes!("test-bad-app-id.data").to_vec(),
+            };
+
+            let cryptor = Cryptor::new(client_key, &Secret(encryption_secret)).unwrap();
+            assert!(cryptor.unseal(sealed).is_err());
+        }
+    }
 }
diff --git a/taskchampion/src/server/generate-test-data.py b/taskchampion/src/server/generate-test-data.py
new file mode 100644
index 000000000..366597813
--- /dev/null
+++ b/taskchampion/src/server/generate-test-data.py
@@ -0,0 +1,77 @@
+# This file generates test-encrypted.data.  To run it:
+# - pip install cryptography pbkdf2
+# - python taskchampion/src/server/generate-test-data.py taskchampion/src/server/
+
+import os
+import hashlib
+import pbkdf2
+import secrets
+import sys
+import uuid
+
+from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305
+
+# these values match values used in the rust tests
+client_key = "0666d464-418a-4a08-ad53-6f15c78270cd"
+encryption_secret = b"b4a4e6b7b811eda1dc1a2693ded"
+version_id = "b0517957-f912-4d49-8330-f612e73030c4"
+
+def gen(
+    version_id=version_id, client_key=client_key, encryption_secret=encryption_secret,
+    app_id=1, version=1):
+    # first, generate the encryption key
+    salt = hashlib.sha256(uuid.UUID(client_key).bytes).digest()
+    key = pbkdf2.PBKDF2(
+        encryption_secret,
+        salt,
+        digestmodule=hashlib.sha256,
+        iterations=100000,
+    ).read(32)
+
+    # create a nonce
+    nonce = secrets.token_bytes(12)
+
+    assert len(b"\x01") == 1
+    # create the AAD
+    aad = b''.join([
+        bytes([app_id]),
+        uuid.UUID(version_id).bytes,
+    ])
+
+    # encrypt using AEAD
+    chacha = ChaCha20Poly1305(key)
+    ciphertext = chacha.encrypt(nonce, b"SUCCESS", aad)
+
+    # create the envelope
+    envelope = b''.join([
+        bytes([version]),
+        nonce,
+        ciphertext,
+    ])
+
+    return envelope
+
+
+def main():
+    dir = sys.argv[1]
+
+    with open(os.path.join(dir, 'test-good.data'), "wb") as f:
+        f.write(gen())
+
+    with open(os.path.join(dir, 'test-bad-version-id.data'), "wb") as f:
+        f.write(gen(version_id=uuid.uuid4().hex))
+
+    with open(os.path.join(dir, 'test-bad-client-key.data'), "wb") as f:
+        f.write(gen(client_key=uuid.uuid4().hex))
+
+    with open(os.path.join(dir, 'test-bad-secret.data'), "wb") as f:
+        f.write(gen(encryption_secret=b"xxxxxxxxxxxxxxxxxxxxx"))
+
+    with open(os.path.join(dir, 'test-bad-version.data'), "wb") as f:
+        f.write(gen(version=99))
+
+    with open(os.path.join(dir, 'test-bad-app-id.data'), "wb") as f:
+        f.write(gen(app_id=99))
+
+
+main()
diff --git a/taskchampion/src/server/test-bad-app-id.data b/taskchampion/src/server/test-bad-app-id.data
new file mode 100644
index 000000000..a1c6832a6
--- /dev/null
+++ b/taskchampion/src/server/test-bad-app-id.data
@@ -0,0 +1,2 @@
+
#�$�
+���^~B>n)j�i��1��9�|���~
\ No newline at end of file
diff --git a/taskchampion/src/server/test-bad-client-key.data b/taskchampion/src/server/test-bad-client-key.data
new file mode 100644
index 000000000..bfdd9635e
--- /dev/null
+++ b/taskchampion/src/server/test-bad-client-key.data
@@ -0,0 +1 @@
+
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t;��
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\ No newline at end of file
diff --git a/taskchampion/src/server/test-bad-secret.data b/taskchampion/src/server/test-bad-secret.data
new file mode 100644
index 000000000..696da066f
--- /dev/null
+++ b/taskchampion/src/server/test-bad-secret.data
@@ -0,0 +1 @@
+
/}�dE��dIc�X��-�!V��%�4���d]���}
\ No newline at end of file
diff --git a/taskchampion/src/server/test-bad-version-id.data b/taskchampion/src/server/test-bad-version-id.data
new file mode 100644
index 000000000..2ccd8c638
--- /dev/null
+++ b/taskchampion/src/server/test-bad-version-id.data
@@ -0,0 +1 @@
+
l���a|��@ύS_����z�V9�q�х�)+��
\ No newline at end of file
diff --git a/taskchampion/src/server/test-bad-version.data b/taskchampion/src/server/test-bad-version.data
new file mode 100644
index 000000000..20fed792e
--- /dev/null
+++ b/taskchampion/src/server/test-bad-version.data
@@ -0,0 +1 @@
+c��TH��p>��溦m4��~�1�0P�I��W�
\ No newline at end of file
diff --git a/taskchampion/src/server/test-bad-version_id.data b/taskchampion/src/server/test-bad-version_id.data
new file mode 100644
index 000000000..4a228ec4a
--- /dev/null
+++ b/taskchampion/src/server/test-bad-version_id.data
@@ -0,0 +1,2 @@
+
B�
+��-�3%�j�,*ߺ7꩖Q�K�O��FPZ�
\ No newline at end of file
diff --git a/taskchampion/src/server/test-good.data b/taskchampion/src/server/test-good.data
new file mode 100644
index 000000000..9efec7577
--- /dev/null
+++ b/taskchampion/src/server/test-good.data
@@ -0,0 +1 @@
+
pѿ�ҟ�V����To�"}cT��Y7� ��@�dLT�`�
\ No newline at end of file