Electoral processes using electronic devices allow voters to cast electronically. Devices such as personal computers, Direct Record Machines (DRE) voting machines, and smartcards, among others, in conjunction with private nets or the Internet have been the main tools to implement electronic voting systems (e-voting). Some years ago, mobile devices had not been considered due to their storage restrictions and low computational power; however, nowadays the technology in these devices has advanced and it is possible to implement complicated applications that offer security services such as confidentiality and authentication. In this paper, a reliable and efficient e-voting system for Android Smartphone is implemented. The e-voting proposed herein is composed of three entities: the authentication server (AS), the voting server (VS) and the voter (V) which runs on an Android Smartphone. Two short messages, between V and AS, are necessary to generate an electronic ballot. In order to cast a vote, one more message containing the ballot is sent from V to VS. Bilinear pairing functions are used to verify the signatures contained in the electronic ballot. Each ballot has short lengths, implying improvements in transmission times. Additionally, considering that the most costly operations such as bilinear pairing are not performed in V, the results obtained in tests show that the e-voting system is efficient.