Various Open Source Cryptographic Libraries are being used these days to implement the general purpose cryptographic functions and to provide a secure communication channel over the internet. These libraries, that implement SSL/TLS, have been targeted by various side channel attacks in the past that result in leakage of sensitive information flowing over the network. Side channel attacks rely on inadvertent leakage of information from devices through observable attributes of online communication. Some of the common side channel attacks discovered so far rely on packet arrival and departure times (Timing Attacks), power usage and packet sizes. Our research explores novel side channel attack that relies on CPU architecture and instruction sets. In this research, we explored such side channel vectors against popular SSL/TLS implementations which were previously believed to be patched against padding oracle attacks, like the POODLE attack. We were able to successfully extract the plaintext bits in the information exchanged using the APIs of two popular SSL/TLS libraries.

1. NOVEL SIDE CHANNELS IN POPULAR
SSL/TLS IMPLEMENTATIONS BASED
ON INSTRUCTION SET ARCHITECTURE
By : Vaishali Garg
1

2. BACKGROUND
2

3. PADDING ORACLE ATTACK
¢ Against CBC-mode encryption with PKCS#5 padding
¢ Oracle exists which on receipt of ciphertext, decrypts it
& replies whether the padding is correct or not
¢ Using this oracle, data can be decrypted without knowing
the key 3
Vaudenay’s Attack
May 2002

4. PADDING ORACLE ATTACK REVIVED
4
Aug 2012
Dec 2014
Jan 2010
Oct 2014

5. ATTACKS BASED ON PACKET
COMPRESSION SIZE
5
Sep 2012
July 2013
(Revival of CRIME)

6. SIDE CHANNEL ATTACKS
¢ Information gained from physical implementation of a
cryptosystem
— Through some observable attributes of an online
communication
¢ Example :
— Packet Arrival & Departure time or an error message
— Packet Size
— Power Usage
6

7. RESEARCH DIRECTION
¢ Side-channel attacks keep on reviving
¢ Such multiple side channels may exist
¢ To determine novel side channels in various open
source SSL libraries such as OpenSSL and wolfSSL
7

8. PADDING ORACLE ATTACK
8

9. PADDING ORACLE ATTACK
9
http://www.bank.com/login.php?message=
b2a72189df804632a55a15d599a1693e6e
62a997052847fd
b2a72189df804632
IV
a55a15d599a1693e
Block 1
6e62a997052847fd
Block 2
https://www.bank.com/login.php?
message=transfer10x06x06x06x0
6x06x06
3-DES, AES,
RSA etc.

10. PADDING ORACLE ATTACK
10
6e 62 a9 97 05 28 47 fd
Decrypt
??
?? ?? ?? ?? ?? ?? ?? 01
Intermediate block
Previous block
Plaintext block
IV
?? ?? ?? ?? ?? ?? ?? ??
00 00 00 00 00 00 00
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ??
??00 00 00 00 00 00 00
??
Decrypt
Block 1 Block 2
Valid padding check

11. PADDING ORACLE ATTACK
11
Incorrect paddingCorrect padding
Response time - more Response time - less
Further
decryption
takes place
No Further
decryption

12. 6e 62 a9 97 05 28 47 fd
Decrypt
??
?? ?? ?? ?? ?? ?? ?? 01
Intermediate block
Previous block
Plaintext block
IV
?? ?? ?? ?? ?? ?? ?? ??
00 00 00 00 00 00 00
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ??
??00 00 00 00 00 00 00
??
Decrypt
means, A XOR B = 0x01
?? XOR ?? = 01
PADDING ORACLE ATTACK
12
Block 1 Block 2
Brute
force

13. ¢ Brute Force the Last Byte – from 0x00-0xff
13
The
Oracle
00 00 00 00 00 00 00
6e 62 a9 97 05 28 47 fd
00
C1
C2
64 32 1b b8
0a aa 08 39
P2
Incorrect padding,
immediate server
response
Error 404 : Server
not found :(
The
Oracle
00 00 00 00 00 00 00
6e 62 a9 97 05 28 47 fd
39
C1
C2
64 32 1b b8
0a aa 08 01
P2
Correct padding,
server response
takes some time
Error 404 : Server
not found :(
01
39

