can you output a version of bitmessage that will run in a browser using webassemble?
We are going to create a simplified version of Bitmessage that can run in a browser using WebAssembly.
However, note that Bitmessage is a complex system and we cannot replicate the entire system in a short example.
Instead, we will focus on a minimal example that demonstrates:
– Generating a Bitmessage address (which involves ECDSA key generation)
– Creating a simple message structure
– Signing the message with the private key
– Verifying the signature with the public key
We will use the WebCrypto API for cryptographic operations and WebAssembly for performance-critical parts.
But note: WebCrypto is already available in browsers and we don’t necessarily need WebAssembly for ECDSA.
However, if we want to do heavy processing (like proof of work) then WebAssembly would be useful.
Since the problem asks for WebAssembly, we will use it for the proof of work (PoW) part.
Steps:
1. Generate an ECDSA key pair (using WebCrypto).
2. Create a Bitmessage address from the public key.
3. Create a message and sign it (using WebCrypto).
4. Implement a simple proof of work (PoW) in WebAssembly (C/Rust compiled to WASM) for the message.
However, note that the original Bitmessage uses a different addressing scheme and PoW algorithm.
Let’s break down:
Addressing in Bitmessage:
– It uses ECDSA (secp256k1) for the key pair.
– The address is base58 encoded and includes:
version + stream + public key (in secp256k1) + checksum
We will simplify:
Address = base58(version + stream + publicKey + checksum)
But the checksum is the first 4 bytes of sha256(sha256(version + stream + publicKey))
5. Proof of Work: Bitmessage uses a memory-hard PoW (hashing with increasing nonce until the hash meets a target).
We will implement a simple SHA256 PoW (non memory-hard) for demonstration.
Due to the complexity, we’ll break the project into parts:
Part 1: JavaScript (using WebCrypto for keys and signing)
Part 2: WebAssembly module (for PoW)
However, note that the WebCrypto API does not support secp256k1 in all browsers. So we might use a WASM library for that too?
But the problem says to use WebAssembly. We can use a WASM version of secp256k1 if needed.
Alternatively, we can use the ‘elliptic’ library (JavaScript) but that is not WASM.
Since the requirement is to run in the browser and use WebAssembly, we can:
– Use a precompiled WASM module for secp256k1 (like from `libsecp256k1` compiled via Emscripten) for key generation and signing?
– But the problem does not require the entire Bitmessage, just a version that runs in the browser with WASM.
Considering time, we will do:
Step 1: Generate key pair using WebCrypto (if supported) or fallback to a WASM secp256k1 if not. But let’s assume we are using a supported browser (Chrome, Firefox with experimental features).
However, currently WebCrypto only supports NIST curves. So we must use a WASM library for secp256k1.
Therefore, we will use a WASM module for:
– secp256k1 key generation
– signing
– address generation
And another WASM module for PoW.
But note: We are limited by the context of this response. We can write the JavaScript to load a WASM module and then use it.
However, we cannot compile and include the WASM binary here. Instead, we will write the C code for the PoW and the secp256k1 functions and then show how to use it.
Alternatively, we can use an existing WASM library? But we are to output the code.
Given the constraints, we will:
a) Write a simple C program for PoW (nonce increment until the hash meets a difficulty) and compile it to WASM.
b) Use a JavaScript library for secp256k1 (like elliptic) for the rest, but that doesn’t use WASM. So we must write our own WASM for secp256k1? That is complex.
Considering the scope, let’s focus on PoW in WASM and use elliptic (pure JS) for the ECDSA. Then we can replace elliptic with a WASM-based secp256k1 later if needed.
The problem says “using webassembly”, so we must use it at least for one part.
We’ll do:
– PoW in WASM (C code compiled to WASM)
Steps for PoW in C:
void pow(char *input, int input_length, unsigned long long nonce_start, unsigned long long *nonce_result)
{
// We’ll assume the input is a string and we append the nonce to it.
// We are looking for a nonce such that sha256(input + nonce) has a certain number of leading zeros.
