In a content protection scheme, and in response to a request for a content segment received by a server, the server generates and associates with the segment a message that confers entitlement to a session-specific key from which one or more decryption keys may be derived. The decryption keys are useful to decrypt the segment at runtime as it is about to be rendered by a player. Before delivery, the server encrypts the segment to generate an encrypted fragment, and it then serves the encrypted fragment (and the message) in response to the request. At the client, information in the message is used to obtain the session-specific key. Using that key, the decryption keys are derived, and those keys are then used to decrypt the received encrypted fragment. The decryption occurs at runtime. The approach protects content while in transit to and at rest in the client browser environment.