14. PADDING ORACLE ATTACK
14
Server Response
Server Response Time
(same in all cases)
(different for valid padding case)

15. PADDING ORACLE ATTACK
So, C2’ xor C1 = 0x01
C2’ xor 0x39 = 0x01
implies, C2’ = (0x39) xor (0x01)
C2’ = 0x38 (intermediate byte of C2)
---- (1)
6e 62 a9 97 05 28 47 fd
Decrypt
?? ?? ?? ?? ?? ?? ?? 01
IV
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ?? ?
?
???? ?? ?? ?? ?? ?? ??
39
00 00 00 00 00 00 00
00 00 00 00 00 00 00 39
Decrypt
means, C2’ XOR C1 = 0x01
?? XOR 39 = 01
C1 = a55a15d599a1673e ---(2)
C2 = 6e62a997052847fd
15
From CBC Decryption
P2 = (Intermediate byte of C2) xor (C1)
P2 = (0x38) xor (0x3e)
P2 = 0x06
Hence, Plaintext is successfully obtained
C1 C2

16. Big Question
16

17. Are these the only side channels?
Or Can there be other instruction set architecture based
side channels?
17

18. EXAMPLES
¢ Some instructions are executed more often for valid
padding
¢ Example :
— CPU cycles
— Memory Accesses
18

19. CONTRIBUTION
¢ Explored Novel Side Channels on OpenSSL & wolfSSL
— Based on Instruction Set Architecture
— Examples : CPU cycles, Memory Accesses etc.
¢ Successful decryption of cipher text using
aforementioned side channels
— Change in the value of the attributes
— Clearly Observable for correct plaintext value
— Decipher all bytes
19

20. OPENSSL
20

21. OPENSSL
— Full featured open source toolkit
— Implements SSL(v2/v3) & TLS protocols(v1)
— Support for various cryptographic functions
— Used id Open Source Projects like TOR, IPSEC Tools, APT package
manager
21
Source :
http://arstechnica.com/security/2014/04/critical-crypto-bug-in-openssl-opens-two-

22. RESEARCH APPROACH
22

23. Research Approach
255
ciphertext
variants
Attributes
Data
128-bit AES
encryption
Ciphertext
GEM5 simulator
AES decryption
static binary Statistical Analysis
User
Actual System
23

24. GEM5 SIMULATOR
¢ Computer system simulation platform
¢ Supports various ISAs : Alpha, ARM, MIPS, Power, SPARC,
and x86
¢ Two modes :
— System Emulation :
¢ Used for running individual applications or set of applications
¢ Used if you want do research on a particular application
— Full System Emulation :
¢ Used For booting OS
¢ Used if you want to do research on how does the OS effects our
application or devices
¢ Stats for Instruction Set Architecture related attributes
such as :
— Instructions committed
— Integer register reads & writes
— ALU accesses
— Arithmetic operations completed & many more… 24

25. IMPLEMENTATION AND
EVALUATION
25

26. OPENSSL
OpenSSL
Desktop Mobile Stock
26
PERL (CPAN)

27. 00000000000000000000000000000000 dc95342e176fe8f26e62a997052847fd
00000000000000000000000000000001 dc95342e176fe8f26e62a997052847fd
00000000000000000000000000000002 dc95342e176fe8f26e62a997052847fd
000000000000000000000000000000ff dc95342e176fe8f26e62a997052847fd
Attack Approach – On AES-128 bit
27
Plaintext : zmx4wker02g6HELLOHOWSUqA (24 bytes)
zmx4wker02g6HELLOHOWSUqAx08x08x08x08x08x08x08x08x08(32 bytes)
Ciphertext : 52cb50912065ac52a55a15d599a16930dc95342e176fe8f26e62a997052847fd
(32 bytes)
GEM5 simulator
128-bit AES
decryption static
binary

