Electronic device manufacture and content provision

A method of preparing an electronic device to use stored content (e.g. firmware) comprises generating a delta data structure comprising data to modify an initial image in accordance with a first content data block; encrypting a resultant content data block using a corresponding encryption key; and providing the initial image and the encrypted block for embedding as stored content on the electronic device. A method of generating an update for an electronic device to use stored content, comprises acquiring a first delta data structure comprising data to modify an initial image in accordance with a first content data block to produce a current image; decrypting an encrypted block required by the first delta data structure using an encryption key to produce a first decrypted block, generating a second delta data structure comprising data to modify the current image in accordance with a second content data block; and providing the second delta data structure to the electronic device. A method of bringing a device to a specified level of content, comprises decrypting an encrypted block using a key and applying a delta data structure using the decrypted block to modify an image of content to the specified level.