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abustanyabustany
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Add wasm build
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‎pkg/wasm/index.html

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<!doctype html>
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<html>
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<head>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width,initial-scale=1"/>
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<link rel="stylesheet" href="styles.css"/>
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</head>
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<body>
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<h1>lcp-decrypt</h1>
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<p class="notes">
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lcp-decrypt uses the provided key to decrypt an EPUB file protected
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using Readium LCP.
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</p>
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<form id="file-form">
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<div>
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<label for="input-file">Encrypted EPUB file</label>
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<input id="input-file" name="file" type="file" required />
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</div>
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<div>
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<label for="input-key">User key</label>
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<input id="input-key" name="key" type="text" required />
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</div>
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<div>
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<button id="button-submit" type="submit" disabled>Loading...</button>
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</div>
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</form>
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<p class="notes">
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The decrypted file will be downloaded to your computer.
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</p>
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<p class="notes">
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The decryption is done locally on your computer, the file is never
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uploaded anywhere.
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</p>
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<script src="wasm_exec.js"></script>
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<script src="main.js"></script>
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</body>
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</html>

‎pkg/wasm/main.js

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async function getLCP(go) {
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const WASM_URL = "lcp.wasm";
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let instance;
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if ("instantiateStreaming" in WebAssembly) {
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instance = (
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await WebAssembly.instantiateStreaming(fetch(WASM_URL), go.importObject)
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).instance;
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} else {
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const res = await fetch(WASM_URL);
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if (!res.ok) throw new Error(`unexpected status code: ${res.status}`);
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instance = (
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await WebAssembly.instantiate(await res.arrayBuffer(), go.importObject)
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).instance;
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}
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go.run(instance);
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return instance;
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}
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/**
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* @param {WebAssembly.Instance} lcp
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* @param {string} s
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* @returns {number} The memory address
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*/
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function newGoString(lcp, s) {
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const data = new TextEncoder().encode(s);
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return newGoBytes(lcp, data);
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}
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/**
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* @param {WebAssembly.Instance} lcp
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* @param {Uint8Array} data
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* @returns {number} The memory address
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*/
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function newGoBytes(lcp, data) {
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const { newBytes } = lcp.exports;
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const addr = newBytes(data.length);
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// Read *after* calling newBytes
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const u8mem = new Uint8Array(lcp.exports.memory.buffer);
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for (let i = 0; i < data.length; ++i) u8mem[addr + i] = data[i];
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return addr;
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}
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/**
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* @param {WebAssembly.Instance} lcp
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* @param {number} ptr
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* @returns {Uint8Array | null}
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*/
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function bytesFromGo(lcp, ptr) {
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const { memory, bytesSize } = lcp.exports;
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const size = bytesSize(ptr);
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if (!size) return null;
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return new Uint8Array(memory.buffer).subarray(ptr, ptr + size);
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}
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/**
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* @param {WebAssembly.Instance} lcp
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* @param {File} file
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* @param {string} key
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*/
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async function decrypt(lcp, file, key) {
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const { decrypt, freeBytes } = lcp.exports;
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const fileData = new Uint8Array(await file.arrayBuffer());
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console.log(fileData);
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const goFile = newGoBytes(lcp, fileData);
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const goKey = newGoString(lcp, key);
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let goOut;
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try {
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goOut = decrypt(goFile, goKey);
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const decryptedData = bytesFromGo(lcp, goOut);
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if (!decryptedData) throw new Error("no decrypted data");
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const blob = new Blob([decryptedData], { type: "application/epub+zip" });
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const link = document.createElement("a");
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link.href = URL.createObjectURL(blob);
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link.download = `decrypted.${file.name}`;
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document.body.appendChild(link);
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link.click();
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document.body.removeChild(link);
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URL.revokeObjectURL(link.href);
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} finally {
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freeBytes(goFile);
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freeBytes(goKey);
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if (goOut) freeBytes(goOut);
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}
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}
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async function main() {
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const go = new Go();
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const lcp = await getLCP(go);
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const submitButton = document.getElementById("button-submit");
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const resetSubmitButton = () => {
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submitButton.removeAttribute("disabled");
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submitButton.innerText = "Decrypt";
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};
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let busy = false;
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resetSubmitButton();
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document.getElementById("file-form").addEventListener("submit", (ev) => {
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ev.preventDefault();
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const formData = new FormData(ev.target);
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const file = formData.get("file");
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const key = formData.get("key");
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if (
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busy ||
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!file ||
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!(file instanceof File) ||
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!key ||
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typeof key !== "string"
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)
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return;
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busy = true;
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submitButton.setAttribute("disabled", "1");
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submitButton.innerText = "Decrypting...";
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decrypt(lcp, file, key)
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.catch((error) => {
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console.log(error);
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alert("There was an error decrypting the file");
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})
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.finally(() => {
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busy = false;
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resetSubmitButton();
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});
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});
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}
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main();

‎pkg/wasm/styles.css

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html {
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margin: 0;
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padding: 0;
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}
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body {
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margin: 0;
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padding: 0;
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font-family: sans-serif;
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display: grid;
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place-content: center;
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}
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h1 {
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font-size: 1.125rem;
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line-height: 1.75rem;
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}
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#file-form {
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display: grid;
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grid-auto-flow: row;
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gap: 0.5rem;
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}
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.notes {
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max-width: 40rem;
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}

‎pkg/wasm/wasm.go

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package main
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import (
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"bytes"
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"github.com/abustany/lcp-decrypt/pkg/lcp"
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)
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var handles = map[*byte][]byte{}
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func main() {
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}
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//export newBytes
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func newBytes(size int) *byte {
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if size == 0 {
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return nil
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}
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return newHandle(make([]byte, size))
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}
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func newHandle(b []byte) *byte {
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if len(b) == 0 {
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return nil
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}
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handles[&b[0]] = b
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return &b[0]
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}
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//export freeBytes
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func freeBytes(ptr *byte) {
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delete(handles, ptr)
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}
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//export bytesSize
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func bytesSize(ptr *byte) int {
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return len(handles[ptr])
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}
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//export decrypt
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func decrypt(inPtr *byte, userKeyHexPtr *byte) *byte {
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var out bytes.Buffer
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inputData := handles[inPtr]
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if err := lcp.Decrypt(&out, bytes.NewReader(handles[inPtr]), int64(len(inputData)), string(handles[userKeyHexPtr])); err != nil {
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panic(err.Error())
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}
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return newHandle(out.Bytes())
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}

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