SBSFU SECoreBin failing to build with different AES Key

[kerp0w]

I'm trying to build the SECoreBIn, and have changed the key (OEM_COMPANY_1) in:

STM32CubeExpansion_SBSFU_V2.3.0/Projects/NUCLEO-G071RB/Applications/2_Images/2_Images_SECoreBin/Binary/OEM_KEY_COMPANY1_key_AES_CBC.bin

If I have understood correctly from the Getting strated guilde, this is the symetric AES key used to encrypt the binary in the postscript.sh later.

However, when I try to buld the SECoreBin, I am getting the following error from the python prepareimage.py script:

21:38:49 **** Incremental Build of configuration Debug for project NUCLEO-G071RB_2_Images_SECoreBin ****
make all 
"../../prebuild2.sh" "../.."
../..
Python 3.7.5
prepareimage with python script
python /Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/prepareimage.py conf ../../../Inc/se_crypto_config.h
SECBOOT_ECCDSA_WITH_AES128_CBC_SHA256 selected
ECCDSA_WITH_AES128_CBC_SHA256
python /Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/prepareimage.py trans -a GNU -k ../../../Binary/OEM_KEY_COMPANY1_key_AES_CBC.bin -f SE_ReadKey -s .SE_Key_Data -v V6M
Traceback (most recent call last):
 File "/Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/prepareimage.py", line 759, in <module>
 args()
 File "/Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/prepareimage.py", line 756, in args
 subcmds[args.subcmd](args)
 File "/Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/prepareimage.py", line 53, in do_trans
 key = keys.load(args.key)
 File "/Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/keys.py", line 274, in load
 key = SigningKey.from_pem(pem)
 File "/Users/Development/AgileProject/G0_SBSFU/py3_env/lib/python3.7/site-packages/ecdsa/keys.py", line 828, in from_pem
 privkey_pem = string[string.index(b("-----BEGIN EC PRIVATE KEY-----")):]
ValueError: subsection not found
python /Users/Development/AgileProject/G0_SBSFU/STM32CubeExpansion_SBSFU_V2.3.0/Middlewares/ST/STM32_Secure_Engine/Utilities/KeysAndImages/prepareimage.py trans -a GNU -k ../../../Binary/OEM_KEY_COMPANY1_key_AES_CBC.bin -f SE_ReadKey -s .SE_Key_Data -v V6M : failed
make[1]: *** [makefile:74: pre-build] Error 1
make: *** [makefile:42: all] Error 2
"make all" terminated with exit code 2. Build might be incomplete.
 
21:38:51 Build Failed. 2 errors, 0 warnings. (took 1s.899ms)
 

[alister]

>ValueError: subsection not found

The string.index's raising ValueError because it can't find "-----BEGIN EC PRIVATE KEY-----".

https://docs.python.org/3/library/stdtypes.html