Signed uploads

With signed uploads, you get to control who can and when can upload files to one of your Uploadcare projects. You need to generate a token on your backend, and a trusted user should use this token to upload a new file. It works with both Uploadcare File Uploader and Upload API.

Turning signed uploads on

Signed uploads can be turned on and off to an Uploadcare project, because it has a dedicated storage, Public and Private keys, and security settings.

Go to your Dashboard and select an existing project or create a new one. Open the project.
Click Enable next to Signed Uploads.

From now on, every request to Upload API should include a signature part (token). However, you'll still be able to upload files to your project on the website via the Dashboard.

Token generation

The token is called signature. Technically, it's a string sent along with your upload request. It requires your Uploadcare project's Secret Key.

The signature is an HMAC/SHA256 with two parameters:

secret_key — a generated key
expire — an expiration time message (string)

Here's how to make a signature on your backend in Python:

import time
import hashlib
import hmac

def generate_secure_signature(secret, expire):
    k, m = secret, str(expire).encode('utf-8')
    if not isinstance(k, (bytes, bytearray)):
        k = k.encode('utf-8')

    return hmac.new(k, m, hashlib.sha256).hexdigest()

# Expire in 30 min, e.g., 1454903856
expire = int(time.time()) + 60 * 30

# Secret key of your project
secret = 'project_secret_key'

# Example result: '9890adc8886d27c93befed595abfbca514b7592a88e2f64dbddbea2d369a68dc'
signature = generate_secure_signature(secret, expire)python

Making signature in Node.js:

const crypto = require('crypto');

function generateSignature(secret, expire) {
  const hmac = crypto.createHmac('sha256', secret);
  hmac.update(expire);
  return hmac.digest('hex');
}

// secret key
const secret = 'project_secret_key';

// define expiry (e.g. 120 seconds)
const expire = (Math.round(Date.now() / 1000) + 120).toString();
const signature = generateSignature(secret, expire);javascript

Making signature in Ruby:

require "openssl" # if necessary

def generate_signature(secret, expire_at)
OpenSSL::HMAC.hexdigest("SHA256", secret, expire_at.to_i.to_s)
end

secret = 'secret'
expire_at = Time.now + 60 * 2 # 2 minutes from now
generate_signature(secret, expire_at)ruby

`expire` explained

The expire string sets the expiration date and time or duration for a signature. It has a Unix time format.

The expire function in the Python example above adds a certain duration after the generation time. In this case, 30 minutes:

# Expire in 30 min, e.g., 1454903856
expire = int(time.time()) + 60 * 30
python

Signed uploads example

Request:

curl -F "UPLOADCARE_PUB_KEY=caa9d29da887ee88ffe6" \
     -F "signature=46f70d2b4fb6196daeb2c16bf44a7f1e" \
     -F "expire=1454903856" \
     -F "file=@image.jpg" \
     "https://upload.uploadcare.com/base/"bash

Response:

{
  "file": "c0d776d4-8c8e-47df-9e92-03b68b99c2ba"
}json

To work with File Uploader, install and configure it first. Then specify the secure signature and secure expire options.

Possible errors

Both signature and an active expire are required for every upload request and should be valid. The list of possible errors:

[HTTP 400] 'signature' is required.json

[HTTP 400] 'expire' is required.json

If expire is not a valid Unix timestamp:

[HTTP 400] 'expire' must be a UNIX timestamp.json

If your signature has expired, i.e., expire < now:

[HTTP 403] Expired signature.json

If signature is incorrect:

[HTTP 403] Invalid signature.json