// We’ll set a target: first 2 bytes (16 bits) are zero -> 16 bits of difficulty (for example)
unsigned char hash[32];
unsigned long long nonce = nonce_start;
while (1) {
// Create a buffer: input + nonce (8 bytes in little-endian? but we don’t care about endianness for the nonce, we just append bytes)
char buffer[input_length + 8];
memcpy(buffer, input, input_length);
memcpy(buffer+input_length, &nonce, 8);
// Compute sha256
sha256(buffer, input_length+8, hash);
// Check the first 2 bytes
if (hash[0] == 0 && hash[1] == 0) {
*nonce_result = nonce;
return;
}
nonce++;
}
}
But we need a SHA256 implementation in C. We can use one from OpenSSL, but we are in a standalone C. Let’s use a simple one.
We can use a public domain SHA256 implementation (like from https://github.com/amosnier/sha-2).
However, due to the length, we’ll use a minimal one.
Alternatively, we can use the OpenSSL SHA256 if we are compiling with Emscripten? But we want to be standalone.
We’ll include a SHA256 implementation in the C file.
But note: This example is for demonstration only. The actual Bitmessage PoW is different (it uses a memory-hard function, but we are doing a simple one).
We’ll write the C code for PoW with a simple SHA256.
Part 3: JavaScript code to:
– Load the WASM module for PoW.
– Use the elliptic library (for secp256k1) to generate keys and create an address.
– Create a message and sign it.
– Do PoW on the message using the WASM module.
Let’s outline the JavaScript code:
Step 1: Include the elliptic library and a base58 library.
We can use: https://cdnjs.cloudflare.com/ajax/libs/elliptic/6.5.4/elliptic.min.js
and: https://cdnjs.cloudflare.com/ajax/libs/base58/2.0.0/base58.min.js
Step 2: Load the WASM module for PoW.
Step 3: Generate a key pair with elliptic.
var ec = new elliptic.ec(‘secp256k1’);
var keyPair = ec.genKeyPair();
var publicKey = keyPair.getPublic(‘hex’);
var privateKey = keyPair.getPrivate(‘hex’);
Step 4: Create an address.
// Simplified: version (1 byte) + stream (1 byte) + publicKey (65 bytes for uncompressed) + checksum (4 bytes)
// We’ll use version 0x01 and stream 0x01.
var version = new Uint8Array([0x01]);
var stream = new Uint8Array([0x01]);
var pubKeyBytes = hexToBytes(publicKey); // we need a function to convert hex string to bytes
var payload = new Uint8Array(version.length + stream.length + pubKeyBytes.length);
payload.set(version, 0);
payload.set(stream, 1);
payload.set(pubKeyBytes, 2);
// Double SHA256 for checksum
var firstHash = new Uint8Array(32);
var secondHash = new Uint8Array(32);
// Use WebCrypto or a JS SHA256 for the checksum?
// We can use the WebCrypto for SHA256 if available, but for simplicity we can use a JS library or the elliptic utils?
// elliptic doesn’t have SHA256, so we use WebCrypto.
// We’ll use a function to compute double SHA256
async function doubleSha256(data) {
const first = await crypto.subtle.digest(‘SHA-256’, data);
const second = await crypto.subtle.digest(‘SHA-256’, first);
return new Uint8Array(second);
}
const checksum = (await doubleSha256(payload)).slice(0,4);
const addressBytes = new Uint8Array(payload.length + 4);
addressBytes.set(payload, 0);
addressBytes.set(checksum, payload.length);
// Then base58 encode
const address = base58.encode(addressBytes);
Step 5: Sign a message.
const message = “Hello, world!”;
const signature = keyPair.sign(message);
Step 6: Do PoW on the message.
We are going to do PoW on the message string. We’ll convert the message to bytes and then call the WASM PoW function.
The WASM function expects:
input: pointer to the message bytes
input_length: length of the message
nonce_start: starting nonce (we can start at 0)
returns: the nonce that satisfies the PoW
We’ll set the target to 2 leading zero bytes (so 16 bits of work).
Step 7: Display the results.
However, note: The actual Bitmessage protocol does PoW on the entire message (which includes sender, recipient, message content, etc.) and the target is adjusted.
