diff --git a/snappass/main.py b/snappass/main.py
index da202596..a05e1382 100644
--- a/snappass/main.py
+++ b/snappass/main.py
@@ -1,4 +1,5 @@
 import os
+import re
 import sys
 import uuid
 
@@ -54,6 +55,11 @@ def get_locale():
                    'hour': 3600}
 DEFAULT_API_TTL = 1209600
 MAX_TTL = DEFAULT_API_TTL
+STORAGE_KEY_PATTERN = re.compile(r'^' + re.escape(REDIS_PREFIX) + r'[0-9a-f]{32}$')
+
+
+def is_valid_storage_key(storage_key):
+    return bool(STORAGE_KEY_PATTERN.fullmatch(storage_key))
 
 
 def check_redis_alive(fn):
@@ -160,6 +166,9 @@ def get_password(token):
     If not, the password is simply returned as is.
     """
     storage_key, decryption_key = parse_token(token)
+    if not is_valid_storage_key(storage_key):
+        return None
+
     password = redis_client.get(storage_key)
     redis_client.delete(storage_key)
 
@@ -173,7 +182,10 @@ def get_password(token):
 
 @check_redis_alive
 def password_exists(token):
-    storage_key, decryption_key = parse_token(token)
+    storage_key, _ = parse_token(token)
+    if not is_valid_storage_key(storage_key):
+        return False
+
     return redis_client.exists(storage_key)
 
 
diff --git a/tests.py b/tests.py
index b4b089e9..e01a2330 100644
--- a/tests.py
+++ b/tests.py
@@ -59,11 +59,21 @@ def test_encryption_key_is_returned(self):
 
     def test_unencrypted_passwords_still_work(self):
         unencrypted_password = "trustevery1"
-        storage_key = uuid.uuid4().hex
+        storage_key = snappass.REDIS_PREFIX + uuid.uuid4().hex
         snappass.redis_client.setex(storage_key, 30, unencrypted_password)
         retrieved_password = snappass.get_password(storage_key)
         self.assertEqual(unencrypted_password, retrieved_password)
 
+    def test_get_password_rejects_non_snappass_storage_key(self):
+        snappass.redis_client.setex("session:42", 30, "sensitive-data")
+        retrieved_password = snappass.get_password("session:42")
+        self.assertIsNone(retrieved_password)
+        self.assertEqual("sensitive-data", snappass.redis_client.get("session:42").decode('utf-8'))
+
+    def test_password_exists_rejects_non_snappass_storage_key(self):
+        snappass.redis_client.setex("session:42", 30, "sensitive-data")
+        self.assertFalse(snappass.password_exists("session:42"))
+
     def test_password_is_decoded(self):
         password = "correct horse battery staple"
         key = snappass.set_password(password, 30)
@@ -314,6 +324,11 @@ def test_check_password_api_v2_bad_keys(self):
         rvc = self.app.head('/api/v2/passwords/' + quote(key[::-1]))
         self.assertEqual(rvc.status_code, 404)
 
+    def test_check_password_api_v2_non_snappass_keys(self):
+        snappass.redis_client.setex("session:42", 30, "sensitive-data")
+        rvc = self.app.head('/api/v2/passwords/' + quote("session:42"))
+        self.assertEqual(rvc.status_code, 404)
+
     def test_retrieve_password_api_v2(self):
         password = 'my name is my passport. verify me.'
         rv = self.app.post(
@@ -352,6 +367,12 @@ def test_retrieve_password_api_v2_bad_keys(self):
         bad_token = invalid_params[0]
         self.assertEqual(bad_token['name'], 'token')
 
+    def test_retrieve_password_api_v2_non_snappass_keys(self):
+        snappass.redis_client.setex("session:42", 30, "sensitive-data")
+        rvc = self.app.get('/api/v2/passwords/' + quote("session:42"))
+        self.assertEqual(rvc.status_code, 404)
+        self.assertEqual("sensitive-data", snappass.redis_client.get("session:42").decode('utf-8'))
+
 
 if __name__ == '__main__':
     unittest.main()