Guest Lecture at Universitat Autonoma Barcelona about Symmetric Key Cryptography

1. Symmetric Key Cryptography
Setia Juli Irzal Ismail
ID-CERT – Telkom University

2. 1. Introduction
2. Introduction about AES
3. Attack in Symmetric Cryptography
4. Cryptography in Malware
5. Discussion

3. Introduction
• Setia Juli Irzal Ismail
• Jul Ismail
• Malware Analyst – ID-CERT
• Lecturer – Telkom University
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4. ID-CERT
• Indonesia Computer Emergency Response Team
• 1998 – Dr. Budi Rahardjo
• Community based
• Incident Handling
• Malware Lab
• Research & Training about Malware
• Tools: Malware Scanner
• Founder AP-CERT: JP-CERT & AusCERT
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5. Indonesia
• South East Asia
• 7th largest Country –
• 1,904,569 square km2
• Archipelago
• 13000 Islands
• 4th: Population; 261 million
• 700 local language

6. AES

7. AES
• Advanced Encryption Standard (AES) was published by the
National Institute of Standards and Technology (NIST) in
2001.
• NIST is a Agency in USA; measurement standard Laboratory
• replace DES (Data Encryption Standard) – 1977 (IBM)
• have theoretical attacks that can break it
• have demonstrated exhaustive key search attacks
• slow
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8. Selection Process
• US NIST issued call for ciphers in 1997
• Open Competition
• 15 candidates accepted in Jun 98
• investigated by cryptographers;
• Security,
• performance in different PC architecture
• Implementation in limited environment (smart cards
limited memory, low gate count implementations, FPGAs)

9. Finalist
• 1999: 5 Finalist
• MARS, RC6, Rijndael, Serpent, and Twofish.
• 2000: Rijndael
• official standard by publishing an announcement in the Federal
Document
• Positive comment for opennes from the community
• Bruce Schneier (Twofish) “I have nothing but good things to say about
NIST and the AES process“
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10. Rijndael
• developed by two Belgian cryptographers,
• Vincent Rijmen and Joan Daemen,
• all operations are performed on 8-bit
• Finite Field Arithmetic
• each with a block size of 128 bits, but three different key lengths: 128,
192 and 256 bits
• Substitution & Permutation
• Repetition 10 round for 128 bit keys, 12 à 192; 14 à256

11. Encryption process
1. Plaintext data to be encrypted
2. Static bytes that are part of the algorithm (lookup table)
3. The key used for encryption
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12. Encryption process
• Substitution & Permutation
• Add key
• Shift rows
• Substituting bytes
• Mix columns
• Repetition 10 round for 128 bit keys, 12 à 192; 14 à256
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13. Implementation
• RAR, Winzip, 7z
• NTFS
• Bitlocker, Truecrypt
• IEEE 802.11 Wireless
• Whatsapp, Facebook Messenger
• IPSec à VPN
• GPG à
• Intel & AMD Processor
• Grand Theft Auto

14. Security Concern

15. Bruteforce
• Trying all possible combination
• =exhaustive key search
• Needs big computing power & energy
• 128 bit key AES à1,02 x1018 years
• 256-bit à 3,31 x 1056 years
• billions of years to brute force
• Supercomputer
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16. Attack - Cryptanalyst
• 2002; XSL attack;
• Theoretical attack ; Courtois and Pieprzyk à unworkable
• 2009: Alex Biryukov, Dmitry Khovratovich, and Ivica Nikolić,
• 2011; Bogdanov, Khovratovich, and Rechberger,
• Snowden; NSA doing research on attack based on TAU
statistic
• Without key à No success (if AES correctly implemented)

17. Side Channel Attack
• Not on cipher text
• find a weakness in the implementation
• Hardware/software
• measure power consumption, electromagnetic emissions,
and heat generation
• requires physical access to the target device.
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18. Success story
• 2005: Bernstein ; cache-timing attackà OpenSSL
• number of machine cycles taken by the encryption operation
• 2009: DFA (Differential Fault Analysis) à hardware (key
recovery)
• Smart Card à embedded processor ;
• Overclocking, high temperature à false output

19. Key Exchange Problem
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20. Malware

21. Crypto implementation in malware
• Encrypt the source code à difficult to reverse
• Encrypt the comunication to C&C server
• Ransomware

22. Ransomware
• Malware encrypt your data
• Ask ransom (money)
• Different crypto algorithm
• Most common : asymmetric encryption
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23. Ransomware-File obfuscation
• move or hide targeted files;
• show ransom message
• Reverse the code à hide the file

24. Custom crypto
• Algorithm to encrypt the file
• XOR the file
• Algorithm is the key
• Reverse the steps
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25. MBR rewriting
• Master Boot Record
• Rewrite MBR à require password or number
• Force reboot a computer à before windows load à ransom
message
• reversing the serial or password validation algorithm: MBR
• Keygen

26. Asymmetric – modern ransomware
1. dynamically generates the keys locally
• Sends to C&C server à client ID
• Keys are not identical
2. Keys are generated by author
• Preloaded in the ransomware
• Key are static
• Someone get the key,
• Share the key
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27. Dynamic generated keys
• Analyse memory dump for file recovery
• cryptanalyst
• Intercept the transfer and generation of the keys

28. Ransomware Algorithm
• AES
• RSA
• Blowfish
• etc
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29. Shione Ransomware case
• C#
• Keys are embedded in the ransomware
• RSA & AES
• AES à encrypt victim files
• AES Key à RSA
• Public Key RSA embedded in the malware

30. Reference
• William, S., & Stalling, C. (2006). Network Security, 4/E.
• Malware analysis report, ID-CERT

31. Terima Kasih
jul [at] tass.telkomuniversity.ac.id
jul_ismail
Blog: julismail.staff.telkomuniversity.ac.id
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