Talk

Transfer sensitive messages and attachments safely.

This package is prepared for this deployment model:

• frontend/ -> static hosting (Tested in Cloudflare Pages)
• backend/ + nginx.conf + php-fpm.conf + php.ini + start.sh -> Serverless deployment (Tested in Alibaba Cloud FC)
• initial.sql -> MySQL schema

You can also deploy everything in a single server.

The frontend does not load JavaScript from any external source. It only loads these local files:

/assets/config.js
/assets/crypto.js
/assets/app.js

Project structure

initial.sql
README.md
LICENSE
frontend/
backend/
nginx.conf
php-fpm.conf
php.ini
start.sh

Security and storage model

Talk encrypts everything in the browser before upload. The backend stores only one opaque encrypted blob in talk_messages.ciphertext, which is a MEDIUMBLOB.

For each message:

1. The browser generates a random salt and derives key material from the passphrase using PBKDF2-SHA256.
2. The derived material is split into:
   • an AES-GCM key for browser-side encryption and decryption;
   • an access token that the backend verifies by HMAC with GLOBAL_SALT_3.
3. Each attachment is AES-GCM encrypted separately.
4. The browser builds this JSON:

{
  "message": "xxxxx",
  "files": [
    { "name": "xxx.ext", "bytelen": "12345" }
  ]
}

bytelen is the encrypted byte length of that attachment block.

5. The JSON is AES-GCM encrypted.
6. The browser assembles:

3-byte encrypted JSON length | encrypted JSON block | encrypted file block 1 | encrypted file block 2 | ...

7. The whole assembled block is AES-GCM encrypted again and uploaded as ciphertext.

When opening a message, the frontend uses XHR POST to fetch the complete encrypted blob from open.php. By default, the backend deletes the server-side copy during this successful open operation. If Allow multiple views was selected during creation, the server-side copy is kept until expiration. The browser then decrypts the outer block, decrypts the JSON block, displays message as raw HTML, and creates download links for each attachment. Attachment files are decrypted only when the user clicks a download link.

Limits

Defaults:

• Total original attachment size: 15 MiB (MAX_FILE_SUM_BYTES)
• Final encrypted blob size: at most 16 MiB minus 1 byte (MAX_CIPHERTEXT_BYTES, MySQL MEDIUMBLOB limit is 16,777,215 bytes)
• PHP / Nginx body upload size: 20 MiB

Database

Create a MySQL database and import initial.sql.

mysql -u USER -p DATABASE < initial.sql

The main table uses MEDIUMBLOB for ciphertext:

`ciphertext` mediumblob NOT NULL

Frontend deployment on Cloudflare Pages

Deploy the frontend/ directory.

Before deployment, edit frontend/assets/config.js:

window.TALK_CONFIG = {
  API_BASE: 'https://api.example.com/api',
  FRONTEND_BASE: 'https://talk.example.com',
  DEFAULT_PASSWORD: 'change-this-default-passphrase',
  PBKDF2_ITERATIONS: 210000,
  MAX_FILE_SUM_BYTES: 15 * 1024 * 1024,
  MAX_UPLOAD_BYTES: 16 * 1024 * 1024 - 1
};

Also edit frontend/_headers and replace this placeholder with your backend domain:

connect-src https://api.example.com

Backend deployment on Aliyun Function Compute

Deploy these files and directories as the backend code package root:

backend/
nginx.conf
php-fpm.conf
php.ini
start.sh

Use start.sh as the startup command. The default listening port is 9000. start.sh also accepts LISTEN_PORT or FC_SERVER_PORT.

Set these environment variables in Aliyun FC:

DB_HOST=your-mysql-host
DB_PORT=3306
DB_NAME=your-database
DB_USER=your-database-user
DB_PASSWORD=your-database-password
FRONTEND_URL=https://talk.example.com/
GLOBAL_SALT_3=replace-with-a-long-random-secret

Generate GLOBAL_SALT_3 with:

php -r "echo bin2hex(random_bytes(32)), PHP_EOL;"

Optional environment variables:

ALLOW_NO_ORIGIN_REQUESTS=false
TZ=America/Los_Angeles
PBKDF2_ITERATIONS=210000
MAX_FILE_SUM_BYTES=15728640
MAX_CIPHERTEXT_BYTES=16777215
CODE_LENGTH=8
DEFAULT_EXPIRE_DAYS=1
MAX_EXPIRE_DAYS=7
CREATE_LIMIT_PER_HOUR=120
CHECK_LIMIT_PER_HOUR=600

Editable config fallback

backend/function/config.php reads environment variables first. If you do not want to use env vars, you can directly edit fallback values in config.php, for example:

$DB_HOST = talk_config_value('DB_HOST', '127.0.0.1');
$DB_NAME = talk_config_value('DB_NAME', 'talk');
$DB_USER = talk_config_value('DB_USER', 'talk_user');
$DB_PASSWORD = talk_config_value('DB_PASSWORD', 'secret');
$FRONTEND_URL = talk_config_value('FRONTEND_URL', 'https://talk.example.com/');

The Nginx startup script injects environment variables into PHP through fastcgi_param. Values are Base64 encoded before insertion into the generated Nginx config so database passwords containing $, quotes, backslashes, or slashes do not break the config.

API endpoints

POST /api/create.php      multipart/form-data with ciphertext blob
GET  /api/meta.php?code=CODE
POST /api/open.php        JSON: {"code":"...","token":"..."}; returns application/octet-stream

Notes

• The passphrase is never sent to the backend. Leaving the passphrase field blank uses DEFAULT_PASSWORD from frontend/assets/config.js.
• The backend cannot decrypt messages or attachments.
• Messages are one-time read by default. If Allow multiple views is selected, a successful open.php call keeps the stored blob until expiration.
• Message output is intentionally rendered as raw HTML because this project explicitly preserves HTML tags in messages. Only share links with people you trust.