Evolution note we may want to generalize the

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Evolution Note: We may want to generalize the architecture to sup- port multiple certificate formats rather than require XML-SEC. For example, the x509 standard for digital certificates provides roughly the same capabilities and could be used as an alternative. 25
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5.2 Booting a Node Each MA runs a boot server that is contacted by its client nodes whenever they reboot. Each node boots from an immutable filesystem (e.g., a CD-ROM) that bootstraps a boot manager onto the node. The boot manager, in turn, contacts the MA’s boot server to download all necessary code and configuration information needed to fully boot the node, as described below. The immutable filesystem also includes a set of certificate authority (CA) certificates corresponding to the well- known root public keys. This set of CA certificates is used by the boot manager to authenticate the boot server. Note that the bootstraping code and certificates can be openly distributed on a CD, for example, and used to boot any node. The information is MA-specific, but not node-specific. When a node is registered with the MA, a secret key is generated for that node, stored in the MA database, then exported to the node as part of the node configu- ration file (see Section 4.1). The node key can subsequently be used as a shared secret by the boot manager to authenticate the node to the MA. The node owner must copy the configuratoin file onto a write-protected device, typically a device with mechanical write protection capability. We assume that the node owner phys- ically secures the node so that the write-protected device cannot be accessed by unauthorized users. When a node boots, the boot manager contacts the MA securely (using SSL) to load all necessary code and current configuration information. The node uses the set of CA certificates to authenticate the MA’s boot server, and then uses its secret node key to authenticate itself to the boot server via HMAC. The authenticated node then queries the boot server to determine whether the node should boot into its standard execution mode or a restricted “debug” mode that allows only MA administrators to access the machine. This process is described in more detail in Section 4.8.2. 5.3 Creating a Slice Slice creation is a multi-stage process, involving the node owner, a slice creation service, and a slice authority. The process includes the following steps: The node owner acquires an SSL certificate for the PLC slice authority and/or any other trusted slice authorities through an off-line process. For each slice authority, the owner creates a configuration file that identifies a server for the slice authority and includes the SSL certificate for that author- ity. The owner script that is run by the node manager whenever a node boots uses these configuration files to create a number of slice pool RSpecs , and also identifies the slice creation service (e.g., plc.scs ) entrusted to create 26
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slices on the node (see Section 4.5). Only a single privileged VM belonging to the owner is allowed to initialized a slice creation service in this way.
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