A DPA Countermeasure by Randomized Frobenius Decomposition Tae-Jun Park, Mun-Kyu Lee*, Dowon Hong and Kyoil Chung * Inha University
WISA Outline Side channel analysis Side channel analysis I Frobenius expansion Frobenius expansion II Random decomposition Random decomposition III Conclusion Conclusion IV
WISA Power Analysis Kocher, Crypto 99 Powerful technique to recover the secret information by monitoring power signal Two kinds of power analysis - SPA : Simple power analysis - DPA : Differential power analysis
WISA Power Analysis on Elliptic Curve Coron, CHES 99 Naïve implementation of ECC are highly vulnerable to SPA and DPA Various methods have been proposed - Hasan suggested several countermeasures on Koblitz curves, 2001, IEEE Transactions on computers - Ciet et al. proposed randomizing the GLV decomposition to prevent DPA in GLV curves CHES 2002
WISA The Goal of This Talk New Countermeasure against DPA on ECC Applied to any curve where Frobenius method can be used Two dimensional generalization of Coron’s method 15.3 ~34.0% extra computations
WISA Elliptic Curve Let be the prime power is of or Otherwise x y - To avoid the MOV attack Use only nonsupersingular elliptic curve
WISA Frobenius Endomorphism The Frobenius endomorphisms of The minimal polynomial of the Frobenius endomorphism
WISA Frobenius Expansion-(1) The endomorphism ring of nonsupersingular elliptic curve is the order in the imaginary quadratic field The ring is a subring of the endomorphism ring Mueller proposed a Frobenius expansion method by iterating divisions - fast scalar multiplication on elliptic curves over small fields of characteristic two - Division by the Frobenius endomorphism in the ring
WISA Division by in the looks like division by complex number in the Gaussian integer Lemma: Suppose that be even (resp., odd) prime power. Let. There exists an integer and an element s.t. Frobenius Expansion-(2)
WISA Frobenius Expansion-(3) By iterating the process of divisions by with remainder, one can expand with
WISA Division by in -(1)
WISA Let be the lattice generated by 1 and : is isomorphic to All elements in which can be divided by for example, all numbers divided by 2 is of the form The set of such elements is generated by and : Division by in -(2)
WISA Divide by with remainder - If, then there exist s. t. - If not, move horizontally left or right to for suitable Division by in -(3)
WISA Random Decomposition-(1) Transform to random lattice - Choose random integer where
WISA Random Decomposition-(2)
WISA Random Decomposition-(3)
WISA Random Decomposition-(4) Lemma : For any, we can find s. t. with the Euclidean length of is bounded by
WISA Random Decomposition-(5)
WISA Scalar Multiplication Scalar multiplication - is expanded as - By Mueller’s expansion method - A scalar multiplication
WISA Overhead
WISA Conclusion Our method can be applied to all kind of elliptic curves It can be used in conjunction with other countermeasure It will be generalized to hyperelliptic curves