uhttpd: add support to generate EC keys

This adds the key_type and ec_curve options to enable the generation of
EC keys during initialization, using openssl or the new options added to
px5g.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
(cherry picked from commit 7f2b230b3b9d0a7fb758db3a9b1958845506a5a3)

package/network/services/uhttpd/Makefile

@@ -8,7 +8,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=uhttpd
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=$(PROJECT_GIT)/project/uhttpd.git

package/network/services/uhttpd/files/uhttpd.config

@@ -118,9 +118,17 @@ config cert defaults
 	# Validity time
 	option days		730
 
+	# key type: rsa or ec
+	option key_type		rsa
+
 	# RSA key size
 	option bits		2048
 
+	# EC curve name
+	# Curve names vary between mbedtls/px5g and openssl
+	# P-256 or P-384 are guaranteed to work
+	option ec_curve		P-256
+
 	# Location
 	option country		ZZ
 	option state		Somewhere

package/network/services/uhttpd/files/uhttpd.init

@@ -43,15 +43,19 @@ generate_keys() {
 	config_get state      "$cfg" state
 	config_get location   "$cfg" location
 	config_get commonname "$cfg" commonname
+	config_get key_type   "$cfg" key_type
+	config_get ec_curve   "$cfg" ec_curve
 
 	# Prefer px5g for certificate generation (existence evaluated last)
 	local GENKEY_CMD=""
+	local KEY_OPTS="rsa:${bits:-2048}"
 	local UNIQUEID=$(dd if=/dev/urandom bs=1 count=4 | hexdump -e '1/1 "%02x"')
+	[ "$key_type" = "ec" ] && KEY_OPTS="ec -pkeyopt ec_paramgen_curve:${ec_curve:-P-256}"
 	[ -x "$OPENSSL_BIN" ] && GENKEY_CMD="$OPENSSL_BIN req -x509 -sha256 -outform der -nodes"
 	[ -x "$PX5G_BIN" ] && GENKEY_CMD="$PX5G_BIN selfsigned -der"
 	[ -n "$GENKEY_CMD" ] && {
 		$GENKEY_CMD \
-			-days ${days:-730} -newkey rsa:${bits:-2048} -keyout "${UHTTPD_KEY}.new" -out "${UHTTPD_CERT}.new" \
+			-days ${days:-730} -newkey ${KEY_OPTS} -keyout "${UHTTPD_KEY}.new" -out "${UHTTPD_CERT}.new" \
 			-subj /C="${country:-ZZ}"/ST="${state:-Somewhere}"/L="${location:-Unknown}"/O="${commonname:-OpenWrt}$UNIQUEID"/CN="${commonname:-OpenWrt}"
 		sync
 		mv "${UHTTPD_KEY}.new" "${UHTTPD_KEY}"