ticated, a user must present the same biometric data
(more precisely a similar biometric data) and the same
random number. Howeverthis random number is gen-
erally not considered as secret, in the sense that it is
generally stored with the transformed template for the
verification step. Cancelable biometric systems must
meet the following four criteria, (Maltoni et al., 2003;
Jain et al., 2008; Nagar et al., 2010):
• Performance
The template transformation should not signifi-
cantly decrease the technical performance of the
original biometric system (accuracy).
• Revocability
It should be possible to revoke a biometric tem-
plate in case of compromission, and to generate a
new one from the original data.
• Irreversibility
From the transformed data, it should not be possi-
ble to obtain enough information about the origi-
nal biometric data.
• Unlinkability
It should be possible to generate different trans-
formed data for multiple applications, and no in-
formation should be deduced from the compari-
son or the correlation of different realizations.
The advantage of cancelable biometrics lies in the
ease of revoking the transformed template, by sim-
ply changing the associated random number. An-
other interest lies in the possibility to generate dif-
ferent templates to authenticate oneself to different
services from the same biometric raw data, with dis-
tinct random numbers (one for each service). Thus,
the random number should only be used for diver-
sification and revocability purposes and not for the
security, without a secure storage. More precisely,
the security of any cancelable biometric process re-
quires the associated transformation to be non invert-
ible: it means that it should be hard for an intruder
to recover the original raw biometric vector from the
transformed template and the random number. No-
tice that with this commonly admitted definition of
the non-invertibility property, the possibility to ap-
proximate the original biometric feature vector, given
the transformed template and the associated random
number, is not considered. Nevertheless, the recon-
struction of such sufficiently similar biometric tem-
plates, called preimage attack, is a major flaw for
cancelable biometric schemes, because in this case,
the authentication system could be spoofed. Different
definition for irreversibility are detailed in (Simoens
et al., 2012) with several criteria: full-leakage ir-
reversibility, authorized-leakage irreversibility and
pseudo-authorized leakage irreversibility. For exam-
ple, it is possible to generate an eligible fingerprint
given minutiae (Cappelli et al., 2007).
The BioHashing algorithm is one of the most pop-
ular cancelable biometric scheme, proposed for face
biometrics in (Goh and Ngo, 2003) and later for fin-
gerprints in (Teoh et al., 2004), which will be detailed
hereafter. The invertibility of the Biohashing algo-
rithm has been firstly investigated in (Cheung et al.,
2005; Lee et al., 2009). Recently, Nagar et al. pre-
sented a method based on optimization problems, to
recover a close approximation of face images, gener-
ated by the Biohashing algorithm (Nagar et al., 2010).
The main contribution of this paper is to analyze
this vulnerability of cancelable biometrics. We pro-
pose a new method to generate a biometric feature
vector approximating the original biometric feature,
based on genetic algorithms. Experiments are carried
out on fingerprint modality, with the BioHashing al-
gorithm, using the FVC2002 benchmark.
This paper is organized as follows. Section 2 pro-
vides a presentation of cancelable biometric schemes,
with a description of the BioHashing algorithm. Sec-
tion 3 then introduces genetic algorithms and their
application to template approximation. Finally, Sec-
tion 4 proposes experimental results on the FVC2002
database with the BioHashing algorithm.
2 BIOMETRIC DATA
PROTECTION
Biometric systems are used for identification or au-
thentication purpose. Identification process generally
involves a large database of biometric templates and
the verification phase consists in recovering the cor-
responding template in the database. The centralized
storage of non-protected biometric data is a major
threat for user privacy. Biometric authentication does
not necessarily use a centralized database and many
applications require an additional secure element as a
smart card for biometric data storage. However, the
centralized storage of protected biometric data is a
possible alternative, if this centralized approach is not
a privacy nor a security threat for the system.
2.1 Biometric Cryptosystems
Biometric cryptosystems associate a secret key with a
biometric template in order to protect the latter. It
includes fuzzy commitment, (Juels and Wattenberg,
1999) and fuzzy vaults, (Juels and Sudan, 2002).
Fuzzy commitments are based on error correcting
codes and do not require the storage of the biomet-
ric template. They have numerous applications on
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