Matlab - encriptar, decriptar, please help

. i need to take a='HIDETHEGOLDINTHETREXESTUMP'
AND MAKE it HI DE TH GO LD IN TH ET TR EX ES TU MP , PLEASE ADVISE... after that i need some help taking these digraphs and making loops for the following using this 5x5 key table as a reference

PLAYF
IREXM
BCDGH
JKNOS
TUVWZ

-if the letters appear on the same row of your table, replace them with the letters to their immediate right respectively (wrapping around to the left side of the row if a letter in the original pair was on the right side of the row.

-if the letters appear on the same column of your table,replace them with the leters immediately below respectively (wrapping around the top side of the column if a letter in the original pair was on the bottom side of the column)

-if the letters are not on the same row or column, replace them with the letters on the same row respectively but at the other pair of corners or the rectangle defined by the original pair. the incrypted letters lie on the same rows as the plaintext letters.=if both letters are the same(or only one letter is left), add an "X" after the first letter