Dropbear: on lantiq target no longer supports ed25519 keys

[achelon5]

Maintainer: @<[email protected]>
Environment:
Model: Netgear DM200
Architecture: xRX200 rev 1.2
Target Platform: lantiq/xrx200_legacy
Firmware Version: OpenWrt 24.10.0-rc5 r28304-6dacba30a7 / LuCI openwrt-24.10 branch 25.006.62535~c9cc773

Description:

Dropbear is missing support for ed25519 keys in OpenWrt 24.10.0-rc5 on the DM200 build. Attempting SSH authentication with an ed25519 key results in "Permission denied" in the SSH client. Attempts to generate an ed25519 result in "Unknown key type 'ed25519'" when following the steps in the documentation https://openwrt.org/docs/guide-user/security/dropbear.public-key.auth.

root@dm200:~# dropbearkey -t ed25519 -f ~/.ssh/id_dropbear
Unknown key type 'ed25519'
Usage: dropbearkey -t <type> -f <filename> [-s bits]
-t type	Type of key to generate. One of:
		rsa
-f filename    Use filename for the secret key.
               ~/.ssh/id_dropbear is recommended for client keys.
-s bits	Key size in bits, should be a multiple of 8 (optional)
-y		Just print the publickey and fingerprint for the
		private key in <filename>.
-C		Specify the key comment (email).

This was a custom build using the firmware builder using the following packages:

base-files busybox ca-bundle dnsmasq dropbear firewall4 fstools kmod-gpio-button-hotplug kmod-leds-gpio kmod-ltq-atm-vr9 kmod-ltq-deu-vr9 kmod-ltq-ptm-vr9 kmod-ltq-vdsl-vr9 kmod-ltq-vdsl-vr9-mei kmod-nft-offload libc libgcc libustream-mbedtls logd ltq-vdsl-vr9-app mtd netifd nftables odhcp6c odhcpd-ipv6only procd procd-seccomp procd-ujail uci urandom-seed urngd luci lm-sensors snmpd