Three Factor Scheme for
Biometric-Based
Cryptographic Key
Regeneration Using Iris
Sanjay KANADE, Danielle CAMARA, Emine KRICHEN,
Dijana PETROVSKA-DELACRÉTAZ, and Bernadette DORIZZI
TELECOM & Management SudParis
Evry, France
Last Updated 17th September, 2008
This work was funded by the
Outline
• Why Combine Biometrics with Cryptography
• State of the art
• Existing works based on iris
• Iris Code Matching as Error Correction Problem
• Iris Code Shuffling
• Increasing Error Correction Capability of Hadamard
Code
• Experimental Results
• Security Analysis
Why Combine Biometrics with
Cryptography
• Shortcomings of Biometrics:
– Biometric data is noisy
– Lack of revocability: - Biometric templates once
stolen/compromised cannot be replaced and new
template cannot be issued
– No template diversity
• Shortcomings of Cryptography:
– Easy to guess and can be stolen
– No strong link between authenticator & user
identity
State of the Art
Three main categories:
• Protecting biometrics and adding revocability
to biometrics – e.g. cancelable biometrics,
etc.
• Cryptographic key generation from biometrics
– e.g. Hardened password, Fuzzy extractors,
etc.
• Cryptographic key regeneration using
biometrics – e.g. fuzzy vault, fuzzy
Existing Works on
Key Regeneration Using Iris
• Hao et al. scheme
– Uses Reed-Solomon and Hadamard codes for correcting
errors in iris codes
– 25% error correction is possible
– Cannot change error correction capability of Hadamard
codes
– For comparatively noisy databases (like ICE), this scheme
cannot work because many genuine comparisons have
Hamming distance greater than 25%
• Bringer et al. scheme
– Reed-Muller and Product codes are used
Iris Code Matching as Error
Correction Problem
Noisy
Communication Channel
Data Encoder
Data Decoder
K
K’
Noise causing elements
Iris Code 1
Iris Code 2
• Variations in iris codes are treated as errors and are corrected by the
decoder.
• Error correcting capacity of the decoder should be such that it can
separate genuine users from impostors
Schematic Diagram of the Key
Regeneration Scheme
Iris Code Shuffling
• A shuffling key is generated using a password
• Iris code is divided into blocks;
number of blocks = number of bits in shuffling key
• If a bit in the key is 1, corresponding iris code block
is moved to the beginning; otherwise it is moved to
the end
• This scheme increases Hamming distance for
impostors, but for genuine users Hamming distance
is unchanged
Iris Code Shuffling – Schematic
Diagram
Hamming Distance Distributions –
Before and After Shuffling
Overlap between genuine and impostor users’ Hamming
distance is decreased because of shuffling
Error Correcting Codes
• Iris codes have two types of errors:
– Background errors:- Due to camera noise, iris
distortion, image-capture effects, etc. These are
uniformly distributed
– Burst errors:- Due to eye-lids, eye-lashes, and
specular reflections. These occur as bursts.
• We use
Hadamard code
to correct
background errors and
Reed-Solomon Codes
Increasing Error Correction
Capability of Hadamard Code
• Hadamard code’s inherent error correction capacity is 25%
which cannot be changed. Large number of genuine users
comparisons where the hamming distance is more 25%.
• Adding similarity to the data can change the error distribution
by decreasing the number of errors in a block
– Let there be p errors in n bits
– Adding q zeros uniformly to n will change the error ratio to
R=p/(q+n); if R < 25%, p errors can be corrected
– Thus by changing q we can change (increase) the error
correction capacity of Hadamard code
Database Used for System
Evaluation
• NIST-ICE Database
– Exp-1 - 1,425 images of right irises of 124 users
• 12,214 genuine and 1,002,386 impostor comparisons
– Exp-2 - 1,528 images of left irises of 120 users
Experimental Results
• Experimental parameters
• m = 6, Number of bits in each Reed-Solomon code block
• n
s= 61, Number of blocks after Reed-Solomon encoding
• 8 zeros added to every 12 bits in the iris code; modified iris code
length = 1,980, which is truncated to 1,952 bits.
• t
sError correction capability of Reed-Solomon Code
• t
sacts as threshold by adjusting which we can fine tune the
t
sKey
Length
ICE-Exp-1
ICE-Exp-2
FAR
FRR
FAR
FRR
11
234
0.0008
2.48
0.003
3.49
14
198
0.055
1.04
0.124
1.41
15
186
0.096
0.76
0.21
1.09
Security Analysis
22
Entropy log
NH
N
w
=
⎛ ⎞
⎜ ⎟
⎝ ⎠
N is the number of degrees of freedom which can be calculated as
where p = mean of the binomial distribution, and
σ = standard deviation of the distribution
w = number of bits corresponding to the error correction capacity (which is 35%)
2
(1
) /
N
=
p
−
p
σ
In our experiments, N = 1,172,
w = 410 corresponding to 35% error correction capacity, thus
Comparison With Other Iris
Based Systems
• RSH – Reed-Solomon and Hadamard codes
• RMP – Reed-Muller and Product codes
[1] J. Bringer, H. Chabanne, G. Cohen, B. Kindarji, and G. Zémor, "Optimal iris fuzzy sketches," in IEEE
Conference on Biometrics: Theory, Applications and Systems, 2007.
[2] F. Hao, R. Anderson, and J. Daugman, "Combining crypto with biometrics effectively," IEEE Transactions
on Computers, vol. 55, no. 9, pp. 1081-1088, 2006.
Authors
ECC
Key Bits FRR in %
FAR in %
Entropy
in bits
Database
Hao et al.[2]
RSH
140
0.47
0
44
proprietary
Bringer et al.[1]
RMP
42
5.62
10
-5-
ICE
-
RSH
186
0.76
0.096
83
ICE-Exp-1
-
RSH
234
2.48
0.0008
83
ICE-Exp-1
Conclusions and Discussions
•
Shuffling makes the iris codes more random, which helps in increasing the entropy; also it
acts as interleaver and helps in error correction by distributing the error bursts
•
The zero insertion scheme increases the error correction capability of Hadamard code which
is otherwise fixed
•
Longer keys compared to other schemes can be obtained with the proposed scheme which
will have nearly 83 bit entropy
•
The keys obtained with this scheme can be used in cryptographic systems; otherwise Hash
values of the original and regenerated keys can be compared to securely verify the user
•
The locked iris template does not reveal any biometric information thereby protecting the
biometric data
•
In case of compromise detection, the cryptographic key, smart card, and password can be
changed and a new template can be issued; thus the templates are revocable
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