We are simplifying.
Implementation of the WASM PoW:
We’ll write the C code and then compile it with Emscripten.
C code (pow.c):
#include <stdint.h>
#include <string.h>
#include “sha256.h” // We need to include a SHA256 implementation
// We’ll put the SHA256 implementation here? Or include a separate file.
// We are going to use a simple SHA256 implementation that we have in the same file.
// Copy a public domain SHA256 implementation here (we’ll use one from: https://github.com/amosnier/sha-2)
// We’ll include the code from https://github.com/amosnier/sha-2/blob/master/sha-256.c but we have to adapt for our use.
// Instead, we can use a minimal one. We’ll use the one from the above link.
// We are going to include the entire sha-256.c and sha-256.h here.
// But due to the length, we’ll show a simplified version? Actually, we can use the one from the repo.
// We are going to assume we have the sha-256.c and sha-256.h in the same directory.
// But we are going to write a single file for simplicity.
// We’ll copy the code from the repo’s sha-256.c and sha-256.h and put it in one file.
// However, the problem is the length. We’ll write a minimal SHA256 that works.
// Alternatively, we can use Emscripten’s built-in SHA256? But we want to be standalone.
// We’ll use a small SHA256 implementation that we write ourselves? That is error prone.
// Instead, we’ll use the OpenSSL SHA256 if we are compiling with Emscripten? We can link against the system OpenSSL? Not available.
// We’ll use the one from the above repo.
// We are going to copy the code from the repo and put it in one file.
// Due to the character limit, we cannot include the entire sha256 implementation here.
// Instead, we’ll provide a link and then write the PoW function that uses it.
// We’ll write the function as:
void sha256(const unsigned char *data, size_t len, unsigned char *out) {
// using the implementation from the repo
struct Sha256 sha;
sha256_init(&sha);
sha256_write(&sha, data, len);
sha256_result(&sha, out);
}
// Then our pow function:
void EMSCRIPTEN_KEEPALIVE pow(char *input, int input_length, unsigned long long nonce_start, unsigned long long *nonce_result) {
unsigned char hash[32];
unsigned long long nonce = nonce_start;
char *buffer = (char*)malloc(input_length + 8);
if (!buffer) {
// handle error
return;
}
memcpy(buffer, input, input_length);
while (1) {
// Append the nonce (as 8 bytes in little-endian? We don’t care as long as consistent)
// We’ll use little-endian for the nonce in the buffer.
for (int i = 0; i < 8; i++) {
buffer[input_length + i] = (nonce >> (i * 8)) & 0xFF;
}
sha256((unsigned char*)buffer, input_length+8, hash);
// Check the first 2 bytes for zeros
if (hash[0] == 0 && hash[1] == 0) {
*nonce_result = nonce;
free(buffer);
return;
}
nonce++;
// Break if nonce overflows? We are using unsigned long long, so it will wrap around.
// We don’t handle overflow in this example.
}
}
We also need to export the pow function to JavaScript.
We’ll compile with:
emcc pow.c -o pow.js -s EXPORTED_FUNCTIONS='[“_pow”]’ -s EXPORTED_RUNTIME_METHODS='[“ccall”, “cwrap”]’
This will generate pow.js and pow.wasm.
Then in JavaScript:
// Load the wasm module
const Module = require(‘./pow.js’); // or in the browser, we use the generated .js file
// Wait for the module to be ready
Module.onRuntimeInitialized = function() {
// Now we can use Module.ccall or Module.cwrap
const pow = Module.cwrap(‘pow’, ‘void’, [‘array’, ‘number’, ‘number’, ‘number’]);
// But note: the pow function writes the result to a pointer (the last argument). We need to allocate memory for the result.
// Alternatively, we can use:
// pow(input, input_length, nonce_start, result_ptr)
// How to use:
const input = “Hello, world!”;
const input_length = input.length;
const nonce_start = 0;
// We need to copy the input string to the module’s memory.
const buffer = new Uint8Array(input_length + 8);
for (let i = 0; i < input_length; i++) {
buffer[i] = input.charCodeAt(i);
}
// We are going to pass the input as a pointer to the buffer, and then the pow function will write the nonce at the given pointer.
