1. Authenticated QKD protocol using one-time ID
GSIS / CIST
Hwa Yean Lee

2. Contents Introduction Authentication with one-time ID
Quantum Key distribution
Security proof
Conclusion

3. 1. Introduction QKD (Quantum Key Distribution) protocols Advantage
: Unconditional security
Disadvantage
: Vulnerability to the Man-in-the middle attack

4. 1. Introduction(2)
Miloslav Dusek, Ondrej Haderka, Martin Hendrych, and Robert Myska, PRA, 60, (1999)
Bao-Sen Shi, Jian Li, Jin-Ming Liu, Xiao-Feng Fan, Guang-Can Guo, Physics Letters A 281  (2001)
Guihua Zeng and Weiping Zhan, PRA, 61, (2000)
Daniel Ljunggren, Mohamed Bourennane, and Anders Karlsson, PRA, 62, (2000)
Takashi Mihara, PRA, 65, (2002)

5. 2. Authentication with one-time ID
Preparation
Each user register him to the arbitrator
: secret user and one-way function
One-way authentication key of a user, Alice is
where is a count.
If is 1, then the Hadamard operator is applied, else the identity operator is applied to the ith qubit.
If does not have enough length to encode the qubits, then can be used, where

6. 2. Authentication with one-time ID (2)
Procedure of the authentication
Alice request a secure communication with Bob to the arbitrator.
The arbitrator prepares GHZ tripartite states.
He encodes Alice’s and Bob’s particles of GHZ states with and , respectively.
where is Alice’s authentication key
and is Bob’s.

7. 2. Authentication with one-time ID (3)
Procedure of the authentication(2)
The arbitrator sends the encoded qubits to Alice and Bob respectively.
Alice and Bob decode their qubits with their authentication key and selects some bits.
Alice and Bob measure the bits and compare the results.
If the results are same, they can authenticate each other and do the following key distribution procedure. Otherwise they abort the protocol.

8. 2. Authentication with one-time ID (4)
Transformation of the GHZ states

9. 3. Quantum Key distribution
Procedure of the key distribution
Using the remaining particles after authentication, Alice and Bob randomly make an operation either or on each particles, respectively.
Alice sends her particles to the arbitrator and Bob sends his to Alice.
The arbitrator perform C-NOT operation, where the control qubit is his and the target qubits is from Alice.
The arbitrator measures each qubits(Alice’s and his) and announces the measurement outcomes are same(O) or not(X).

10. 3. Quantum Key distribution (2)
Procedure of the key distribution (2)
Alice measures the GHZ particles received from Bob.
Using the information published by the arbitrator, Alice can find Bob’s sequence of the operations.
The Bob’s sequence of the operations can be used as a raw secret key.

11. 3. Quantum Key distribution (3)
Operation
Transformation of GHZ states
C-NOT operation
Opened
info.
MO of Bob’s qubit
Alice
Bob O X 1

12. 4. Security proof Man-in-the middle attack
In the authentication process
Eve introduces errors
with probability ¼
for each check bit
in the authentication
procedure.
On knowing
the hash function,
Eve can estimate only
some bits of hashed value.
The Arbitrator
Alice
Bob
Eve

13. 4. Security proof (2) Intercept-resend attack
Intercepts both the qubits heading to Alice or Bob in the authentication and the qubits heading to Alice or the authentication in the key distribution.
When Eve intercepts one-side in the key distribution,
the probability of detection is 3/8.
When Eve intercepts both-side in the key distribution,
the probability of detection is 7/16.
But she cannot be aware of the exact key since Alice and Bob’s information of operations are not exposed to Eve.

14. 4. Security proof (3) Intercept-resend attack (2)
Intercept only the qubits transmitted in the key distribution
Eve only can know Alice and Bob use same operation or not.
The probability of inferring correct key is

15. Transmitted GHZ states
4. Security proof (4)
Eve Eavesdrops Alice’s (Bob’s) qubits transmitted to the arbitrator (Alice) after Alice and Bob make operations on decoded GHZ states
Operation
Transmitted GHZ states
Eve’ MO
Changed state
CNOT op.
Opend info
Alice
Bob
0(0)
1(1) O X
0(1)
1(0)

16. 5. Conclusion QKD with authentication using one-time ID is proposed.
Authentication with one-time ID can be used on the various fields of quantum cryptography.
The neutrality of the arbitrator is important for the security of the proposed scheme.
 More research on this problem are needed.