1. Using the CC2420 with AES Support
Eric Famiglietti and Simone Willett

2. WSN Encryption Issues Lack of physical protection Resource constraints
Public-key cryptography, RSA
Unsuitable for low power and limited memory
Key establishment/distribution problem
Symmetric-key algorithms

3. WSN Encryption Examples
Identity-based encryption
Solves problem of public-key exchange
RSA, Elliptic curve cryptography
wsn-security-survey.pdf
TinySec
DES, RC5, Skipjack, AES

4. AES Advanced Encryption Standard Symmetric key encryption standard
Successor of DES
Symmetric key encryption standard
Used worldwide
Fixed block size of 128 bits
Key size of 128, 192, or 256 bits
Number of rounds of encryption
10, 12, 14 respectively

5. AES: Performance Faster in hardware
Good performance was an explicit goal
Performs well on a variety of hardware

6. Trust Management
We are primarily concerned with authorization, as opposed to authentication.
Authentication is the mechanism whereby systems may securely identify their users.
Authorization is the mechanism by which a system determines what level of access a particular authenticated user should have to secured resources controlled by the system.
Obviously a real implementation of authorization will depend on authentication

7. Trust Management, the bottomline

8. Main Goal
We would like to set up a public key encryption to authorize the sender and receiver then establish AES session keys.
Verification takes 2 minutes. - unrealistic
Sprocket currently works with software created AES keys that are sent across the air and verified by the nodes.
Do all AES encryption on the chip.

9. Trust Mangement = RT0
Flexible approach to access control in distributed systems
Access control decisions are based on the policy statements, called credentials,
Permissions in RT0 are represented by roles.
Credentials are made by different principals and stored in a distributed manner

10. Credential A credential is a statement Requirements:
Signed by the issuer
About a subject
Containing info about the subject.
Requirements:
Unforgeable.
Verifiable (belongs to the entity asking for the service)
Signed
Have well defined semantics.

11. Example

13. Certificate Contains credential information in an over the air format.
A role A.r denotes the set of entities that are members of it.
Example: UVM.studentId Alice
Entities can define roles, issue credentials, and make requests.
In our case identities are pubic keys.

14. Certificate Validity
Credentials contain private information and should be treated as such (e.g. medical record).
Since an authorizer receives certificates from an unknown potentially untrustworthy entities, the validity must be checked
Signatures
Certificate must not have expired.

15. Show Verify Example Form 1 is A.r  E Form 1 Public Key 40 bytes.
Role 1
Pub Key2 40 bytes.
Signature 2(21) = 42 bytes.
Total 124 bytes.

16. Project
Currently symmetric keys are being used to encrypt with software.
We want to use the hardware to make this a faster process.
CC2420 chip that has AES support.
Allow for multiple keys and decryption
Many motes talking at once

17. Steps Use the hardware version of AES in a simple Blink program.
Use hardware AES to send and receive packets that are encrypted.
Integrate into the overall project.
Test and optimize.

18. Encryption on CC2420 Use Hardware security in CC2420.
The encryption provides a plain AES encryption, with 128 bit plaintext and 128 bit keys.
To encrypt a plaintext, a node first writes the plaintext to the stand-alone buffer SABUF, and issues a SAES command to initiate the encryption.
When encryption is complete, the ciphertext is written to the buffer, overwriting the plaintext.

19. Interfaces interface CC2420Register as SECCTRL0;
interface CC2420Ram as KEY0;
interface CC2420Ram as SABUF;
interface CC2420Strobe as SAES;
interface CC2420Strobe as SNOP;

20. How to start First power up the chip. Initialize the key. Encrypt.
Send
Decrypt.

21. Show AES Standalone example

22. References
des.pdf.
Theory.stanford.edu/~ninghui/talks/rt_oakland02_slides .pdf.
Cis.sjtu.edu.cn/…/The_Standalone_AES_Encryption_o f_CC2420_(TinyOS_2.10_and_MICAz)