// Allocate memory for the result (one unsigned long long, 8 bytes)
const resultPtr = Module._malloc(8);
// Call pow
Module.ccall(‘pow’, null,
[‘array’, ‘number’, ‘number’, ‘number’],
[buffer, input_length, nonce_start, resultPtr]
);
// Read the result
const nonce = Module.HEAPU64[resultPtr / 8]; // because HEAPU64 views memory as 8-byte chunks
// Free
Module._free(resultPtr);
console.log(“Nonce found:”, nonce);
};
However, note: the pow function in C expects the input as a char* and then appends 8 bytes for the nonce. We allocated a buffer of input_length+8 and passed the pointer to the buffer. But we also passed input_length (the original length). The C function will write the nonce in the last 8 bytes? Actually, it writes the nonce in the buffer we passed? But we don’t need the buffer back.
We are only interested in the nonce.
But note: the buffer we passed to C is a copy? Actually, we are passing the pointer to the buffer in JavaScript. The C function will write to that buffer. But we allocated the buffer in JavaScript, not in the module’s memory. This might not work.
We need to allocate the buffer in the module’s memory and copy the input.
Alternatively, we can use:
const inputPtr = Module._malloc(input_length + 8);
Module.HEAPU8.set(inputBytes, inputPtr);
then call pow(inputPtr, input_length, nonce_start, resultPtr);
and in C, we write the nonce in the last 8 bytes? Actually, we write the nonce in the buffer at offset input_length to input_length+8? But then we don’t return that buffer. We only return the nonce.
So we don’t need to pass the buffer back.
We’ll change the C function to take the input without the nonce space, and then we create a new buffer inside the C function (which we did with malloc) and then free it.
We already did that in the C code above.
Therefore, we don’t need to pre-allocate the buffer for the nonce in the input. We only need the input and its length.
So the JavaScript code should be:
const input = “Hello, world!”;
const inputBytes = new TextEncoder().encode(input); // Uint8Array
const inputPtr = Module._malloc(inputBytes.length);
Module.HEAPU8.set(inputBytes, inputPtr);
const resultPtr = Module._malloc(8);
Module.ccall(‘pow’, null,
[‘number’, ‘number’, ‘number’, ‘number’],
[inputPtr, inputBytes.length, 0, resultPtr]
);
const nonce = Module.HEAPU64[resultPtr / 8];
Module._free(inputPtr);
Module._free(resultPtr);
But note: the function signature in ccall:
[‘number’, ‘number’, ‘number’, ‘number’] for the arguments: (char* input, int input_length, unsigned long long nonce_start, unsigned long long* nonce_result)
And the function name is ‘pow’. We exported it as ‘_pow’, but in C we declared it as ‘pow’. The leading underscore is added by Emscripten.
We should use the function name as ‘_pow’ in the ccall? Or without the underscore? The Emscripten documentation says we use the name without the underscore.
Actually, the EXPORTED_FUNCTIONS we used: ‘_pow’ -> then the function in JavaScript will be available as _pow or we can use ccall with ‘pow’?
We’ll try without the underscore.
Alternatively, we can wrap it with:
const pow = Module.cwrap(‘pow’, null, [‘number’, ‘number’, ‘number’, ‘number’]);
pow(inputPtr, inputBytes.length, 0, resultPtr);
But note: the nonce_start is a 64-bit integer, which we are passing as a ‘number’. But in JavaScript, numbers are 64-bit floats and only 53 bits for integers. We can use BigInt? But the ccall doesn’t support BigInt for 64-bit integers?
We have to split the nonce_start into two 32-bit integers? Or we can pass it as a single 64-bit integer by using setValue.
Alternatively, we can change the nonce_start to be passed by reference? Or we can pass it as a string?
We’ll change the C function to take nonce_start as two 32-bit integers (low and high). But that complicates.
Instead, we can use the BigInt support in Emscripten: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.html#bigint-integration
But we are using ccall which doesn’t support BigInt?
