1.  Insecure Connection Bootstrapping in Cellular Networks: The Root of All Evil
Syed Rafiul Hussain*, Mitziu Echeverria†, Ankush Singla*,
Omar Chowdhury†, Elisa Bertino* Purdue University, University of Iowa

2. Initial Connection Setup with a Base Station in 4G and 5G Networks
Time & Frame Synchronization
System Info. Block
Master info. Block
Frame Synch.

3. Fake Base Station in 4G and 5G Networks
How can we prevent cellular devices from connecting to Fake Base Stations?
IMSI Response
Authentication Reject
Registration Reject
IMSI Request
IMSI: International Mobile Subscriber Identity

4. Potential Defense Techniques Against Fake Base Station
Attack Specific Defense Prevent Spoofing of Individual Messages
Generic Defense
Prevent Spoofing of Broadcast Messages
IMSI Request
Registration Reject
Authentication Reject
IMSI Request
Registration Reject
Authentication Reject

5. Preventing Broadcast Spoofing
Symmetric Key Based Broadcast Authentication
TESLA-based Broadcast Authentication
msg 2, MAC2, Key 1
Secure Channel
msg 3, MAC3, Key 2
Secure channel establishment
Delayed key disclosure

6. 1. Certificate chain length 2. Certificate Revocation
PKI-based Mechanism
MME UE
Base Station
Core Network
1. Certificate chain length
2. Certificate Revocation
3. Signature Generation Overhead
4. MitM Relay
Self-signed
MME-signed
CN-signed
MIB, 𝐒𝐈 𝐆 𝐁𝐒 , 𝐜𝐞𝐫 𝐭 𝐌𝐌𝐄 , 𝐜𝐞𝐫 𝐭 𝐂𝐍
SIB1, 𝐒𝐈 𝐆 𝐁𝐒 , 𝐜𝐞𝐫 𝐭 𝐌𝐌𝐄 , 𝐜𝐞𝐫 𝐭 𝐂𝐍 6

7. Optimized PKI Scheme (1/3)
A Lightweight Design of Certificate for Cellular Network
Propose a specialized certificate format
Base Station’s Public Key
Cell ID
location
expiration time
signature of MME

8. Protocol-Level Optimizations
Which messages require authentication?
Which SIBs require authentication?
Frame Synch.
Sys. Info. Block Type 1
Master info. Block
Sys. Info. Block Type 2
System Info. Block
Minimize certificate chain’s transmission
SIB 1,
SIGN_SIB1
CERT CHAIN
SIB2, SIGN_SIB2
Aggregating Authentication

9. Cryptographic Scheme-level Optimization
Reduce the size of the signatures
Aggregate SIGN
SIB1,
SIGN_BS, SIGN_MME, SIGN_CN
Compute the expensive crypto operations at offline

10. Countermeasure for Relay Attacks
Distance Bounding Protocol
Allow a bootstrapping message to be valid for a short time
SIB1, Aggregate SIGN, Timestamp, ∆t, location
t rcvd − t gen < ∆ t

11. Evaluation Results
End-to-end delay induced by different digital signature schemes against baseline

12. Conclusion Prevents devices to connect to malicious base stations.
Moderate Overhead (Max: 220 bytes, 28 ms).
Backward compatibility.

13. Thank You

14. Syed Rafiul Hussain Purdue University hussain1@purdue.edu
Insecure Connection Bootstrapping in Cellular Networks: The Root of All Evil
Syed Rafiul Hussain
Purdue University