The Advanced of Fuzzy Vault Using Password - Advances in Computational Science and Engineering - page 40

Fig. 12. Blended Substitution Attack
6. Blended Substitution Attack[9]
In a substitution attack, a user enrolls his biometric data TU and a secret SU. In user
enrollment, an attacker injects another set of biometric data TA and another secret SA
in the user's template. The attacker's data may be directly injected before encoding.
Then database has only the attacker's data.
3.2 The Problem of K. Nandakumar's Scheme
Even if each vault is constructed with different polynomials and chaff points, if same
biometric data is reused for different vaults, security of the vault decreases. If an at-
tacker can obtain two vaults from same biometric data, he can easily identify hidden
minutiae points by correlating two vaults. This vulnerability allows cross-matching of
templates across different systems [9]. To solve this problem, K.Nandakumar pro-
posed a new scheme for hardening a fingerprint minutiae-based fuzzy vault using
password. However, if user's passwords are same in multiple enrollments, all finger-
prints of user are transformed by same password. In this case, because fingerprints
used in multiple enrollments have same password, an attacker can compute trans-
formed template in the vaults. This type of attack is called Attack via Record Multi-
plicity (ARM). If an attacker collects enrolled vaults in different systems which have
same implementation, then he can compute the transformed template by comparison
each vault [9].
If an attacker computes transformed template in ARM and obtain biometric tem-
plate of a genuine user, he can easily compute password of user.
3.3 The Attacks Scenario
1. Client enrolls transformed template by password T at different systems.
2. Each server of different systems generates vault using transformed template of
client and chaff points.
3. An attacker attempts ARM to database of each sever, then can obtain many vaults
V [9].
4. An attacker can collect transformed templates Q' of client by comparison each
vault.
5. An attacker can obtain a fingerprint impression Q of the genuine user without any
knowledge [9].
6. An attacker who has template Q and transformed template Q' of authorized client
can compute password T from (1): Q' u = (Q u + T u ) mod (2 Bu ), Q'v = (Q v + T v ) mod
(2 Bv ), Q' θ = (Q θ + T θ ) mod (2 Bθ ). Q' + N 2 B = Q + T. Q' + N 2 B - Q = T. B is length