We’ll change the function to take nonce_start as a double and then cast to uint64_t? That might lose precision.
Alternatively, we can pass nonce_start as a pointer to a 64-bit integer? Then we can set it with setValue.
We’ll change the function to:
void pow(char *input, int input_length, unsigned long long *nonce_start, unsigned long long *nonce_result)
And then we pass nonce_start as a pointer to a 64-bit integer.
Then in JavaScript:
const nonceStart = 0; // we want to start at 0
const nonceStartPtr = Module._malloc(8);
Module.HEAPU64.set([BigInt(nonceStart)], nonceStartPtr / 8);
// then call pow(inputPtr, input_length, nonceStartPtr, resultPtr);
But that requires two mallocs and frees.
Considering the complexity, and since nonce_start is a starting point and we are not worried about 64-bit integers beyond 2^53, we can pass it as a number and cast to uint64_t in C. The nonce will be within 2^53 in a reasonable time.
So we’ll leave the function as:
void pow(char *input, int input_length, unsigned long long nonce_start, unsigned long long *nonce_result)
and in JavaScript, we pass nonce_start as a number (which is 0).
But if nonce_start is beyond 2^53, it might be rounded. For our example, we start at 0.
We’ll assume nonce_start is within the safe integer range.
So the JavaScript call remains.
Now, we put it all together in an HTML file.
However, note that the PoW function might run for a long time and block the main thread. We should run it in a Web Worker? But that is beyond the scope.
We’ll run it in the main thread for simplicity.
Steps:
– Include the elliptic and base58 libraries.
– Load the WASM module (pow.js) and wait for it to initialize.
– Generate the key pair and address.
– Sign the message.
– Do PoW on the message.
We’ll write the code accordingly.
Due to the complexity and length, we cannot write the entire code here. But we can outline.
Let’s write a simplified version without the actual WASM module loading for PoW? We’ll simulate the PoW with a JavaScript function? But the requirement is to use WASM.
We’ll write the code as if we have the WASM module.
We’ll assume we have the WASM module compiled and available at `pow.wasm`.
We’ll use the Emscripten generated JavaScript to load it.
We’ll also note that the SHA256 implementation in the WASM module is from the public domain and we must include the license.
Given the constraints, we provide the code outline.
We’ll break the code into parts.
Part A: HTML and libraries
index.html:
<!DOCTYPE html>
<html>
<head>
<title>Bitmessage in Browser</title>
https://cdnjs.cloudflare.com/ajax/libs/elliptic/6.5.4/elliptic.min.js
https://cdnjs.cloudflare.com/ajax/libs/base58/2.0.0/base58.min.js
http://pow.js <!– the Emscripten generated JS –>
</head>
<body>
<script>
// We’ll write our code here
</script>
</body>
</html>
Part B: JavaScript code in the script tag.
// Wait for the Module to be ready
Module.onRuntimeInitialized = async function() {
// Step 1: Generate key pair
const ec = new elliptic.ec(‘secp256k1’);
const keyPair = ec.genKeyPair();
const publicKey = keyPair.getPublic(‘hex’);
const privateKey = keyPair.getPrivate(‘hex’);
// Convert public key to bytes (uncompressed)
const pubKeyBytes = hexToBytes(publicKey); // we’ll write hexToBytes
// Step 2: Create address
const version = new Uint8Array([0x01]);
const stream = new Uint8Array([0x01]);
const payload = new Uint8Array(version.length + stream.length + pubKeyBytes.length);
payload.set(version, 0);
payload.set(stream, 1);
payload.set(pubKeyBytes, 2);
// Compute checksum
const checksum = (await doubleSha256(payload)).slice(0,4);
const addressBytes = new Uint8Array(payload.length + 4);
addressBytes.set(payload, 0);
addressBytes.set(checksum, payload.length);
const address = base58.encode(addressBytes);
console.log(“Address:”, address);
// Step 3: Sign a message
const message = “Hello, world!”;
const signature = keyPair.sign(message);
// Step 4: Do PoW on the message
// We are going to do PoW on the message string
const messageBytes = new TextEncoder().encode(message);
const messagePtr = Module._malloc(messageBytes.length);
Module.HEAPU8.set(messageBytes, messagePtr);
const resultPtr = Module._malloc(8);
// We start nonce at 0
Module.ccall(‘pow’, null,
[‘number’, ‘number’, ‘number’, ‘number’],
[messagePtr, messageBytes.length, 0, resultPtr]
);
const nonce = Module.HEAPU64[resultPtr / 8];
Module._free(messagePtr);
Module._free(resultPtr);
console.log(“PoW nonce:”, nonce);
};
// Helper functions
function hexToBytes(hex) {
// … convert hex string to Uint8Array
}
async function doubleSha256(data) {
// … using WebCrypto
}
We’ll implement the helper functions.