28. OPENSSL RESULTS
28

29. OPENSSL RESULTS
¢ For Last Byte
29
205471
205472
205473
205474
205475
205476
205477
00.log
06.log
0c.log
12.log
18.log
1e.log
24.log
2a.log
30.log
36.log
3c.log
42.log
48.log
4e.log
54.log
5a.log
60.log
66.log
6c.log
72.log
78.log
7e.log
84.log
8a.log
90.log
96.log
9c.log
a2.log
a8.log
ae.log
b4.log
ba.log
c0.log
c6.log
cc.log
d2.log
d8.log
de.log
e4.log
ea.log
f0.log
f6.log
fc.log
No.ofInteger
Multiplications
Last Byte
Integer Multiplications
At last byte = 0x39

30. OPENSSL RESULTS
¢ For Second Last Byte
30
98594000
98595000
98596000
98597000
98598000
98599000
98600000
98601000
98602000
00.log
06.log
0c.log
12.log
18.log
1e.log
24.log
2a.log
30.log
36.log
3c.log
42.log
48.log
4e.log
54.log
5a.log
60.log
66.log
6c.log
72.log
78.log
7e.log
84.log
8a.log
90.log
96.log
9c.log
a2.log
a8.log
ae.log
b4.log
ba.log
c0.log
c6.log
cc.log
d2.log
d8.log
de.log
e4.log
ea.log
f0.log
f6.log
fc.log
No.ofInteger
RegisterReads
Second Last Byte
Integer Register Reads
At second last byte = 0x63

31. REASON FOR VARIATION
31
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

32. WOLFSSL
32

33. WOLFSSL
— Lightweight embedded SSL library (20 times smaller than
OpenSSL)
— Small footprint size(30-100kB) & low runtime memory
usage(3-36kB)
— Targeted for embedded devices, RTOS & environments
facing constraints in computational resources
— Major uses in MySQL, wireless sensors used in power
grids etc.
33

34. Various Projects using wolfSSL Products
34

35. 00000000000000000000000000000000 5145ea93c3b647860c13228d8dc1e90c
Attack Approach – On AES–128 bit
35
Plaintext : POST/gp/redirect/indi.htmlCookie:token=wdH (42 bytes)
POST/gp/redirect/indi.htmlCookie:token=wdHx06x06x06x06x06x06(48 bytes)
Ciphertext :
c5421b878c2d36a052f45796ad1bdea11d501312a305f586369cd8e19136db095145ea93c3b6
47860c13228d8dc1e90c (48 bytes)
GEM5 simulator
128-bit AES
decryption static
binary
00000000000000000000000000000001 5145ea93c3b647860c13228d8dc1e90c
00000000000000000000000000000002 5145ea93c3b647860c13228d8dc1e90c
000000000000000000000000000000ff 5145ea93c3b647860c13228d8dc1e90c

36. WOLFSSL RESULTS
¢ For Last Byte
36
448100000
448120000
448140000
448160000
448180000
448200000
00.log
07.log
0e.log
15.log
1c.log
23.log
2a.log
31.log
38.log
3f.log
46.log
4d.log
54.log
5b.log
62.log
69.log
70.log
77.log
7e.log
85.log
8c.log
93.log
9a.log
a1.log
a8.log
af.log
b6.log
bd.log
c4.log
cb.log
d2.log
d9.log
e0.log
e7.log
ee.log
f5.log
fc.log
No.ofIntegerRegister
Reads
Last Byte
Integer Register Reads
At a value where plaintext
byte becomes 0x00

37. POODLE ATTACK
37

38. POODLE ATTACK
¢ Attacker’s interest is in secret token or cookie
CSRF Attack
38

39. POODLE ATTACK
¢ An encrypted post request looks as follows :
¢ An attacker can control both the request path & the request
body
¢ Hence, he can generate requests such that following two
conditions hold :
a) The padding fills an entire block (encrypted into Cn).
b) The cookies’ first as of yet unknown byte appears as the final byte
in an earlier block (encrypted into Ci).
POST /path Cookie: name=value...rnrnbody || 20byte MAC || padding
39

