AUDIO-AM62D-EVM: AM62d linux encrypted/decrepted and tiboot3.bin signing etc. security questions

Part Number: AUDIO-AM62D-EVM

Tool/software:

how to enable encrypt/decrypt support for linux boot.bin and kernel linux.bin/recovery kernel? in sdk yocto build, I can see the scripts ti-k3-secdev/scripts/secure-binary-image.sh is used to sign each binary, but cannot find out where tiboot3.bin is signed. Also I see one presentation showing

## Loading kernel from FIT Image at 90000000 ...
Using 'k3 am62x lp sk.dtb' configuration
Authentication passed -- Kernel authentication
## Loading fdt from FIT Image at 90000000 ...
Using 'k3 am62x lp sk.dtb' configuration
Trying 'k3am62x lp sk.dtb' fdt subimage
Authentication passed -- Kernel DTB authentication
Booting using the fdt blob at 0x9076bc3c

but on AM62d-evm, kernel and kernel DTB does not sign. 

Questions for TI security experts: For AM62D yocto build

1) where is tiboot3.bin is signed? and the script is used to sign?

2) where and how the kernel and kernel DTB are signed (and/or encrypted)? can you provide the example scripts to do that?

3) I see the code supporting signing but not encrypt/decrypt, but also seeing some documents mentioned encrypt/decrypt. could you point out where is the code (if available) and formal documents/links supporting encrypt/decrypt of boot images (tiboot3, tispl, u-boot etc) and kernel image (linux.bin/recovry kernel)? more specific and better.

Thanks Aiping