proxmark3/tools/hitag2crack

HiTag2 Cracking Suite

Author: Kevin Sheldrake kev@headhacking.com

Introduction

These tools are implementations of the four attacks detailed in the papers, Gone In 360 Seconds - Hijacking With HiTag 2 by Roel Verdult, Flavio Garcia and Josep Balasch, and Lock It And Still Lose It - on the (In)Security of Automotive Remote Keyless Entry Systems by Flavio Garcia, David Oswald, Timo Kasper and Pierre Pavlides. The first three attacks come from the first paper and the fourth attack comes from the second paper.

Attack 1

Attack 1 is a nonce replay and length extension attack. This is an attack on a single HiTag2 RFID tag, given a single encrypted nonce and challenge response value pair (nR, aR) for the tag's UID. The attack runs entirely on the RFIDler with it acting like a RWD that replays the same encrypted nonce and challenge response pair for every interaction; this fixes the key stream that the tag's PRNG outputs to the same stream for every interaction.

By brute forcing a subset of the encrypted command space, the RFIDler finds a single valid encrypted command - invalid commands return a known unencrypted error response so finding a valid one is simply a case of trying different values until a response other than the error response is received.

It then bit flips the valid encrypted command to find the other 15 valid encrypted commands. By knowing the contents of page 0 - it's the UID that is presented in clear at the start of each interaction - it tries each encrypyted response in turn, assuming each to be the encrypted version of 'read page 0 non-inverted' and each response to be the encrypted version of page 0.

For each attempted command, it calculates the key stream that would have correctly generated the encrypted command and response: command ++ response XOR key stream = encrypted command ++ encrypted response therefore: key stream = command ++ response XOR encrypted command ++ encrypted response

It then tests the potentially recovered key stream by creating an encrypted command that consumes as much of it as possible, re-initialising with the same encrypyted nonce and challenge response pair (to set the key stream to the same stream as that which produced the encrypted command response it is testing), and then sending this extended encrypted command. If the response is not the error response, then the key stream is valid and the response is the encryption of the page 0 contents (the UID).

When one of the valid encrypted commands satisfies this situation, the recovered key stream must be the output of the PRNG for the given encrypted nonce and challenge response pair.

The RFIDler then uses this key stream to encrypt commands and decrypt the responses, and therefore requests the contents of all 8 pages. Pages 1 and 2 contain the encryption key.

Attack 2

Attack 2 is a time/space trade off to recover the key for situations where the tag has been configured to prevent reading of pages 1 and 2. This attack uses a pre-computed table of 2^37 PRNG states and resultant PRNG output, sorted on the PRNG output. The RFIDler is used to recover 2048 bits of key stream using a modification of attack 1 and this is used to search the table for matching PRNG output. When the output is found, it is tested for validity (by testing previous or following PRNG output) and then the PRNG state is rolled back to the initialisation state, from which the unecrypted nonce and key can be recovered.

Attack 3

Attack 3 is a cryptanalytic attack that focuses on the RWD and a bias in the PRNG output. By capturing 136 encrypted nonce and challenge response pairs, candidates for the first 34 bits of the key can be identified, and for each the remaining 14 bits can be brute forced.

Attack 4

Attack 4 is a fast correlative attack on the key based on a number of captured encrypted nonce and challenge response pairs (up to 32, but 16 usually sufficient). It starts by guessing the first 16 bits of the key and scores all these guesses against how likely they are to be the correct key, given the encrypted nonces and the keystream they should produce. Each guess is then expanded by 1 bit and the process iterates, with only the best guesses taken forward to the next iteration.

Usage details

Attack 1 requires a valid tag and a valid encrypted nonce and challenge response pair. The attacker needs to obtain a valid tag and then use this to obtain a valid encrypted nonce and challenge response pair. This can be acheived by using the RFIDler 'SNIFF-PWM S' command (having previously cleared the nonce storage with 'SNIFF-PWM C'), placing the coil on the RWD and presenting the valid tag. The encrypted nonce and challenge response pairs can then be read out with the 'SNIFF-PWM L' command. These values can then be used to attack the tag with 'HITAG2-CRACK '.

RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM C RFIDler: SNIFF-PWM S Capture encrypted nonce and challenge response pair (nR, aR). RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM L RFIDler: HITAG2-CRACK

Attack 2 requires the same resources as attack 1, plus a pre-computed table. The table can be generated on a disk with >1.5TB of storage, although it takes some time (allow a couple of days). ./ht2crack2buildtable RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM C RFIDler: SNIFF-PWM S Capture encrypted nonce and challenge response pair (nR, aR). RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM L RFIDler: UID RFIDler: HITAG2-KEYSTREAM Copy/paste the key stream to a file. ./ht2crack2search

Attack 3 requires only interaction with the RWD and does not require a valid tag, although it does require a HiTag2 tag that the RWD will initially respond to; e.g. you could potentially use any HiTag2 tag as long as the RWD starts the crypto handshake with it. It requires >=136 encrypted nonce and challenge response pairs for the same tag UID.

RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM C RFIDler: SNIFF-PWM S Capture >=136 encrypted nonce and challenge response pairs (nR, aR). RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM L RFIDler: UID Copy/paste the encrypted nonce and challenge response pairs into a file. ./ht2crack3

Attack 4 requires the same information as attack 3, but only 16-32 encrypted nonce and challenge response pairs are required. ./ht2crack4 -u -n [-N ] [-t ]

Start with -N 16 and -t 500000. If the attack fails to find the key, double the table size and try again, repeating if it still fails.

Once the key has been recovered using one of these attacks, the RFIDler can be configured to operate as a RWD and will capture tags using that key. RFIDler: SET TAG HITAG2 RFIDler: HITAG2-READER

Both the SNIFF-PWM and HITAG2-READER commands can be used as AUTORUN commands for when the RFIDler is powered from a USB power supply without interaction.

RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM C RFIDler: AUTORUN SNIFF-PWM S RFIDler: SAVE Capture encrypted nonce and challenge response pairs. RFIDler: SET TAG HITAG2 RFIDler: SNIFF-PWM L

RFIDler: SET TAG HITAG2 RFIDler: HITAG2-CLEARSTOREDTAGS RFIDler: AUTORUN HITAG2-READER S RFIDler: SAVE Capture tags. RFIDler: HITAG2-COUNTSTOREDTAGS RFIDler: HITAG2-LISTSTOREDTAGS [START] [END]

Tags can be copied with standard RFIDler commands.

RFIDler: SET TAG HITAG2 RFIDler: COPY RFIDler: VTAG Replace original tag with a blank tag. RFIDler: CLONE <blank tag password/key - defaults to 4d494b52>

OR:

RFIDler: SET TAG HITAG2 RFIDler: SET VTAG HITAG2 RFIDler: VWRITE 0 <page 0 contents> RFIDler: VWRITE 1 <page 1 contents> ... RFIDler: VWRITE 7 <page 7 contents> RFIDler: VTAG Place blank tag on coil. RFIDler: CLONE <blank tag password/key - defaults to 4d494b52>

OR:

RFIDler: SET TAG HITAG2 RFIDler: SET VTAG HITAG2 RFIDler: VWRITE 0 <all 8 page contents with no spaces> RFIDler: VTAG Place blank tag on coil. RFIDler: CLONE <blank tag password/key - defaults to 4d494b52>