crackle cracks BLE Encryption (AKA Bluetooth Smart).

crackle exploits a flaw in the BLE pairing process that allows an attacker to guess or very quickly brute force the TK (Temporary Key). With the TK and other data collected from the pairing process, the STK (Short Term Key) and later the LTK (Long Term Key) can be collected.

With the STK and LTK, all communications between the master and the slave can be decrypted.

Before attempting to use crackle, review the FAQ to determine whether it is the appropriate tool to use in your situation.

crackle was written by Mike Ryan mikeryan@lacklustre.net See web site for more info: http://lacklustre.net/projects/crackle/

Table of Contents

• Modes of Operation
  • Crack TK
  • Decrypt with LTK
• Running crackle
• Sample Files
• Frequently Asked Questions
• See Also
• Thanks

Modes of Operation

crackle has two major modes of operation: Crack TK and Decrypt with LTK.

Crack TK

This is the default mode used when providing crackle with an input file using -i.

In Crack TK mode, crackle brute forces the TK used during a BLE pairing event. crackle exploits the fact that the TK in Just Works(tm) and 6-digit PIN is a value in the range [0,999999] padded to 128 bits.

crackle employs several methods to perform this brute force: a very fast method if all pairing packets are present in the input file, and a slow method if a minimum set of packets is present.

To use this mode, launch crackle with an input PCAP or PcapNG file containing one or more connections with a BLE pairing conversation. crackle will analyze all connections, determine whether it is possible to crack a given connection, and automatically choose the best strategy to crack each one.

If the TK successfully cracks, crackle will derive the remaining keys used to encrypt the rest of the connection and will decrypt any encrypted packets that follow. If the LTK is exchanged (typically the first thing done after encryption is established) crackle will output this value to stdout. The LTK can be used to decrypt any future communications between the two endpoints.

Provide crackle with an output file using -o to create a new PCAP file containing the decrypted data (in addition to the already unencrypted data).

Example usage:

$ crackle -i input.pcap -o decrypted.pcap

Decrypt with LTK

In Decrypt with LTK mode, crackle uses a user-supplied LTK to decrypt communications between a master and slave. This mode is identical to the decryption portion of Crack TK mode.

Example usage:

$ crackle -i encrypted.pcap -o decrypted.pcap -l 81b06facd90fe7a6e9bbd9cee59736a7

Running Crackle

Crack TK Mode

In Crack TK mode, crackle requires a PCAP file that contains a BLE pairing event. The best way to generate such a file is to use an Ubertooth to capture a pairing event between a master and a slave.

To check if your PCAP file contains all the necessary packets, run crackle with the -i option:

crackle -i <file.pcap>

crackle will analyze each connection in the input file and output the results of its analysis to stdout. If you have all the components of a pairing conversation, the output will look like this:

Analyzing connection 0:
  xx:xx:xx:xx:xx:xx (public) -> yy:yy:yy:yy:yy:yy (public)
  Found 13 encrypted packets

  Cracking with strategy 0, 20 bits of entropy

  !!!
  TK found: 412741
  !!!

  Decrypted 12 packets
  LTK found: 81b06facd90fe7a6e9bbd9cee59736a7

Specify an output file with -o to decrypt packets!

To decrypt all packets, add the -o option:

crackle -i <file.pcap> -o <output.pcap>

The output file will contain decrypted versions of all the encrypted packets from the original PCAP, as well as all the unencrypted packets. Note that CRCs are not recalculated, so the CRCs of decrypted packets will be incorrect.

Decrypt with LTK

In Decrypt with LTK mode, crackle requires a PCAP file that contains at a minimum LL_ENC_REQ and LL_ENC_RSP packets and the LTK used to encrypt the communications.

The format for LTK is a 128 bit hexadecimal number with no spaces or separators, most-significant octet to least-significant octet. Example:

-l 81b06facd90fe7a6e9bbd9cee59736a7

To check if your PCAP file contains all the necessary packets, run crackle with -i and -l:

crackle -i <file.pcap> -l <ltk>

If you have both of the required packets, the program should produce output similar to this:

Analyzing connection 0:
  xx:xx:xx:xx:xx:xx (public) -> yy:yy:yy:yy:yy:yy (public)
  Found 9 encrypted packets
  Decrypted 6 packets

Specify an output file with -o to decrypt packets!

To decrypt all packets, add the -o option:

crackle -i <file.pcap> -o <out.pcap> -l <ltk>

The output file will be produced similarly to the output file described above.

Sample Files

The test files included in the tests directory serve as interesting input for playing with crackle. Review the README files included in each test's subdirectory.

Grab some sample files for cracking with crackle. Refer to the README inside the tarball for more information:

https://lacklustre.net/bluetooth/crackle-sample.tgz

Frequently Asked Questions

We have compiled a list of Frequently Asked Questions.

See Also

• Ubertooth: http://ubertooth.sourceforge.net/
• libbtbb: http://libbtbb.sourceforge.net/
• #ubertooth on irc.freenode.net

Thanks

Major thanks go to Mike Ossmann and Dominic Spill from the Ubertooth project. None of this would be possible without them.

Big time thanks go to Mike Kershaw/dragorn of Kismet for help creating and working with PCAP files.

Thanks go to the rest of #ubertooth on irc.freenode.net.