1. Why Client Side Storage?
Where to store?
How to store secure?
Conclusion
Client Side Secure Storage
Scalability for free
Dominik G¨tjens
a
Computer Science and Media
Hochschule der Medien, Stuttgart
27. January 2012
Dominik G¨tjens
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2. Why Client Side Storage?
Where to store?
How to store secure?
Conclusion
Agenda
1 Why Client Side Storage?
Sessions are a workaround
Sessions scale very bad
Scaling at no cost
2 Where to store?
Client Side Capabilities
Transmission Performance
Client Side Scaling
3 How to store secure?
Encrypt Data
Signatures
Message Authentication Codes
4 Conclusion
Conclusion
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3. Why Client Side Storage?
Sessions are a workaround
Where to store?
Sessions scale very bad
How to store secure?
Scaling at no cost
Conclusion
Agenda
1 Why Client Side Storage?
Sessions are a workaround
Sessions scale very bad
Scaling at no cost
2 Where to store?
Client Side Capabilities
Transmission Performance
Client Side Scaling
3 How to store secure?
Encrypt Data
Signatures
Message Authentication Codes
4 Conclusion
Conclusion
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4. Why Client Side Storage?
Sessions are a workaround
Where to store?
Sessions scale very bad
How to store secure?
Scaling at no cost
Conclusion
HTTP is stateless
”HTTP is a stateless protocol. A stateless protocol does not
require the server to retain information or status about each
user for the duration of multiple requests.”
– Wikipedia –
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5. Why Client Side Storage?
Sessions are a workaround
Where to store?
Sessions scale very bad
How to store secure?
Scaling at no cost
Conclusion
HTTP Sessions are a Workaround, arent they?
HTTP is build on a stateless approach
no connection indicator
when does a session start? when does it end?
⇒ sessions can only be closed by timeout
Every open session consumes memory
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6. Why Client Side Storage?
Sessions are a workaround
Where to store?
Sessions scale very bad
How to store secure?
Scaling at no cost
Conclusion
Server Side State
Client A Server
Memory
Client B
Session A
Client C Session B
Session C
Client D
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7. Why Client Side Storage?
Sessions are a workaround
Where to store?
Sessions scale very bad
How to store secure?
Scaling at no cost
Conclusion
Sessions scale very bad
No simple adding of machines
You have to guarantee that one user always lands on the same
machine
Or you have to implement a complex multi-machine session
storage
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8. Why Client Side Storage?
Sessions are a workaround
Where to store?
Sessions scale very bad
How to store secure?
Scaling at no cost
Conclusion
Scaling at no cost
Build your webserver like a webservice:
The client brings the data
The server application consists of several independet functions
Functions are without side effects
so you get an easy stateless webserver which you can simply upgrade
through adding machines
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9. Why Client Side Storage?
Client Side Capabilities
Where to store?
Transmission Performance
How to store secure?
Client Side Scaling
Conclusion
Agenda
1 Why Client Side Storage?
Sessions are a workaround
Sessions scale very bad
Scaling at no cost
2 Where to store?
Client Side Capabilities
Transmission Performance
Client Side Scaling
3 How to store secure?
Encrypt Data
Signatures
Message Authentication Codes
4 Conclusion
Conclusion
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10. Why Client Side Storage?
Client Side Capabilities
Where to store?
Transmission Performance
How to store secure?
Client Side Scaling
Conclusion
Client Side Capabilities
Cookies
RFC 2965: min. 20 Cookies a 4kb = 80kb pro Domain
Firefox 2,3 and IE7 supports 50 cookies a 4kb = 200kb
Flash-Cookies unlimited storage
HTML-Markup e.g.
hidden fields
Javascript-RAM
HTML5 Storage
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11. Why Client Side Storage?
Client Side Capabilities
Where to store?
Transmission Performance
How to store secure?
Client Side Scaling
Conclusion
Transmission Performance
1000 ms
935 ms
900 ms
800 ms
Typical Roundtrip Times
700 ms
598 ms 100BaseT 1ms
600 ms
WLAN 10ms
500 ms DSL-6000 40ms
400 ms DSL-2000 55ms
297 ms ISDN 200ms
300 ms
209 ms
200 ms 145 ms
112 ms
100 ms 76 ms 82 ms
ms
1 kB 2 kB 8 kB 16 kB 32 kB 128 kB 512 kB 1024 kB
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12. Why Client Side Storage?
