Java Script Kiddie 2

Last updated 3 years ago

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Solution

Webpage source code:

 <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 = "00000000000000000000000000000000";
                 var shifter;
                 if(u_in.length == key.length){
                     key = u_in;
                 }
                 var result = [];
                 for(var i = 0; i < LEN; i++){
                     shifter = Number(key.slice((i*2),(i*2)+1));
                     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>

Run $.get("bytes", function(resp) {bytes = Array.from(resp.split(" "), x => Number(x));}); from the source code in developer console to get list of bytes:

 143 224 86 71 69 249 251 10 253 96 0 114 121 72 68 119 179 127 191 114 13 159 207 114 249 0 0 79 9 192 95 0 174 239 118 2 0 187 54 65 21 0 156 36 0 65 138 0 222 49 59 95 114 34 0 202 155 120 200 95 73 55 11 82 0 179 231 31 69 252 68 176 174 7 54 87 0 73 110 108 137 121 0 226 165 127 26 90 66 3 247 88 155 20 191 220 0 0 78 241 113 78 1 122 0 110 206 219 212 188 243 57 164 80 1 91 158 10 68 193 1 14 163 228 11 171 193 55 48 0 0 24 188 0 94 243 84 3 52 0 20 73 175 84 82 0 69 149 143 73 16 35 48 146 241 13 239 48 63 206 201 16 96 126 32 134 80 52 151 209 216 0 0 227 252 92 191 110 25 46 34 15 126 135 152 89 211 237 183 239 252 102 59 36 54 34 210 90 213 47 23 205 187 81 127 140 199 23 127 164 252 225 221 53 7 32 216 173 65 63 198 105 180 7 214 239 158 226 141 149 210 249 73 123 71 91 199 235 203 239 133 187 217 95 103 243 204 107 255 226 207 59 127 249 131 249 241 7 181 66 38 73 218 102 0 159 106 117 171 231 197 32 249 218 75 217 199 221 178 128 159 248 128 213 51 0 241 75 127 73 46 210 252 250 102 59 122 13 85 56 199 31 11 248 152 209 107 15 240 46 223 54 125 135 132 231 216 105 2 227 187 226 175 222 96 2 43 109 191 83 213 211 184 91 86 238 172 97 100 16 85 139 32 191 110 223 37 238 155 133 251 210 252 18 157 210 139 176 9 11 128 241 38 204 1 183 168 13 153 223 60 107 16 62 241 154 32 223 90 51 73 22 121 55 20 177 73 161 177 164 252 206 255 103 110 141 196 163 141 94 4 138 31 91 182 108 250 173 200 127 113 69 154 126 59 82 253 84 253 200 7 242 61 96 149 226 52 134 223 96 237 180 91 21 73 56 0 235 73 243 173 176 100 242 47 147 44 156 149 38 11 8 127 196 228 226 174 95 88 57 40 71 65 24 91 127 84 9 109 37 91 223 157 254 228 103 157 213 146 72 203 211 0 77 239 180 218 205 189 91 126 191 40 31 242 131 90 19 164 82 53 211 246 171 243 121 69 249 243 31 169 20 195 178 32 181 244 236 95 191 16 183 191 174 249 204 169 167 176 59 241 41 43 52 211 183 59 157 251 156 228 119 254 11 107 25 101 108 153 44 43 12 113 171 39 254 193 77 92 92 146 0 206 183 126 196 196 254 127 17 80 173 159 38 246 101 212 196 16 201 81 90 245 215 61 166 176 105 227 248 189 173 179 197 198 60 54 181 62 143 231 163 247 126 79 118 145 96 54 169 16 109 206 11 72 27 106 154 55 183 26 184 111 251 85 210 55 127 242 205 23 221 46 212 29 27 128 73 71 19 252 203 231 51 212 59 127 198 12 65 191 254 233 231 157 89 47 250 254 79 244 230 238 183 155 255 142 223 229 214 110 157 115 236 243 73 231 126 193 174 175 251 130 89 213 0 0 185

This website is similar to the first "Java Script Kiddie" except for this line: shifter = Number(key.slice((i*2),(i*2)+1));. This effectively ignores every second value in the key. Since var LEN = 16 is the same, the script for the previous challenge can be used again but with a random value (I chose 0) added between character.

Run . For each character of the key, this script will try all digits until one is found that places the expected value in the current location. It also adds padding (0) after each digit found.

