The Amazon link to the Kpw-Gen2 sources is working today.
The released source bundle for 5.4.0 does not contain the signing keys required to install packages with the Kindle's installer.
Not any different than before (they have never released the private key of the key-pair).
But this time they goofed up - -
The gnutls_2.8.4 used in the build is GPLv3 !!
With GPLv3 license, the vendor **must** release any keys required to load end-user created software to the device.
ALL RIGHT WORLD, stop complaining and just call in the first-string legal team.
Amazon just shot themselves in the foot, and we can help them bleed.