hsmd: Create derive_secret and makesecret RPC for deriving pseudorand…

…om keys from HSM

hsmd/hsmd.c

@@ -660,6 +660,7 @@ static struct io_plan *handle_client(struct io_conn *conn, struct client *c)
 	case WIRE_HSMD_ECDH_REQ:
 	case WIRE_HSMD_CHECK_FUTURE_SECRET:
 	case WIRE_HSMD_GET_OUTPUT_SCRIPTPUBKEY:
+	case WIRE_HSMD_DERIVE_SECRET:
 	case WIRE_HSMD_CANNOUNCEMENT_SIG_REQ:
 	case WIRE_HSMD_NODE_ANNOUNCEMENT_SIG_REQ:
 	case WIRE_HSMD_CUPDATE_SIG_REQ:
@@ -681,6 +682,7 @@ static struct io_plan *handle_client(struct io_conn *conn, struct client *c)
 	case WIRE_HSMD_SIGN_WITHDRAWAL_REPLY:
 	case WIRE_HSMD_SIGN_INVOICE_REPLY:
 	case WIRE_HSMD_INIT_REPLY:
+	case WIRE_HSMD_DERIVE_SECRET_REPLY:
 	case WIRE_HSMSTATUS_CLIENT_BAD_REQUEST:
 	case WIRE_HSMD_SIGN_COMMITMENT_TX_REPLY:
 	case WIRE_HSMD_VALIDATE_COMMITMENT_TX_REPLY:

hsmd/hsmd_wire.csv

@@ -281,3 +281,11 @@ msgdata,hsmd_sign_option_will_fund_offer,channel_fee_proportional_basis_max,u16,
 
 msgtype,hsmd_sign_option_will_fund_offer_reply,126
 msgdata,hsmd_sign_option_will_fund_offer_reply,rsig,secp256k1_ecdsa_signature,
+
+# Reply with the derived secret
+msgtype,hsmd_derive_secret_reply,27
+msgdata,hsmd_derive_secret_reply,secret,secret,
+
+msgtype,hsmd_derive_secret,127
+msgdata,hsmd_derive_secret,len,u16,
+msgdata,hsmd_derive_secret,info,u8,len

hsmd/libhsmd.c

@@ -23,11 +23,13 @@ struct secret *dev_force_bip32_seed;
 #endif
 
 /*~ Nobody will ever find it here!  hsm_secret is our root secret, the bip32
- * tree and bolt12 payer_id keys are derived from that, and cached here. */
+ * tree, bolt12 payer_id keys and derived_secret are derived from that, and
+ * cached here. */
 struct {
 	struct secret hsm_secret;
 	struct ext_key bip32;
 	secp256k1_keypair bolt12;
+	struct secret derived_secret;
 } secretstuff;
 
 /* Have we initialized the secretstuff? */
@@ -117,6 +119,7 @@ bool hsmd_check_client_capabilities(struct hsmd_client *client,
 	case WIRE_HSMD_SIGN_MESSAGE:
 	case WIRE_HSMD_GET_OUTPUT_SCRIPTPUBKEY:
 	case WIRE_HSMD_SIGN_BOLT12:
+	case WIRE_HSMD_DERIVE_SECRET:
 		return (client->capabilities & HSM_CAP_MASTER) != 0;
 
 	/*~ These are messages sent by the HSM so we should never receive them. */
@@ -145,6 +148,7 @@ bool hsmd_check_client_capabilities(struct hsmd_client *client,
 	case WIRE_HSMD_SIGN_MESSAGE_REPLY:
 	case WIRE_HSMD_GET_OUTPUT_SCRIPTPUBKEY_REPLY:
 	case WIRE_HSMD_SIGN_BOLT12_REPLY:
+	case WIRE_HSMD_DERIVE_SECRET_REPLY:
 		break;
 	}
 	return false;
@@ -257,6 +261,22 @@ static void hsm_channel_secret_base(struct secret *channel_seed_base)
 		    "peer seed", strlen("peer seed"));
 }
 