40. POODLE ATTACK
¢ Example
original plaintext :
POST/gp/redirect/indi.htmlCookie:token=wdHZJaxBe……….
Attacker can modify this plaintext
size as multiple of block size (say 8)
& hence the padding will fill one
complete last block which encrypts
into Cn
48 Bytes
First Condition fulfilled
40

41. POODLE ATTACK
¢ To fulfill the second condition the plaintext is changed in this
manner :
Encrypts into Ci-1 Encrypts into Ci
Iteration 1
Iteration 2
Iteration 3
Iteration 4
41
Unknown byte appears as Final byte of a 8 byte block

42. POODLE ATTACK
¢ Cipher text corresponding to First Iteration :
¢ Replace Cn with Ci
Ciphertext :
5f06fc6cc5ff7b230fdcf40b1d0603ca0067df2ec6a8f3be0067df2ec6a8f3be5c48fe596cca889fb4e07a
3571aac7ad26b8d80ac480904bb075cbf233b4d6298bf5816a3d3dca5fa7d5261e44b0ce4a545f13718
8deb3a49446a30343a09e38a73b3e45bd96efbb
Cn Ci
Ciphertext :
5f06fc6cc5ff7b230fdcf40b1d0603ca0067df2ec6a8f3be0067df2ec6a8f3be5c48fe596cca889fb4e07a
3571aac7ad26b8d80ac480904bb075cbf233b4d6298bf5816a3d3dca5fa7d5261e44b0ce4a545f13718
8deb3a49446a30343a09e385c48fe596cca889f
Cn / Ci
Ci-1
Ci-1 42

43. POODLE ATTACK
43
0000000000000000 5c48fe596cca889f GEM5 simulator
3-DES decryption static
binary
0000000000000001 5c48fe596cca889f
0000000000000002 5c48fe596cca889f
00000000000000ff 5c48fe596cca889f

44. WOLFSSL RESULTS
44

45. WOLFSSL RESULTS
¢ For Last Byte
45
122525000
122530000
122535000
122540000
122545000
122550000
122555000
00.log
07.log
0e.log
15.log
1c.log
23.log
2a.log
31.log
38.log
3f.log
46.log
4d.log
54.log
5b.log
62.log
69.log
70.log
77.log
7e.log
85.log
8c.log
93.log
9a.log
a1.log
a8.log
af.log
b6.log
bd.log
c4.log
cb.log
d2.log
d9.log
e0.log
e7.log
ee.log
f5.log
fc.log
No.ofMemory
References
Last Byte
Memory References
Maximum value at byte = 0xc9

46. POODLE ATTACK
So, Cn’ xor Cn-1 = 0x00
Cn’ xor 0xc9 = 0x00
implies, Cn’ = (0xc9) xor (0x00)
Cn’ = 0xc9 (intermediate byte of Cn/Ci)
5c 48 fe 59 6c ca 88 9f
Decrypt
?? ?? ?? ?? ?? ?? ?? 00
IV
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ?? ??
?? ?? ?? ?? ?? ?? ?? ?
?
???? ?? ?? ?? ?? ?? ??
39
00 00 00 00 00 00 00
00 00 00 00 00 00 00 39
Decrypt
means, Cn’ XOR Cn-1 = 0x01
?? XOR 39 = 00
Ci-1 = 0067df2ec6a8f3be
Ci/Cn = 5c48fe596cca889f
46
From CBC Decryption
Pi = (Intermediate byte of Ci) xor (Ci-1)
Pi = (0xc9) xor (0xbe)
Pi = 0x77 [Hex value for ‘w’]
Hence, cookie’s first unknown byte is
revealed
Cn-1 Cn / Ci

47. WOLFSSL RESULTS
¢ For Second Last Byte
47
246070000
246080000
246090000
246100000
246110000
246120000
246130000
246140000
00.log
07.log
0e.log
15.log
1c.log
23.log
2a.log
31.log
38.log
3f.log
46.log
4d.log
54.log
5b.log
62.log
69.log
70.log
77.log
7e.log
85.log
8c.log
93.log
9a.log
a1.log
a8.log
af.log
b6.log
bd.log
c4.log
cb.log
d2.log
d9.log
e0.log
e7.log
ee.log
f5.log
fc.log
No.ofcommitted
instructions
Second Last Byte
Committed CPU Instructions
Maximum value at byte = 0xf1

