Methods for authentication or validation of the location of a putative source (ps) of a message, using time varying location determination (LD) signals that are received from J sources (J>1) of LD signals G(t;j;ps) that are spaced apart from the putative source. The putative source forms an augmented data signal that includes the original message, one or more segments g�t.sub.k(m),t.sub.k(m+1) ; j; ps!={G(t.sub.r ;j;ps).vertline.t.sub.k(m) .ltoreq.t.sub.r .ltoreq.t.sub.k(m+1) } of the LD signals for a selected time interval, a putative source asserted location L(t".sub.k(m) ;ps) for a time t".sub.k(m) in the selected time interval, and other identifying parameters. The augmented data signal is received by a central station that analyzes the LD signal segments and determines whether the asserted location L(t".sub.k(m) ;ps) is likely to be the true message source location. Part or all of the augmented data signal can be encrypted for transmission. One application is validation of use of licensed software on a computer whose location may be mobile. Another application is validation of votes cast from a plurality of remote voting sites.