+/* This will derive pseudorandom secret Key from a derived key */
+static u8 *handle_derive_secret(struct hsmd_client *c, const u8 *msg_in)
+{
+	u8 *info;
+	struct secret secret;
+
+	if (!fromwire_hsmd_derive_secret(tmpctx, msg_in, &info))
+		return hsmd_status_malformed_request(c, msg_in);
+
+	hkdf_sha256(&secret, sizeof(struct secret), NULL, 0,
+		    &secretstuff.derived_secret, sizeof(&secretstuff.derived_secret),
+		    info, tal_bytelen(info));
+
+	return towire_hsmd_derive_secret_reply(NULL, &secret);
+}
+
 /*~ This gets the seed for this particular channel. */
 static void get_channel_seed(const struct node_id *peer_id, u64 dbid,
 			     struct secret *channel_seed)
@@ -1593,9 +1613,12 @@ u8 *hsmd_handle_client_message(const tal_t *ctx, struct hsmd_client *client,
 		return handle_sign_remote_htlc_to_us(client, msg);
 	case WIRE_HSMD_SIGN_DELAYED_PAYMENT_TO_US:
 		return handle_sign_delayed_payment_to_us(client, msg);
+	case WIRE_HSMD_DERIVE_SECRET:
+		return handle_derive_secret(client, msg);
 
 	case WIRE_HSMD_DEV_MEMLEAK:
 	case WIRE_HSMD_ECDH_RESP:
+	case WIRE_HSMD_DERIVE_SECRET_REPLY:
 	case WIRE_HSMD_CANNOUNCEMENT_SIG_REPLY:
 	case WIRE_HSMD_CUPDATE_SIG_REPLY:
 	case WIRE_HSMD_CLIENT_HSMFD_REPLY:
@@ -1760,6 +1783,12 @@ u8 *hsmd_init(struct secret hsm_secret,
 		    sizeof(secretstuff.hsm_secret),
 		    "onion reply secret", strlen("onion reply secret"));
 
+	/* We derive the derived_secret key for generating pseudorandom keys
+	 * by taking input string from the makesecret RPC */
+	hkdf_sha256(&secretstuff.derived_secret, sizeof(struct secret), NULL, 0,
+		    &secretstuff.hsm_secret, sizeof(secretstuff.hsm_secret),
+		    "derived secrets", strlen("derived secrets"));
+
 	/*~ Note: marshalling a bip32 tree only marshals the public side,
 	 * not the secrets!  So we're not actually handing them out here!
 	 */

lightningd/hsm_control.c

@@ -4,7 +4,9 @@
 #include <common/ecdh.h>
 #include <common/errcode.h>
 #include <common/hsm_encryption.h>
+#include <common/json_command.h>
 #include <common/json_helpers.h>
+#include <common/json_tok.h>
 #include <common/param.h>
 #include <common/type_to_string.h>
 #include <errno.h>
@@ -146,6 +148,45 @@ static struct command_result *json_getsharedsecret(struct command *cmd,
 	return command_success(cmd, response);
 }
 
+static struct command_result *json_makesecret(struct command *cmd,
+					   const char *buffer,
+					   const jsmntok_t *obj UNNEEDED,
+					   const jsmntok_t *params)
+{
+	u8 *info;
+	struct json_stream *response;
+	struct secret secret;
+
+	if (!param(cmd, buffer, params,
+		   p_req("info_hex", param_bin_from_hex, &info),
+		   NULL))
+		return command_param_failed();
+
+	u8 *msg = towire_hsmd_derive_secret(cmd, info);
+	if (!wire_sync_write(cmd->ld->hsm_fd, take(msg)))
+		return command_fail(cmd, LIGHTNINGD,
+                     "Could not write to HSM: %s", strerror(errno));
+
+
+	msg = wire_sync_read(tmpctx, cmd->ld->hsm_fd);
+	if (!fromwire_hsmd_derive_secret_reply(msg, &secret))
+		return command_fail(cmd, LIGHTNINGD,
+                     "Bad reply from HSM: %s", strerror(errno));
+
+
+	response = json_stream_success(cmd);
+	json_add_secret(response, "secret", &secret);
+	return command_success(cmd, response);
+}
+
+static const struct json_command makesecret_command = {
+	"makesecret",
+	"utility",
+	&json_makesecret,
+	"Get a pseudorandom secret key, using an info string."
+};
+AUTODATA(json_command, &makesecret_command);
+
 static const struct json_command getsharedsecret_command = {
 	"getsharedsecret",
 	"utility", /* FIXME: Or "crypto"?  */