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PicoCTF 2019 - Java Script Kiddie - Points: 400
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| <html> | |
| <head> | |
| <script src="jquery-3.3.1.min.js"></script> | |
| <script> | |
| var bytes = []; | |
| $.get("bytes", function(resp) { | |
| bytes = Array.from(resp.split(" "), x => Number(x)); | |
| }); | |
| function assemble_png(u_in){ | |
| var LEN = 16; | |
| var key = "0000000000000000"; | |
| var shifter; | |
| if(u_in.length == LEN){ | |
| key = u_in; | |
| } | |
| var result = []; | |
| for(var i = 0; i < LEN; i++){ | |
| shifter = key.charCodeAt(i) - 48; | |
| for(var j = 0; j < (bytes.length / LEN); j ++){ | |
| result[(j * LEN) + i] = bytes[(((j + shifter) * LEN) % bytes.length) + i] | |
| } | |
| } | |
| while(result[result.length-1] == 0){ | |
| result = result.slice(0,result.length-1); | |
| } | |
| document.getElementById("Area").src = "data:image/png;base64," + btoa(String.fromCharCode.apply(null, new Uint8Array(result))); | |
| return false; | |
| } | |
| </script> | |
| </head> | |
| <body> | |
| <center> | |
| <form action="#" onsubmit="assemble_png(document.getElementById('user_in').value)"> | |
| <input type="text" id="user_in"> | |
| <input type="submit" value="Submit"> | |
| </form> | |
| <img id="Area" src=""/> | |
| </center> | |
| </body> | |
| </html> |
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