p256dh

p256dh is a cryptographic parameter used in the Web Push Notification protocol to ensure secure communication between a server and a client's device. It represents the public key component of an Elliptic Curve Diffie-Hellman (ECDH) key exchange, specifically utilizing the P-256 curve, which is also known as prime256v1 or secp256r1.

In the context of web push notifications, the p256dh value is generated on the client side when a user subscribes to push notifications through a web browser. This public key is then transmitted to the server and stored as part of the subscription information. When the server sends push messages, it uses the corresponding private key to encrypt the payload, ensuring that only the intended recipient can decrypt and read the message.

The p256dh parameter is typically encoded in a URL-safe base64 format, facilitating easy transmission over HTTP. This key, along with the auth secret, forms the core of the end-to-end encryption mechanism, bolstering privacy and security for push notifications.

Overall, p256dh is a crucial element in the web push ecosystem, enabling secure, authenticated, and confidential communications between servers and client devices. Its adoption is standardized across modern browsers that support the Push API and the Application Server Keys specification.