Vigenère cipher: Difference between revisions

=={{header|Liberty BASIC}}==

<lang lb>

ori$ = "Beware the Jabberwock, my son! The jaws that bite, the claws that catch!"

key$ = filter$("vigenerecipher")

print ori$

print key$

enc$ = encrypt$(ori$, key$)

print enc$

dec$ = decrypt$(enc$, key$)

print dec$

end

function encrypt$(text$, key$)

flt$ = filter$(text$)

encrypt$ = ""

j = 1

for i = 1 to len(flt$)

m$ = mid$(flt$, i, 1)

m = asc(m$)-asc("A")

k$ = mid$(key$, j, 1)

k = asc(k$)-asc("A")

j = (j mod len(key$)) + 1

c = (m + k) mod 26

c$=chr$(asc("A")+c)

encrypt$=encrypt$+c$

next

end function

function decrypt$(flt$, key$)

decrypt$ = ""

j = 1

for i = 1 to len(flt$)

m$ = mid$(flt$, i, 1)

m = asc(m$)-asc("A")

k$ = mid$(key$, j, 1)

k = asc(k$)-asc("A")

j = (j mod len(key$)) + 1

c = (m - k + 26) mod 26

c$=chr$(asc("A")+c)

decrypt$=decrypt$+c$

next

end function

function filter$(ori$)

'a..z A..Z go caps, other skipped

filter$=""

for i = 1 to len(ori$)

c$ = upper$(mid$(ori$,i,1))

if instr("ABCDEFGHIJKLMNOPQRSTUVWXYZ", c$) then filter$ = filter$ + c$

next

end function

</lang>

Beware the Jabberwock, my son! The jaws that bite, the claws that catch!

VIGENERECIPHER

WMCEEIKLGRPIFVMEUGXQPWQVIOIAVEYXUEKFKBTALVXTGAFXYEVKPAGY

BEWARETHEJABBERWOCKMYSONTHEJAWSTHATBITETHECLAWSTHATCATCH