Client Side Capabilities
Where to store?
Transmission Performance
How to store secure?
Client Side Scaling
Conclusion
Client Side State
Client A Server
Session A
Memory
Client B
Session B
Client C
Session C
Client D
Session D
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13. Why Client Side Storage?
Client Side Capabilities
Where to store?
Transmission Performance
How to store secure?
Client Side Scaling
Conclusion
Client Side State
Server
Method
Method
Client State Data Check integrity
Method
Method
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14. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
Agenda
1 Why Client Side Storage?
Sessions are a workaround
Sessions scale very bad
Scaling at no cost
2 Where to store?
Client Side Capabilities
Transmission Performance
Client Side Scaling
3 How to store secure?
Encrypt Data
Signatures
Message Authentication Codes
4 Conclusion
Conclusion
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15. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
Encrypt Data
Client can’t manipulate encrypted data without knowledge of
encryption-key
but Client can’t even read encrypted data without encryption-key
Security is the same as the use Encryption-Algorithm and Key
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16. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
Signature
Don’t crypt data, just sign them
Most Webserver have SSL-Certificates
Use your private key to sign client-saveed data
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17. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
Signature
1000 Samples with DSA
7
6
5 Complexity independent
from Datasize
4
DSA Sign Verrification consumes a lot
3 DSA Verify
of CPU-Time
2
1
0
512 B 1 KB 4 KB 1MB
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18. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
HMAC
HMAC = Keyed-Hash Message Authentication Code
a cryptographic secure message authentication
hmac = H(K ⊕ opad, H(K ⊕ ipad, text))
K = Key
B = Blocksize
opad = 0x5C repeated B times
ipad = 0x36 repeated B times
Popular cryptographic functions are SHA1 and MD5
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19. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
MD5 vs. SHA1
MD5 is faster than SHA1, isn’t it?
1
Digest Perfomance in MegaBytes per Second
Pentium P5 90MHz Power Mac 80MHz SPARC 4 110 MHz
MD5 13.1 3.1 5.1
SHA1 2.5 1.2 2.0
1
Bob Baldwin, RSA Data Security Inc. (1996)
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20. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
HMAC Perfomance
1000 Samples with HMAC-SHA1 and HMAC-MD5
0,12
0,1
0,08
0,06 SHA-1
MD5
0,04
0,02
0
512 B 1 KB 4 KB 1MB
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21. Why Client Side Storage?
Encrypt Data
Where to store?
Signatures
How to store secure?
Message Authentication Codes
Conclusion
HMAC Perfomance
1000 Samples with HMAC-SHA1 and DSA
10
9
8
7
6
5 HMAC_SHA1
DSA Signatur
4
3
2
1
0
512 B 1 KB 4 KB 1MB
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22. Why Client Side Storage?
Where to store?
Conclusion
How to store secure?
Conclusion
Agenda
1 Why Client Side Storage?
Sessions are a workaround
Sessions scale very bad
Scaling at no cost
2 Where to store?
Client Side Capabilities
Transmission Performance
Client Side Scaling
3 How to store secure?
Encrypt Data
Signatures
Message Authentication Codes
4 Conclusion
Conclusion
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23. Why Client Side Storage?
Where to store?
Conclusion
How to store secure?
Conclusion
Conclusion
Don’t store Information in the server session if there is any chance
that you have to scale
Compute HMAC-SHA1 over data that shouldn’t be alterted by
the client
If your Datasize is low use Cookies
If your Datasize is medium use Cookies but be sure they wont be
transmitted with every request
If your Datasize is high youse signed HTML5-Storage or flash
cookies
Cryptographic Client Side Storage as secure as
HTTP-Sessions
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24. Why Client Side Storage?
Where to store?
Conclusion
How to store secure?
Conclusion
The End
Keep your state less
Further questions or discussion? Contact me at:
E-Mail: info@dominik-gaetjens.de
Xing: http://xing.to/gaetjens
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