feat: add crack api

lib/index.js

@@ -1,7 +1,86 @@
-exports.crack = function (iv, cipher, challenge) {
-  // TODO
+const log = require('log-update')
+const pad = require('left-pad')
+const ALL_HEX = Array.from(Array(256)).map((v, i) => pad(i.toString(16), 2, 0))
+// <- ['00', '01', ... 'fe', 'ff']
+
+function replace (buf, position, replacement) {
+  let end = position + replacement.length
+  if (position < 0) {
+    return replace(buf, buf.length + position, replacement)
+  }
+  if (end > buf.length) {
+    throw new Error('The replacement will cause the result to overflow.')
+  }
+  return Buffer.from(buf).fill(replacement, position, end)
+}
+
+function xor (x, y) {
+  if (x.length !== y.length) {
+    throw new Error('The length of two buffers is different')
+  }
+  let z = Buffer.alloc(x.length)
+  for (let i = 0; i < z.length; i ++) {
+    z[i] = x[i] ^ y[i]
+  }
+  return z
+}
+
+async function crack (iv, cipher, challenge) {
+  let original = Buffer.concat([iv, cipher])
+  let size = iv.length
+  let intermediary = Buffer.alloc(cipher.length)
+  let plain
+
+  console.log('--- Crack start ---')
+
+  for (let block = 0; block * size < cipher.length; block++) {
+    console.log('Current block:', block)
+
+    for (let padding = 1; padding <= size; padding++) {
+      console.log('Intermediary value:', intermediary.toString('hex'))
+      console.log('Current block: %s, padding: %s', block, padding)
+
+      let input = Buffer.concat([iv, cipher.slice(0, size * (block + 1))])
+      let found
+
+      for (let i = 1; i < padding; i++) {
+        input = replace(input, size * (block + 1) - i, Buffer.from([padding ^ intermediary[size * (block + 1) - i]]))
+      }
+
+      for (let i = 0; i < ALL_HEX.length; i++) {
+        let hex = ALL_HEX[i]
+        let sample = replace(input, size * (block + 1) - padding, Buffer.from(hex, 'hex'))
+        if (sample.equals(original)) {
+          log('key found: (backup)', `0x${hex}`)
+          found = hex
+          continue
+        }
+        if (await challenge(sample.slice(0, size), sample.slice(size))) {
+          log('key found:', `0x${hex}`)
+          found = hex
+          break
+        }
+        log('invalid:', `0x${hex}`)
+      }
+
+      if (!found) {
+        throw new Error('All the challenges failed.')
+      }
+      intermediary[size * (block + 1) - padding] = padding ^ parseInt(found, 16)
+      log.done()
+    }
+    console.log('Intermediary value:', intermediary.toString('hex'))
+  }
+
+  plain = xor(original.slice(0, intermediary.length), intermediary)
+  console.log('Plain text:', plain.toString())
+  console.log('Plain text (hex):', plain.toString('hex'))
+  console.log('---  Crack end  ---')
+
   return {
-    intermediary: Buffer.alloc(1),
-    plain: Buffer.alloc(1),
+    intermediary,
+    plain,
   }
 }
+
+exports.crack = crack