{{
  variable offset
  : rotate  ( cb-c ) tuck - @offset + 26 mod + ;
  : rotate? (  c-c )
    dup 'a 'z within [ 'a rotate ] ifTrue
    dup 'A 'Z within [ 'A rotate ] ifTrue ;
---reveal---
  : ceaser  (  $n-$ )
    !offset dup [ [ @ rotate? ] sip ! ] ^types'STRING each@ ;
}}

( Example )
"THEYBROKEOURCIPHEREVERYONECANREADTHIS" 3 ceaser   ( returns encrypted string )
23 ceaser   ( returns decrypted string )