algorithm - Electronic signature -

i asked code electronic signature form. can't understand thing description. qualification or missing?

here description:

mac008(x1, x2, …, xn) := rsa(sha-1(p(x1)||x1||p(x2)||x2||…||p(xn)||xn),d,n)   where:  || - symbol lines connecting x1, x2, …, xn inquiry parameters; p function returns parameter length. result provided three-segment number (e.g. 007) d – rsa secret exponent n- rsa module 

let's p1 defined returning "hello \x1, how you"

p1(chris) = "hello chris, how you".   

what asking turn

mac008(chris) = rsa(sha-1(hello chris, how youchris),somesecret,somersamodule) 

into modules "signature". sha-1 hashing algorithm turns set of data pre determined length string, or hash. rsa signature algorithm uses public/private key encryption scheme. freely make available public key, , encrypt hash private key. provides no data security, individual public key can positive data you, because way public key work on data set.