“…For this reason, nowadays a great number of different applications require the use of e-signature and non-repudiation services such as (mobile) electronic payment systems (Hassinen and Hyppönen Haataja, 2006), certified e-mail (Asokan Schunter, 2009), contract signing protocols (Asokan Schunter, 2009;Chadha et al, 2005;RuizMartínez et al, 2009), e-auctions (Lee et al, 2009), long-term preservation of documents (Blaič et al, 2007), e-procurement (Liao et al, 2002), e-invoices (Kaliontzoglou et al, 2006), etc. The purpose of the e-signature is to guarantee the authenticity and integrity of electronic documents in a way equivalent to the handwritten signature in paper documents (Rossnagel, 2004;Ruiz-Martínez et al, 2007).…”