create a single function in matlab that can both encrypt and decrypt a message u

Question

create a single function in matlab that can both encrypt and decrypt a message using an auto-key cipher

1. Remove any special characters, punctuation and spaces from the message to be encoded.

2. Convert all lowercase letters to uppercase and use the 26-character alphabet used to create the encryption squares.

3. Generate the encryption/decryption key.

4. Encrypt/decrypt the message and output the result.

. 5. Decrypt the given message.

cannot use find function

must use loops and branching statements

Explanation / Answer

Encrypt

function cText = encrypt(pText, key)
    v = vigenere;
    exclude = regexp(pText, '[^a-zA-Z ]');
    pText(exclude) = [];
    key = lower(key) - double('a') + 1;
    key(key < 0) = 27;
    pText = lower(pText) - double('a') + 1;
    pText(pText < 0) = 27;
    keyIndex = mod(0:(numel(pText)-1), numel(key))+1;
    k = key(keyIndex);
    cText = arrayfun(@(m,n) v(m,n), k, pText) - 1;
    cText(cText == 26) = double(' ') - double('a');
    cText = upper(char(cText + double('a')));

decrypt

function pText = decrypt(cText, key)
    v = vigenere;
    key = lower(key) - double('a') + 1;
    key(key < 0) = 27;
    cText = lower(cText) - double('a') + 1;
    cText(cText < 0) = 27;
    keyIndex = mod(0:(numel(cText)-1), numel(key))+1;
    k = key(keyIndex);
    pText = arrayfun(@(m,n) find(v(m,:) == n), k, cText) - 1;
    pText(pText == 26) = double(' ') - double('a');
    pText = upper(char(pText + double('a')));

vigenere

function v = vigenere
    count = 27;
    alpha = 1:count;
    v = arrayfun(@(n) circshift(alpha, [0, -n]), 0:count-1, ...
                 'UniformOutput', false);
    v = reshape([v{:}], count, count);

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