However, note: the elliptic public key is in hex format, and it is in uncompressed form by default?
`keyPair.getPublic(‘hex’)` returns the uncompressed public key (04 + x + y) and is 130 hex digits (65 bytes).
So we can do:
function hexToBytes(hex) {
const bytes = [];
for (let i = 0; i < hex.length; i += 2) {
bytes.push(parseInt(hex.substr(i, 2), 16));
}
return new Uint8Array(bytes);
}
async function doubleSha256(data) {
const first = await crypto.subtle.digest(‘SHA-256’, data);
const second = await crypto.subtle.digest(‘SHA-256’, first);
return new Uint8Array(second);
}
But note: WebCrypto’s digest returns an ArrayBuffer.
This should work.
Finally, we need to compile the C code to WASM.
We’ll provide the C code for pow.c and sha256.c and sha256.h.
We’ll use the SHA256 implementation from: https://github.com/amosnier/sha-2
We’ll download sha-256.c and sha-256.h.
Then in pow.c:
#include “sha-256.h”
void EMSCRIPTEN_KEEPALIVE pow(char *input, int input_length, unsigned long long nonce_start, unsigned long long *nonce_result) {
unsigned char hash[32];
unsigned long long nonce = nonce_start;
char *buffer = (char*)malloc(input_length + 8);
if (!buffer) {
// handle error
return;
}
memcpy(buffer, input, input_length);
while (1) {
// Append nonce as 8 bytes in little-endian
for (int i = 0; i < 8; i++) {
buffer[input_length + i] = (nonce >> (i * 8)) & 0xFF;
}
calc_sha_256(hash, (const unsigned char*)buffer, input_length+8);
// Check the first 2 bytes
if (hash[0] == 0 && hash[1] == 0) {
*nonce_result = nonce;
free(buffer);
return;
}
nonce++;
}
}
And then compile:
emcc pow.c sha-256.c -o pow.js -s EXPORTED_FUNCTIONS='[“_pow”]’ -s EXPORTED_RUNTIME_METHODS='[“ccall”, “cwrap”, “malloc”, “free”]’ -s ALLOW_MEMORY_GROWTH=1
Note: We allow memory to grow because the PoW might use a lot of memory? Actually, we only malloc a buffer of input_length+8, so it’s small.
We then have pow.js and pow.wasm.
We put them in the same directory as the HTML.
Then open the HTML.
This is a very simplified version of Bitmessage in the browser using WebAssembly for PoW.
Note: The actual Bitmessage protocol is much more complex and this is just a demonstration.
We have not implemented the entire Bitmessage protocol, only address generation, signing, and a simple PoW.
Also, the elliptic curve operations are in JavaScript, not WASM, but that can be replaced if needed.
This should meet the requirement of using WebAssembly in the browser for part of the Bitmessage functionality.
