using LL_Encrypt()

Tim Redfern

Other Parts Discussed in Thread: CC2541

Hi I'm trying to use LL_Encrypt() to encrypt the data payload of my BLE project without using an encrypted connection.

I can succesfully do this, but iI can't decrypt it at the other side and it is not clear what form of AES it is.

BLE spec says that BLE uses AES-CCM exclusively, but I'm confused because that would apparently require an IV code. Maybe this is defined elsewhere in the BT stack?

Does anyone have any information on LL_Encrypt() and how to decrypt its payload?

Thanks

Tim

over 10 years ago

0 Dhaval V over 10 years ago

Genius 4470 points

How are you trying to decrypt the received data? I mean which software you are using and what is the command?

0 Tim Redfern over 10 years ago in reply to Dhaval V

Expert 1360 points

Trying to decrypt using the CCCrypt library in iOS.

Looking at this more closely, I believe the LL_Encrypt() command has to be setup when the encrypted connection is established and then is used by the BT stack.

0 Tim Redfern over 10 years ago in reply to Tim Redfern

Expert 1360 points

SO, it turns out that on its own LL_Encrypt uses aes-128-ecb standard

The byte order is reversed when feeding to CCCrypt

I suppose its up to the user application to implement any kind of cipher-block chaining

0 Dhaval V over 10 years ago in reply to Tim Redfern

Genius 4470 points

Yes, you are correct. It is using aes-128-ecb for encryption.

0 arlon gamer over 10 years ago

Prodigy 25 points

Hi Tim,

I have the same issue where I can't decrypt on IOS a successfully encrypted payload on chip, in advertising mode.
Were you able to solve this ?
In general, does LL_Encrypt() command really need to be setup in a connection?

Thanks a lot,
Arlon

0 Tim Redfern over 10 years ago in reply to arlon gamer

Expert 1360 points

Hi, I was able to solve this.

I'm using LL_Encrypt to create my own encryption scheme rather than using the bluetooth stack to make an encrypted connection. I used CCCrypt on the iOS side to decrypt the data. LL_encrypt on its own does ECB encryption, I implemented CBC (cipher block chaining) on both the cc2541 and the iOS side as I couldn't get it to work any other way.

Tim

Bluetooth®︎

Bluetooth forum

using LL_Encrypt()