**Majd Abazid, Nesma Houmani \* and Sonia Garcia-Salicetti**

SAMOVAR, Telecom SudParis, Institut Polytechnique de Paris, 9 rue Charles Fourier, 91011 Evry, France; majd.abazid@telecom-sudparis.eu (M.A.); sonia.garcia@telecom-sudparis.eu (S.G.-S.)

**\*** Correspondence: nesma.houmani@telecom-sudparis.eu

Received: 6 January 2020; Accepted: 4 February 2020; Published: 10 February 2020

**Abstract:** We aim at enhancing personal identity security on mobile touch-screen sensors by augmenting handwritten signatures with specific additional information at the enrollment phase. Our former works on several available and private data sets acquired on different sensors demonstrated that there are different categories of signatures that emerge automatically with clustering techniques, based on an entropy-based data quality measure. The behavior of such categories is totally different when confronted to automatic verification systems in terms of vulnerability to attacks. In this paper, we propose a novel and original strategy to reinforce identity security by enhancing signature resistance to attacks, assessed per signature category, both in terms of data quality and verification performance. This strategy operates upstream from the verification system, at the sensor level, by enriching the information content of signatures with personal handwritten inputs of different types. We study this strategy on different signature types of 74 users, acquired in uncontrolled mobile conditions on a largely deployed mobile touch-screen sensor. Our analysis per writer category revealed that adding alphanumeric (date) and handwriting (place) information to the usual signature is the most powerful augmented signature type in terms of verification performance. The relative improvement for all user categories is of at least 93% compared to the usual signature.

**Keywords:** automatic signature verification; touch-screen sensor; data quality; enrollment phase; performance assessment; augmented signature; security enhancement; mobile conditions
