1. The Design of E-Traveler’s Check with Efficiency and Mutual Authentication
Chair Professor Chin-Chen Chang
Feng Chia University
National Chung Cheng University
National Tsing Hua University

2. Outline
Introduction
Proposed scheme
Discussions
Conclusions

3. Introduction (1/5) Why do we need the traveler’s check？
Some risks in abroad travel
Case 1
Freeze! Give me some money or costly goods.
Don’t kill me! I give you all my own money.
traveler
robber

4. Introduction (2/5) Case 2 Where is my wallet? Shopping shop Walk fast
traveler
traveler
traveler
wallet

5. Introduction (3/5) Malicious guys may forge people’s credit cards
I want to buy some goods.
OK!
Thank you.
Forgery credit card
Malicious man
Sales man
We need traveler’s check to mitigate possible risks

6. Introduction (4/5) Traditional traveler’s check
Deposit equivalent payment to bank
issuing checks
Need to sign the traveler’s check and
show their passport to the bank

7. Introduction (5/5) Two problems
Forging the traveler’s check or the passport
Impersonating the legal check holder

8. Proposed scheme (1/7)
Low computations
Mutual authentication

9. Proposed scheme (2/7) Registration Phase money Bank Traveler (User)
(The check center)
E-traveler’s check

10. Proposed scheme (3/7) Payment Phase E-traveler’s check Traveler (User)
communicate
Traveler (User)
Bank
(The check center)
Hotel
(The e-traveler’s check organization)
cash

11. Proposed scheme (4/7) Notations IDi：identity of user i
IDcc：identity of check center
IDeco：identity of e-traveler’s check organization
PWi：password of user i
MONi：total money in the e-traveler’s check
CASi：the cash that the user wants to cash the e-traveler’s check
K1：the shared key between user and check center
K2： the shared key between check center and e-traveler’s check organization
T：timestamp
EK：symmetric encryption with the secret key K

12. Proposed scheme (5/7) User bank Registration Phase Smart card
Secure channel

13. Proposed scheme (6/7)
Payment Phase
Database
User
hotel
bank

14. Proposed scheme (7/7)
Payment Phase
Database
hotel
bank
User

15. Discussions (1/2) Requirements:
The e-traveler’s check must have a unique identity
The e-traveler’s check can only be generated by the check-issuing bank or the authorized organization with the applicant
Only the legal check holder can have the e-traveler’s check cashed
The check-issuing bank, the check-cashing organization, and the e-traveler’s check holder can authenticate one another

16. The e-traveler check organization Chang and Chang’s scheme*
Discussions (2/2) Ui
The e-traveler check organization
(e.g. hotel)
The check center
(e.g. bank)
Chang and Chang’s scheme*
Our scheme
EPK( ) ：the public key encryption with PK
Π：the multi-multiplication operation
H( ) ：one-way hash function
EK( ) ：the symmetric encryption with secret key K
⊕：XOR
*: Chang, Y. F. and Chang, C. C., “E-traveler’s Checks with Reciprocal Authentication,” Journal
of Electronic Commerce Research, Vol. 5, No. 2, pp , 2004.

17. Conclusions
Simple and efficient
Mutual authentication