Output:

 Key: 50706000107050006010009030000030
 Key Length: 32

Enter key into website and save image:

Use zbar (sudo apt install zbar-tools): zbarimg index.png and get the flag:

 QR-Code:picoCTF{b19be0d3b70ffc63b6367ecf136e853e}
 scanned 1 barcode symbols from 1 images in 0.03 seconds

Flag

picoCTF{b19be0d3b70ffc63b6367ecf136e853e}

Solution

Webpage source code:

 <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 = "00000000000000000000000000000000";
                 var shifter;
                 if(u_in.length == key.length){
                     key = u_in;
                 }
                 var result = [];
                 for(var i = 0; i < LEN; i++){
                     shifter = Number(key.slice((i*2),(i*2)+1));
                     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>

Run $.get("bytes", function(resp) {bytes = Array.from(resp.split(" "), x => Number(x));}); from the source code in developer console to get list of bytes:

 143 224 86 71 69 249 251 10 253 96 0 114 121 72 68 119 179 127 191 114 13 159 207 114 249 0 0 79 9 192 95 0 174 239 118 2 0 187 54 65 21 0 156 36 0 65 138 0 222 49 59 95 114 34 0 202 155 120 200 95 73 55 11 82 0 179 231 31 69 252 68 176 174 7 54 87 0 73 110 108 137 121 0 226 165 127 26 90 66 3 247 88 155 20 191 220 0 0 78 241 113 78 1 122 0 110 206 219 212 188 243 57 164 80 1 91 158 10 68 193 1 14 163 228 11 171 193 55 48 0 0 24 188 0 94 243 84 3 52 0 20 73 175 84 82 0 69 149 143 73 16 35 48 146 241 13 239 48 63 206 201 16 96 126 32 134 80 52 151 209 216 0 0 227 252 92 191 110 25 46 34 15 126 135 152 89 211 237 183 239 252 102 59 36 54 34 210 90 213 47 23 205 187 81 127 140 199 23 127 164 252 225 221 53 7 32 216 173 65 63 198 105 180 7 214 239 158 226 141 149 210 249 73 123 71 91 199 235 203 239 133 187 217 95 103 243 204 107 255 226 207 59 127 249 131 249 241 7 181 66 38 73 218 102 0 159 106 117 171 231 197 32 249 218 75 217 199 221 178 128 159 248 128 213 51 0 241 75 127 73 46 210 252 250 102 59 122 13 85 56 199 31 11 248 152 209 107 15 240 46 223 54 125 135 132 231 216 105 2 227 187 226 175 222 96 2 43 109 191 83 213 211 184 91 86 238 172 97 100 16 85 139 32 191 110 223 37 238 155 133 251 210 252 18 157 210 139 176 9 11 128 241 38 204 1 183 168 13 153 223 60 107 16 62 241 154 32 223 90 51 73 22 121 55 20 177 73 161 177 164 252 206 255 103 110 141 196 163 141 94 4 138 31 91 182 108 250 173 200 127 113 69 154 126 59 82 253 84 253 200 7 242 61 96 149 226 52 134 223 96 237 180 91 21 73 56 0 235 73 243 173 176 100 242 47 147 44 156 149 38 11 8 127 196 228 226 174 95 88 57 40 71 65 24 91 127 84 9 109 37 91 223 157 254 228 103 157 213 146 72 203 211 0 77 239 180 218 205 189 91 126 191 40 31 242 131 90 19 164 82 53 211 246 171 243 121 69 249 243 31 169 20 195 178 32 181 244 236 95 191 16 183 191 174 249 204 169 167 176 59 241 41 43 52 211 183 59 157 251 156 228 119 254 11 107 25 101 108 153 44 43 12 113 171 39 254 193 77 92 92 146 0 206 183 126 196 196 254 127 17 80 173 159 38 246 101 212 196 16 201 81 90 245 215 61 166 176 105 227 248 189 173 179 197 198 60 54 181 62 143 231 163 247 126 79 118 145 96 54 169 16 109 206 11 72 27 106 154 55 183 26 184 111 251 85 210 55 127 242 205 23 221 46 212 29 27 128 73 71 19 252 203 231 51 212 59 127 198 12 65 191 254 233 231 157 89 47 250 254 79 244 230 238 183 155 255 142 223 229 214 110 157 115 236 243 73 231 126 193 174 175 251 130 89 213 0 0 185

Run . For each character of the key, this script will try all digits until one is found that places the expected value in the current location. It also adds padding (0) after each digit found.

Output:

 Key: 50706000107050006010009030000030
 Key Length: 32

Enter key into website and save image:

Use zbar (sudo apt install zbar-tools): zbarimg index.png and get the flag:

 QR-Code:picoCTF{b19be0d3b70ffc63b6367ecf136e853e}
 scanned 1 barcode symbols from 1 images in 0.03 seconds

Flag

picoCTF{b19be0d3b70ffc63b6367ecf136e853e}

Java Script Kiddie 2

Java Script Kiddie 2

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