Jorge L. Hernandez-Ardieta Ana Isabel González-Tablas Ferreres Benjamín Ramos Arturo Ribagorda Extended electronic signature policies. 268-277 2009 SIN http://doi.acm.org/10.1145/1626195.1626261 conf/sin/2009 db/conf/sin/sin2009.html#Hernandez-ArdietaFRR09