diff --git a/include/ircd/m/device.h b/include/ircd/m/device.h
index c48ff5014..9843909f0 100644
--- a/include/ircd/m/device.h
+++ b/include/ircd/m/device.h
@@ -16,8 +16,34 @@ namespace ircd::m
 	struct device;
 	struct device_keys;
 	struct device_list_update;
+	struct cross_signing_key;
 }
 
+struct ircd::m::cross_signing_key
+:json::tuple
+<
+	/// Required. The ID of the user the key belongs to.
+	json::property<name::user_id, json::string>,
+
+	/// Required. What the key is used for.
+	/// One of: ["master", "self_signing", "user_signing"]
+	json::property<name::usage, json::string>,
+
+	/// Required. The public key. The object must have exactly one property,
+	/// whose name is in the form <algorithm>:<unpadded_base64_public_key>,
+	/// and whose value is the unpadded base64 public key.
+	json::property<name::keys, json::object>,
+
+	/// Signatures of the key, calculated using the process described at
+	/// Signing JSON. Optional for the master key. Other keys must be signed
+	/// by the user's master key.
+	json::property<name::signatures, json::object>
+>
+{
+	using super_type::tuple;
+	using super_type::operator=;
+};
+
 struct ircd::m::device_keys
 :json::tuple
 <
diff --git a/include/ircd/m/name.h b/include/ircd/m/name.h
index 7fb7b9144..81a6fb055 100644
--- a/include/ircd/m/name.h
+++ b/include/ircd/m/name.h
@@ -209,4 +209,6 @@ struct ircd::m::name
 	static constexpr const char *const msgtype {"msgtype"};
 	static constexpr const char *const format {"format"};
 	static constexpr const char *const formatted_body {"formatted_body"};
+
+	static constexpr const char *const usage {"usage"};
 };
diff --git a/matrix/name.cc b/matrix/name.cc
index d6d5c3e93..67116c5a8 100644
--- a/matrix/name.cc
+++ b/matrix/name.cc
@@ -188,3 +188,5 @@ constexpr const char *const ircd::m::name::body;
 constexpr const char *const ircd::m::name::msgtype;
 constexpr const char *const ircd::m::name::format;
 constexpr const char *const ircd::m::name::formatted_body;
+
+constexpr const char *const ircd::m::name::usage;