SWRA803 February   2020 CC2540 , CC2541

 

  1.   1
  2. 1Summary
  3. 2Vulnerability
  4. 3Revision History

1 Summary

In the CC254x OAD solution:

  • aesCrypt function in EBL/app/sbl_exec.c is used to encrypt the OAD image (64 bytes of data at a time)
  • imgCrypt function in BEM/app/bem_main.c is used to decrypt the OAD image

AES-CTR cryptographic function is used in both the encryption functions above. The cryptographic function implementation resets the AES-CTR counter to its initial value every 4 AES blocks (64-bytes), resulting in keystream repetition every 64-bytes. This vulnerability can potentially be used to decrypt a firmware image without having to recover the AES key.