Gate v2 logins on upstream's v2 encryption check

src/api/identity.rs

@@ -518,13 +518,13 @@ async fn password_login(
     authenticated_response(&user, &mut device, auth_tokens, twofactor_token, conn, ip).await
 }
 
-/// Like upstream's `ClientVersionValidator`, a V2 account logs in only from a client that sends its version and is at
+/// Like upstream's `ClientVersionValidator`, a V2 account ([`User::has_v2_encryption`]) logs in only from a client that
-/// least 2025.11.0 (upstream also refuses a missing header for V1 accounts). Called right after the credentials are
+/// sends its version and is at least 2025.11.0 (upstream also refuses a missing header for V1 accounts). Called right
-/// checked, like upstream, so that it doesn't tell anyone else which accounts are V2.
+/// after the credentials are checked, like upstream, so that it doesn't tell anyone else which accounts are V2.
 ///
-/// Ref: <https://github.com/bitwarden/server/blob/2028f0a5cc9d8ab8ff8475029085f29f81483598/src/Identity/IdentityServer/RequestValidators/ClientVersionValidator.cs#L42-L69>
+/// Ref: <https://github.com/bitwarden/server/blob/8da186ad73f80d37157fe6fd42323e4284e83ec1/src/Identity/IdentityServer/RequestValidators/ClientVersionValidator.cs#L31-L72>
 fn check_client_version(user: &User, client_version: Option<&semver::Version>, ip: &ClientIp) -> EmptyResult {
-    let Some((error, description)) = client_version_error(user.is_v2(), client_version) else {
+    let Some((error, description)) = client_version_error(user.has_v2_encryption(), client_version) else {
         return Ok(());
     };
     Err(crate::error::Error::from((

src/db/models/user.rs

@@ -194,6 +194,19 @@ impl User {
         self.signed_public_key.is_some() && self.security_state.is_some() && self.security_version.is_some()
     }
 
+    /// Upstream's `HasV2Encryption`: a private key wrapped as `CoseEncrypt0B64` (type 7) and security version 2.
+    /// Upstream only uses it to decide which accounts need a v2-capable client.
+    ///
+    /// Ref: <https://github.com/bitwarden/server/blob/8da186ad73f80d37157fe6fd42323e4284e83ec1/src/Core/Entities/User.cs#L245-L278>
+    pub fn has_v2_encryption(&self) -> bool {
+        self.security_version == Some(2)
+            && self
+                .private_key
+                .as_deref()
+                .and_then(|private_key| private_key.split_once('.'))
+                .is_some_and(|(enc_type, _)| enc_type.parse::<u8>() == Ok(7))
+    }
+
     pub fn check_valid_password(&self, password: &str) -> bool {
         crypto::verify_password_hash(
             password.as_bytes(),
@@ -751,4 +764,21 @@ mod tests {
         // An absent key id stays optional
         assert_eq!(serde_json::from_str::<Option<KeyId>>("null").unwrap(), None);
     }
+
+    #[test]
+    fn test_has_v2_encryption() {
+        let user = |private_key: Option<&str>, security_version: Option<i32>| {
+            let mut user = User::new("user@example.com", None);
+            user.private_key = private_key.map(String::from);
+            user.security_version = security_version;
+            user
+        };
+
+        assert!(user(Some("7.cose"), Some(2)).has_v2_encryption());
+        assert!(!user(Some("7.cose"), Some(1)).has_v2_encryption());
+        assert!(!user(Some("7.cose"), None).has_v2_encryption());
+        assert!(!user(Some("2.iv|data|mac"), Some(2)).has_v2_encryption());
+        assert!(!user(Some("7"), Some(2)).has_v2_encryption());
+        assert!(!user(None, Some(2)).has_v2_encryption());
+    }
 }