From 9c641fed9171311bc559740499d0dfaa49bcbaa5 Mon Sep 17 00:00:00 2001
From: brenzi <brenzi@users.noreply.github.com>
Date: Sat, 3 Oct 2026 16:10:42 +0200
Subject: [PATCH] reject e2e params with kem_ct and without kem_key (#1901)

---
 src/Simplex/Messaging/Crypto/Ratchet.hs    | 12 ++++++++----
 tests/AgentTests/ConnectionRequestTests.hs |  5 +++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/Simplex/Messaging/Crypto/Ratchet.hs b/src/Simplex/Messaging/Crypto/Ratchet.hs
index b38f2b5d1..fe74d772a 100644
--- a/src/Simplex/Messaging/Crypto/Ratchet.hs
+++ b/src/Simplex/Messaging/Crypto/Ratchet.hs
@@ -119,7 +119,7 @@ import Simplex.Messaging.Crypto.SNTRUP761.Bindings
 import Simplex.Messaging.Encoding
 import Simplex.Messaging.Encoding.String
 import Simplex.Messaging.Parsers (defaultJSON, parseE, parseE')
-import Simplex.Messaging.Util (($>>=), (<$?>))
+import Simplex.Messaging.Util ((<$?>))
 import Simplex.Messaging.Version
 import Simplex.Messaging.Version.Internal
 import UnliftIO.STM
@@ -327,9 +327,13 @@ instance StrEncoding AnyE2ERatchetParamsUri where
             Nothing -> pure $ AnyE2ERatchetParamsUri SRKSProposed a $ E2ERatchetParamsUri vr k1 k2 Nothing
       _ -> fail "bad e2e params"
     where
-      kemP query =
-        queryParam_ "kem_key" query
-          $>>= \k -> Just . kemParams k <$> queryParam_ "kem_ct" query
+      kemP query = do
+        k_ <- queryParam_ "kem_key" query
+        ct_ <- queryParam_ "kem_ct" query
+        case (k_, ct_) of
+          (Just k, _) -> pure $ Just $ kemParams k ct_
+          (Nothing, Nothing) -> pure Nothing
+          (Nothing, Just _) -> fail "bad e2e params: kem_ct without kem_key"
       kemParams k = \case
         Nothing -> ARKP SRKSProposed $ RKParamsProposed k
         Just ct -> ARKP SRKSAccepted $ RKParamsAccepted ct k
diff --git a/tests/AgentTests/ConnectionRequestTests.hs b/tests/AgentTests/ConnectionRequestTests.hs
index c3b255139..d76d8d305 100644
--- a/tests/AgentTests/ConnectionRequestTests.hs
+++ b/tests/AgentTests/ConnectionRequestTests.hs
@@ -20,6 +20,8 @@ module AgentTests.ConnectionRequestTests
 
 import AgentTests.EqInstances ()
 import Data.ByteString (ByteString)
+import qualified Data.ByteString.Char8 as B
+import Data.Either (isLeft)
 import Network.HTTP.Types (urlEncode)
 import Simplex.Messaging.Agent.Protocol
 import qualified Simplex.Messaging.Crypto as C
@@ -285,6 +287,9 @@ connectionRequestTests =
       contactAddressV6 #== ("https://simplex.chat/contact#/?v=1-2&smp=" <> url queueStr) -- adjusted to v6
       contactAddressV6 #== ("https://simplex.chat/contact#/?v=2-2&smp=" <> url queueStr)
       contactAddressClientData #==# ("simplex:/contact#/?v=6-8&smp=" <> url queueStr <> "&data=" <> url "{\"type\":\"group_link\", \"group_link_id\":\"abc\"}")
+    it "should reject KEM ciphertext without KEM key in e2e params" $
+      strDecode @(RcvE2ERatchetParamsUri 'C.X448) (strEncode testE2ERatchetParams <> "&kem_ct=" <> strEncode (B.replicate 1039 '\0'))
+        `shouldSatisfy` isLeft
     it "should serialize / parse queue address, connection invitations and contact addresses as binary" $ do
       smpEncodingTest queue
       smpEncodingTest queueNoQM -- this passes, no queue mode patch in SMPQueueUri encoding