K5 Having trouble with package signing for custom Kindlet on K5 Touch

Hi, I'm new to Kindle hacking and have been trying to get a Hello World kindlet running on my K5 touch for the last while. Here's some info about my Kindle:

Device: Kindle Touch WiFi
Firmware Version: Kindle 5.1.2 (1679530004)
JBPatch: 4.0.0

I've been roughly following this and this (outdated) and combining that with info from my friend and other things I've come across on this site. I copied Kindlet-2.1.jar off my Kindle, which slightly differs from the first tutorial I linked and significantly differs from the second. I copied the com directory from the root of the jar into my project folder.

Here's my code and directory setup:
developer.keystore: downloaded from here, the latest one (2012-11-06)
kindlet/Main.java:

test.manifest:

build.sh:


In order to build my app, I run my build.sh script, which produces app.azw2. Then, I put it on my Kindle via usb in the documents directory. However, when I try to open the kindlet, I get "This item is not signed by an authorized developer. Please contact the developer." I don't get this error when opening either JBPatch or KUAL, both of which installed fine.


Here's the output of showlog -f while opening the application (after ;debugOn):


Inside that monster of an error log I saw something about an exception being thrown inside untrusted code, so my app code might be wrong (it was kind of patched together and I don't know if I can use swing or what) but there's also a signing issue I think because it's saying the code is untrusted.

Things I've tried:
- Screaming into the void
- Building the JAR using Eclipse (was doing this initially until I made the build script)
- Signing my own developer keys per the second guide I linked above. This was strange because I made new keys and replaced the developer.keystore file on my Kindle at the right location, restarted, and was still unable to launch my app but also was able to launch JBPatch and KUAL. I am not really sure why that is the case but I'm pretty sure I installed it right; I mounted the root directory rw, copied the developer.keystore from my computer into the right location (/var/local/java/keystore/developer.keystore)
- Commenting out the javax.swing import line and the code that draws the textarea + reducing error reporting level. This showlog -f is much more manageable and has some useful information I think:

It looks like this is the crux of the problem:
java.security.NoSuchAlgorithmException: 1.2.840.113549.1.1.11 Signature not available
I don't really know what it wants me to do, though.

It might also be worth noting that I'm running javac 1.8.0_172 (I think the OpenJDK version).

Any advice or pointers in the right direction would be much appreciated! Thanks so much!