1. A computer-implemented method comprising: a) obtaining, by a computer system including one or more processors, a multi-touch input sequence including 1) determining, at a plurality of time instances, a mapping from an unordered set of at least four touch points to an ordered set of at least four fingertips, wherein for at least one of the plurality of time instances, the mapping from the unordered set of at least four touch points to the ordered set of at least four fingertips is subject to a constraint that the ordered set of at least four touch points defines a simple polygon; and b) controlling, by the computer system, access to a device, service, or information, using the obtained multi-touch input sequence.