CP-HMAC request signing

Every request to /v1/* is signed with your API key secret. The secret itself never goes over the wire. The official clients handle this for you; this page is for anyone writing their own.

Header

Authorization: CP-HMAC key=<key_id>, ts=<unix_seconds>, nonce=<nonce>, sig=<hex>

What gets signed

string = METHOD + "\n" + PATH_WITH_QUERY + "\n" + ts + "\n" + nonce + "\n" + hex(sha256(body))
sig    = hex(HMAC-SHA256(secret, string))

• METHOD: GET, POST, and so on.
• PATH_WITH_QUERY: the path and query string exactly as they'll be sent: /v1/invoices?status=paid&limit=50. The scheme and host aren't signed.
• The body is signed byte for byte. Sign the exact JSON string you'll send, not a re-serialized object.
• For requests without a body, hex(sha256("")) = e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.

import { createHash, createHmac, randomBytes } from "node:crypto";

export function sign(keyId, secret, method, pathWithQuery, body = "") {
  const ts = Math.floor(Date.now() / 1000).toString();
  const nonce = randomBytes(16).toString("hex");
  const bodyHash = createHash("sha256").update(body).digest("hex");
  const sig = createHmac("sha256", secret)
    .update(`${method}\n${pathWithQuery}\n${ts}\n${nonce}\n${bodyHash}`)
    .digest("hex");
  return `CP-HMAC key=${keyId}, ts=${ts}, nonce=${nonce}, sig=${sig}`;
}

function cp_sign(string $keyId, string $secret, string $method, string $pathWithQuery, string $body = ''): string {
    $ts = (string) time();
    $nonce = bin2hex(random_bytes(16));
    $str = $method . "\n" . $pathWithQuery . "\n" . $ts . "\n" . $nonce . "\n" . hash('sha256', $body);
    $sig = hash_hmac('sha256', $str, $secret);
    return "CP-HMAC key=$keyId, ts=$ts, nonce=$nonce, sig=$sig";
}

import hashlib, hmac, secrets, time

def cp_sign(key_id: str, secret: str, method: str, path_with_query: str, body: bytes = b"") -> str:
    ts = str(int(time.time()))
    nonce = secrets.token_hex(16)
    msg = f"{method}\n{path_with_query}\n{ts}\n{nonce}\n{hashlib.sha256(body).hexdigest()}"
    sig = hmac.new(secret.encode(), msg.encode(), hashlib.sha256).hexdigest()
    return f"CP-HMAC key={key_id}, ts={ts}, nonce={nonce}, sig={sig}"

sig := cryptopayclient.SignRequest(secret, "POST", "/v1/invoices", ts, nonce, body)
req.Header.Set("Authorization", fmt.Sprintf("CP-HMAC key=%s, ts=%d, nonce=%s, sig=%s", keyID, ts, nonce, sig))

Test vectors

Check your implementation against these values. All four official clients are tested against the same ones.

Getting a 401?

Every signature failure returns 401 unauthorized with the same message; the server won't tell you exactly what's wrong. Common causes:

• the server clock has drifted by more than 5 minutes (enable NTP);
• a different path was signed: missing the query string, or with parameters in a different order;
• the body was re-serialized after signing;
• a nonce was reused;
• the key has been revoked.

403 merchant_suspended means the signature is valid, but the merchant is suspended.

Keys

• Create keys in the dashboard under “Keys & webhooks.” The secret is shown only once.
• Up to 10 keys can be active at once. To rotate: create a new key, switch your server over, then revoke the old one. Revocation takes effect immediately.
• Keep the secret in a secrets manager or a server environment variable, never in code or git.
• The rate limit is about 20 requests per second per merchant, with headroom for bursts; exceeding it returns 429 rate_limited.