Description
The SS7 security gateway Encryption Algorithm identifier (SEA) is a specific parameter defined within the 3GPP Network Domain Security (NDS) framework, particularly for securing Signalling System No. 7 (SS7) based signalling. NDS/IP provides security for IP-based control plane traffic between network domains (e.g., between two different operators' networks or between different security domains within an operator's network). Security Gateways (SEGs) are the entities that implement the NDS/IP security functions, primarily IPsec.
When two SEGs establish a secure IPsec tunnel to protect signalling traffic (which may be SS7-over-IP, like SIGTRAN, or Diameter/SIP), they must negotiate the security associations (SAs) to be used. This negotiation includes selecting specific cryptographic algorithms for integrity protection and confidentiality (encryption). The SEA is the identifier used to specify *which* encryption algorithm has been agreed upon for use within that secure tunnel. It is part of the security association data that must be consistently configured and recognized by both peer SEGs to ensure interoperability and successful decryption of traffic.
The value of the SEA corresponds to a specific encryption algorithm defined in the relevant 3GPP security specification (TS 33.204). For example, it might point to algorithms like AES-CBC or 3DES. The SEA, along with other identifiers for integrity algorithms (like the SPI - Security Parameter Index, though SPI is more generic), allows the SEG to correctly process incoming protected packets by applying the correct decryption cipher. Its use is critical in a multi-vendor environment or where network operators may support a suite of algorithms with different strengths, allowing for a clear and unambiguous agreement on the algorithm to be used for a particular connection.
Purpose & Motivation
The SEA exists to solve the problem of algorithm negotiation and identification in a standardized, interoperable manner for securing SS7 signalling over IP networks. As core networks evolved from traditional TDM-based SS7 to IP-based transport (using SIGTRAN), the signalling links became vulnerable to IP-based attacks like eavesdropping and message modification. The NDS/IP framework was created to apply IPsec protection to this traffic.
A key challenge in any IPsec deployment is ensuring that both ends of a security association use the same cryptographic algorithms. Without a standardized identifier, different vendors or network configurations might refer to the same algorithm by different names or parameters, leading to connection failures. The SEA provides a specific, agreed-upon token within the 3GPP context for SS7 security gateways. It addresses the limitation of ad-hoc or proprietary algorithm selection mechanisms, ensuring that when a SEG in one network domain establishes a tunnel with a SEG in another domain, they can unambiguously identify the encryption algorithm to be used, enabling successful secure communication and maintaining the confidentiality of the signalling messages traversing the inter-operator interface.
Key Features
- Uniquely identifies the encryption algorithm for an IPsec security association between SEGs.
- Defined within the 3GPP NDS/IP framework (TS 33.204).
- Essential for interoperability between multi-vendor Security Gateways.
- Used in the context of securing SS7-based signalling over IP networks (SIGTRAN).
- Part of the negotiated or pre-configured security association parameters.
- Ensures consistent decryption processing on the receiving SEG.
Evolution Across Releases
Introduced with the enhancement of the NDS/IP specifications to more explicitly cover the security of SS7 signalling. Defined the SEA as a specific parameter for algorithm identification in the context of Security Gateway (SEG) communications, formalizing the method for agreeing upon encryption algorithms for protecting inter-domain signalling links in an all-IP core network.
Defining Specifications
| Specification | Title |
|---|---|
| TS 33.204 | 3GPP TR 33.204 |