Creating a complete Bitmessage implementation for the browser using WebAssembly is a complex task that requires significant cryptographic and networking development. Below is a conceptual implementation demonstrating key components adapted for browser execution. This example focuses on:
- WebAssembly-based Proof-of-Work (PoW)
- Elliptic curve cryptography (secp256k1)
- Address generation
- Message packaging
Step 1: WebAssembly Proof-of-Work (C++ → WASM)
pow.cpp (Compiles to WASM via Emscripten)
cpp
#include <emscripten.h>
#include <string.h>
#include "sha256.h" // Your SHA-256 implementation
extern "C" {
EMSCRIPTEN_KEEPALIVE
uint64_t doPow(uint8_t *data, uint32_t len, uint64_t target) {
uint64_t nonce = 0;
uint8_t hash[32];
uint8_t buffer[256];
while (true) {
// Prepare data + nonce
memcpy(buffer, data, len);
memcpy(buffer + len, &nonce, sizeof(nonce));
// Calculate SHA-256
sha256(buffer, len + sizeof(nonce), hash);
// Check if hash meets target (first 64 bits)
if (memcmp(hash, &target, sizeof(target)) <= 0) {
return nonce;
}
nonce++;
}
}
}
Compile with:em++ pow.cpp -O3 -s WASM=1 -s EXPORTED_FUNCTIONS="['_doPow']" -o pow.js
Step 2: JavaScript Bitmessage Components
bitmessage.js (Browser-side logic)
javascript
import { ec as EC } from 'elliptic';
import base58 from 'bs58';
import { sha256 } from 'js-sha256';
// Initialize Emscripten WASM module
import init, { doPow } from './pow.js';
class Bitmessage {
constructor() {
this.ec = new EC('secp256k1');
this.powModule = null;
}
async init() {
this.powModule = await init(); // Load WASM
}
// Generate Bitmessage address
generateAddress() {
const keyPair = this.ec.genKeyPair();
const pubKey = keyPair.getPublic('hex');
// Address = Version (1) + Stream (0) + PubKey + Checksum
const payload = new Uint8Array([
0x01, 0x00,
...Buffer.from(pubKey, 'hex')
]);
const checksum = sha256.array(sha256.array(payload)).slice(0, 4);
const address = base58.encode(Buffer.concat([payload, checksum]));
return { address, privateKey: keyPair.getPrivate('hex') };
}
// Create message with PoW
async createMessage(senderPrivKey, recipientAddr, content) {
// 1. Serialize message metadata
const meta = JSON.stringify({ recipientAddr, timestamp: Date.now() });
// 2. Sign content
const key = this.ec.keyFromPrivate(senderPrivKey);
const signature = key.sign(content).toDER('hex');
// 3. Prepare PoW input
const powInput = new TextEncoder().encode(meta + content + signature);
// 4. Compute PoW nonce via WASM
const target = 0x0000FFFF; // Example difficulty
const nonce = doPow(
new Uint8Array(powInput),
powInput.length,
BigInt(target)
);
// 5. Package final message
return {
meta,
content,
signature,
nonce: nonce.toString()
};
}
}
// Usage
const bm = new Bitmessage();
await bm.init();
// Generate address
const { address, privateKey } = bm.generateAddress();
console.log("Your address:", address);
// Send message
const message = await bm.createMessage(
privateKey,
"BM-2cUZb5Ae7CJx9B3d7XZJqK3",
"Hello from WebAssembly!"
);
Key Components Explained:
- WebAssembly PoW:
- Heavy computational work (mining) offloaded to WASM
- Uses SHA-256 adapted for Emscripten
doPow()finds nonce matching target difficulty
- Cryptography:
- elliptic library for secp256k1 keys and signatures
- Address format: Base58(Version + Stream + PubKey + Checksum)
- Message Structure:
- Metadata (recipient, timestamp)
- Content + ECDSA signature
- PoW nonce proving computational work
Limitations & Challenges:
- Networking: Browser WebSocket connections to PyBitmessage nodes required
- Encryption: AES-CBC not shown (needs WebCrypto integration)
- Scalability: WebAssembly memory limits for large objects
- Security: Private key handling in browser is risky
Required Libraries:
- Elliptic:
npm install elliptic - bs58:
npm install bs58 - js-sha256:
npm install js-sha256
This is a proof-of-concept demonstrating core Bitmessage functionality in the browser. A full implementation would require peer-to-peer networking via WebSockets/WebRTC and additional cryptographic components. For production use, consider security implications of running decentralized messaging in a browser environment.
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