chill-bundles/Resources/public/module/async_upload/downloader.js

var algo = 'AES-CBC';

var initializeButtons = (root) => {
    var
        buttons = root.querySelectorAll('a[data-download-button]');
    
    for (let i = 0; i < buttons.length; i ++) {
        initialize(buttons[i]);
    }
};

var initialize = (button) => {
    button.addEventListener('click', onClick);
};

var onClick = e => download(e.target);

var download = (button) => {
    console.log(button.dataset.key);
    var
        keyData = JSON.parse(button.dataset.key),
        //keyData, // = JSON.parse(keyString),
        ivData = JSON.parse(button.dataset.iv),
        iv = new Uint8Array(ivData),
        url = button.dataset.tempUrlGet,
        data, key
        ;
    console.log('keyData', keyData);
    console.log('iv', iv);
    console.log('url', url);
    
    window.crypto.subtle.importKey('jwk', keyData, { name: algo, iv: iv}, false, ['decrypt'])
            .then(nKey => {
                key = nKey;
                console.log(key);
        
                return window.fetch(url);
            })
            .then(r => {
                if (r.ok) {
                    return r.arrayBuffer();
                } else {
                    console.log(r);
                    throw new Error(r.statusCode);
                }
            })
            .then(buffer => {
                return window.crypto.subtle.decrypt({ name: algo, iv: iv }, key, buffer);
            })
            .then(decrypted => {
                var 
                    blob = new Blob([decrypted]),
                    url = window.URL.createObjectURL(blob)
                    ;
                button.href = url;
                button.removeEventListener('click', onClick);
            })
            .catch(error => {
                console.log(error);
            })
            ;
};

window.addEventListener('load', function(e) {
    console.log('load');
    initializeButtons(e.target);
});