Caesar cipher: Difference between revisions

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</syntaxhighlight>

=={{header|SparForte}}==

As a structured script.

<syntaxhighlight lang="ada">#!/usr/local/bin/spar

pragma annotate( summary, "caesar" )

@( description, "Implement a Caesar cipher, both encoding and ")

@( description, "decoding. The key is an integer from 1 to " )

@( description, "25. This cipher rotates (either towards left ")

@( description, "or right) the letters of the alphabet (A to " )

@( description, "Z). " )

@( see_also, "http://rosettacode.org/wiki/Caesar_cipher" )

@( author, "Ken O. Burtch" );

pragma license( unrestricted );

pragma restriction( no_external_commands );

procedure caesar is

type cipher_value is new natural;

function to_cipher_value(c: character; offset: character) return cipher_value is

cv : integer;

begin

cv := ( numerics.pos(c)-numerics.pos(offset) ) mod 26;

return cipher_value(cv);

end to_cipher_value;

function to_character(cv: cipher_value; offset: character) return character is

begin

return strings.val( integer(cv) + numerics.pos(offset) );

end to_character;

function encrypt( plain: string; key: cipher_value) return string is

cv : cipher_value;

cipher_char : character;

cipher_text : string;

plain_char : character;

begin

for i in 1..strings.length( plain ) loop

plain_char := strings.element( plain, i);

if plain_char >= 'A' and plain_char <= 'Z' then

cv := ( to_cipher_value( plain_char, 'A')+key ) mod 26;

cipher_char := to_character( cv, 'A' );

elsif plain_char >= 'a' and plain_char <= 'z' then

cv := ( to_cipher_value( plain_char, 'a')+key ) mod 26;

cipher_char := to_character( cv, 'a' );

else

cipher_char := plain_char;

end if;

cipher_text := strings.overwrite( @, i, string( cipher_char ) );

end loop;

return cipher_text;

end encrypt;

text: string := get_line;

key: constant cipher_value := 3; -- Default key from "Commentarii de Bello Gallico"

begin

put_line("Plaintext ------------>" & text);

text := encrypt(text, key);

put_line("Ciphertext ----------->" & text);

text := encrypt(text, -key);

put_line("Decrypted Ciphertext ->" & text);

end caesar;</syntaxhighlight>

=={{header|SSEM}}==

ASCII didn't exit in 1948, and the task specification explicitly says we only need to convert Roman capitals; so we adopt a simpler encoding, representing the letters of the alphabet from <tt>A</tt>=0 to <tt>Z</tt>=25.