lightningd: add signmessage JSON command.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - JSON API: `listfunds` now lists a blockheight for confirmed transactions, and has `connected` and `state` fields for channels, like `listpeers`.
 - JSON API: `fundchannel_start` now includes field `scriptpubkey`
 - JSON API: New method `listtransactions`
+- JSON API: `signmessage` will now create a signature from your node on a message.
 - Plugin: new notifications `sendpay_success` and `sendpay_failure`.
 - Protocol: nodes now announce features in `node_announcement` broadcasts.
 - Protocol: we now offer `option_gossip_queries_ex` for finegrained gossip control.

lightningd/Makefile

@@ -96,7 +96,10 @@ LIGHTNINGD_SRC :=				\
 	lightningd/subd.c			\
 	lightningd/watch.c
 
-LIGHTNINGD_OBJS := $(LIGHTNINGD_SRC:.c=.o)
+LIGHTNINGD_SRC_NOHDR :=				\
+	lightningd/signmessage.c
+
+LIGHTNINGD_OBJS := $(LIGHTNINGD_SRC:.c=.o) $(LIGHTNINGD_SRC_NOHDR:.c=.o)
 
 # Make sure these depend on everything.
 ALL_OBJS += $(LIGHTNINGD_OBJS)
@@ -124,9 +127,9 @@ lightningd/gen_channel_state_names.h: lightningd/channel_state.h ccan/ccan/cdump
 
 check-source: $(LIGHTNINGD_SRC:%=check-src-include-order/%) $(LIGHTNINGD_SRC_NOHDR:%=check-src-include-order/%)
 check-source: $(LIGHTNINGD_HEADERS_NOGEN:%=check-hdr-include-order/%)
-check-source-bolt: $(LIGHTNINGD_SRC:%=bolt-check/%) $(LIGHTNINGD_HEADERS_NOGEN:%=bolt-check/%)
+check-source-bolt: $(LIGHTNINGD_SRC:%=bolt-check/%) $(LIGHTNINGD_SRC_NOHDR:%=bolt-check/%) $(LIGHTNINGD_HEADERS_NOGEN:%=bolt-check/%)
 
-check-whitespace: $(LIGHTNINGD_SRC:%=check-whitespace/%) $(LIGHTNINGD_HEADERS_NOGEN:%=check-whitespace/%)
+check-whitespace: $(LIGHTNINGD_SRC:%=check-whitespace/%) $(LIGHTNINGD_SRC_NOHDR:%=check-whitespace/%) $(LIGHTNINGD_HEADERS_NOGEN:%=check-whitespace/%)
 
 check-makefile: check-lightningd-makefile
 check-lightningd-makefile:

lightningd/signmessage.c

@@ -0,0 +1,60 @@
+#include <common/json_helpers.h>
+#include <common/jsonrpc_errors.h>
+#include <common/param.h>
+#include <common/type_to_string.h>
+#include <common/utils.h>
+#include <errno.h>
+#include <gossipd/gen_gossip_wire.h>
+#include <hsmd/gen_hsm_wire.h>
+#include <string.h>
+#include <wire/wire_sync.h>
+
+static struct command_result *json_signmessage(struct command *cmd,
+					       const char *buffer,
+					       const jsmntok_t *obj UNNEEDED,
+					       const jsmntok_t *params)
+{
+	const char *message;
+	secp256k1_ecdsa_recoverable_signature rsig;
+	struct json_stream *response;
+	u8 sig[64], recidu8, *msg;
+	int recid;
+
+	if (!param(cmd, buffer, params,
+		   p_req("message", param_string, &message),
+		   NULL))
+		return command_param_failed();
+
+	if (strlen(message) > 65535)
+		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+				    "Message must be < 64k");
+
+	msg = towire_hsm_sign_message(NULL,
+				      tal_dup_arr(tmpctx, u8, (u8 *)message,
+						  strlen(message), 0));
+	if (!wire_sync_write(cmd->ld->hsm_fd, take(msg)))
+		fatal("Could not write to HSM: %s", strerror(errno));
+
+	msg = wire_sync_read(tmpctx, cmd->ld->hsm_fd);
+	if (!fromwire_hsm_sign_message_reply(msg, &rsig))
+		fatal("HSM gave bad hsm_sign_message_reply %s",
+		      tal_hex(msg, msg));
+
+	secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_ctx,
+								sig, &recid,
+								&rsig);
+	response = json_stream_success(cmd);
+	json_add_hex(response, "signature", sig, sizeof(sig));
+	recidu8 = recid;
+	json_add_hex(response, "recid", &recidu8, sizeof(recidu8));
+	return command_success(cmd, response);
+}
+
+static const struct json_command json_signmessage_cmd = {
+	"signmessage",
+	"utility",
+	json_signmessage,
+	"Create a digital signature of {message}",
+};
+AUTODATA(json_command, &json_signmessage_cmd);
+