document that error checking still needs to be performed

draft-kwiatkowski-tls-ecdhe-mlkem.md

@@ -153,6 +153,18 @@ For all groups, the server MUST perform the encapsulation key check
 described in Section 7.2 of {{FIPS203}} on the client's encapsulation
 key, and abort with an illegal_parameter alert if it fails.
 
+For all groups, the client MUST perform the ciphertext check described
+in Section 7.3 of {{FIPS203}} on the server's encapsulated key,
+and abort with an illegal_parameter alert if it fails.
+
+For all groups, both client and server MUST perform the key share checks
+for the classical part, as described in Section 4.2.8.2 of {{!RFC8446}},
+and abort with an illegal_parameter alert if it fails.
+
+For all groups, both client and server MUST check if the peer's key share
+size matches the negotiated groups and abort with an illegal_parameter alert
+if it fails.
+
 ### Shared secret
 
 For X25519MLKEM768, the shared secret is the concatenation of the ML-KEM
@@ -172,6 +184,10 @@ defined in Section 7.4.2 of {{!RFC8446}}.
 The size of the shared secret is 80 bytes (48 bytes for the ECDH part and
 32 bytes for the ML-KEM part).
 
+For all groups, both client and server MUST perform the shared secret
+check described in Section 7.4.2 of {{!RFC8446}} and abort the
+connection with an illegal_parameter if it fails.
+
 # Security Considerations
 
 The same security considerations as those described in {{hybrid}} apply to the approach used by this document.