48. REASON FOR VARIATION
48
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

49. TAKEAWAYS
¢ Many Side-channels have effected cryptographic libraries
— These side channels have revived very often
— Instruction based side channels haven’t been explored
¢ OpenSSL and wolfSSL previously patched against padding
oracle and POODLE attack
¢ We explored novel side-channels on popular SSL/TLS
Implementations – eg. Memory accesses, CPU instructions
etc.
¢ Successfully decipher all plaintext bytes
49

50. FUTURE WORK
¢ We performed it in simulation environment which has
its own bottleneck. Other tool which can give faster
results can be used.
¢ We have used one API for OpenSSL & wolfSSL. Other
APIs can be explored.
¢ Other cryptographic Libraries can be explored.
¢ Real Life Applications can be studied
50

51. REFERENCES
— Ivanov, A. (2005). Side-Channel Attacks.
— Skorobogatov, Sergei. "Side-channel attacks."
— Lomne, Victor, et al. "Side Channel Attacks." Security Trends for FPGAS.
Springer Netherlands, 2011. 47-72.
— Peeters, Eric, et al. "Improved higher-order side-channel attacks with
FPGA experiments." Cryptographic Hardware and Embedded Systems–CHES 2005.
Springer Berlin Heidelberg, 2005. 309-323.
— Black, John, and Hector Urtubia. "Side-Channel Attacks on Symmetric
Encryption Schemes: The Case for Authenticated Encryption." USENIX
Security Symposium. 2002.
— Vaudenay, Serge. "Security Flaws Induced by CBC Padding—Applications
to SSL, IPSEC, WTLS..." Advances in Cryptology—EUROCRYPT 2002. Springer
Berlin Heidelberg, 2002.
— Paterson, Kenneth G., and Arnold Yau. "Padding oracle attacks on the
ISO CBC mode encryption standard." Topics in Cryptology–CT-RSA 2004.
Springer Berlin Heidelberg, 2004. 305-323.
— Yau, Arnold KL, Kenneth G. Paterson, and Chris J. Mitchell. "Padding
oracle attacks on CBC-mode encryption with secret and random
IVs." Fast Software Encryption. Springer Berlin Heidelberg, 2005.
— Rizzo, Juliano, and Thai Duong. "Practical Padding Oracle
Attacks." WOOT. 2010.
— Duong, Thai, and Juliano Rizzo. "Padding oracles everywhere." (2010).
51

52. REFERENCES
— Kaliski, Burt. "PKCS# 7: Cryptographic Message Syntax Version 1.5." (1998).
— Möller, Bodo, Thai Duong, and Krzysztof Kotowicz. "This POODLE Bites:
Exploiting The SSL 3.0 Fallback." (2014).
— Binkert, Nathan, et al. "The gem5 simulator." ACM SIGARCH Computer
Architecture News 39.2 (2011): 1-7.
— Gluck, Yoel, Neal Harris, and Angelo Prado. "BREACH: reviving the CRIME
attack."
— Irazoqui, Gorka, et al. "Lucky 13 Strikes Back." Proceedings of the 10th
ACM Symposium on Information, Computer and Communications Security.
ACM, 2015.
— Blatz, Jeremiah. "CSRF: Attack and Defense." McAfee® Foundstone®
Professional Services, White Paper (2007).
— Johny, Alphonsa. "Secure Socket Layer Implementations-A."
— Kumar, Uday, Tuhin Borgohain, and Sugata Sanyal. "Comparative Analysis of
Cryptography Library in IoT." arXiv preprint arXiv:1504.04306 (2015).
— Krawczyk. " The Order of Encryption and Authentication for Protecting
Communications." CRYPTO 2001
— Juliano Rizzo, Thai Duong."Here Come The Ninjas."Ekoparty 2011
— Juliano Rizzo, Thai Duong."The CRIME Attack."Ekoparty 2012
52

53. THANK YOU
53