Secured Packet

Description

In 3GPP security architecture, a Secured Packet is a fundamental concept for protecting application messages exchanged between network entities. It is defined as the information flow on top of which the level of required security has been applied. This means that an Application Message, which is the original data to be transmitted, is transformed with respect to a chosen Transport Layer and a chosen level of security into one or more Secured Packets. The transformation typically involves cryptographic operations such as encryption, integrity protection, and replay protection. The Transport Layer determines the mechanism for delivering the Secured Packet, such as SMS, HTTP, or IP. The level of security is selected based on the security policy and the sensitivity of the application data.

The Secured Packet concept is used in various 3GPP specifications, including TS 22.048 (Security mechanisms for the (U)SIM application toolkit), TS 23.048 (Security mechanisms for the (U)SIM application toolkit; Stage 2), and TS 31.114 (Application of the Secure Channel Protocol). These specifications define how Secured Packets are constructed and processed for over-the-air (OTA) communication with the (U)SIM card. For example, in OTA provisioning, the operator sends a Secured Packet containing commands to update the SIM card. The Secured Packet ensures confidentiality and integrity of the commands, preventing unauthorized access.

The architecture involves a Secured Packet Gateway (or similar entity) that applies security to outgoing messages and verifies incoming Secured Packets. The gateway uses keys and algorithms agreed upon with the (U)SIM. The Secured Packet format typically includes a header, payload, and security trailer (e.g., MAC, encryption). The transport layer may add its own headers. The receiving entity (e.g., the (U)SIM) processes the Secured Packet by verifying integrity, decrypting if necessary, and then extracting the original Application Message. If multiple Secured Packets are needed (e.g., due to size constraints), the original message is segmented and each segment is secured separately.

The Secured Packet concept is essential for ensuring end-to-end security in scenarios where the transport network is not trusted. It allows application-level security to be applied independently of the transport security, providing defense in depth. It also supports different security levels, from no security to high security, depending on the application's requirements. This flexibility is important for balancing security and performance. The definition has remained unchanged since Release 5, indicating its stability and continued relevance in 3GPP security standards.

Purpose & Motivation

The Secured Packet concept was created to provide a standardized way to secure application messages in 3GPP networks, particularly for communication with the (U)SIM card. Before its introduction, security mechanisms were often proprietary or ad-hoc, leading to interoperability issues and potential vulnerabilities. The Secured Packet provides a clear framework for applying security at the application layer, independent of the transport layer. This allows operators to securely provision and manage SIM cards over-the-air, even when the transport network (e.g., SMS) is not inherently secure. It also enables a consistent security approach across different applications and services, simplifying implementation and reducing the risk of security gaps.