Overview
The
supports the exchange of SIP signaling over Transport Layer Security (TLS), an IETF protocol for securing communications across an untrusted network. Normally, SIP packets travel in plain text over TCP or UDP connections. Secure SIP is a security measure that uses TLS, the successor to the Secure Sockets Layer (SSL) protocol. TLS operates just above the transport layer (Layer 4) and provides peer authentication, confidentiality and message integrity.
The
supports TLS versions 1.0, 1.1 and 1.2 with server-only authentication (in which only the server is authenticated at the TLS layer) and mutual authentication (in which both the TLS client and server are authenticated at the TLS layer). TLS is an effective measure to a number of threats including theft of service, disruption of service, compromise of confidentiality, and compromise of service integrity.
SIP over TLS may be independently configured on each hop between SIP devices. SIP transport type selection is typically configured via the IP Signaling Profile, and may also be provisioned on the SIP trunk group or identified via a DNS lookup.
Usage Scenarios and TLS Roles
The
uses SIP over TLS in several scenarios as illustrated in the figure below
.
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| 0 | Figure |
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| 1 | SIP over TLS Usage Scenarios |
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The table below describes the interrelationship between each of these scenarios, the TLS role (server or client/server), and the authentication requirements.
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| 0 | Table |
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| 1 | TLS Usage Scenarios |
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Usage Scenario | Usage Description | TLS Role | Authentication Requirements |
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Residential Access | Between a subscriber SIP User Agent (UA) and an SBC. | Server | Server-only authentication. This is intended for use in conjunction with authenticated SIP registration. A peer is blocked from using any services until a successful SIP registration is performed. A separate registrar is deployed to challenge and authenticate the registration; this may be a Sonus ASX or other device. The registrar should be configured to require authentication on the registration; however the does not check or enforce this. | Enterprise Access | Between an enterprise PBX and an SBC. | Server | Mutual TLS authentication for static (non-registering) IP PBX. Server-only Authentication for registering PBX. | Inter-Carrier Peering | Between a SIP proxy or Back-to-Back User Agent (B2B UA) belonging to another administrative domain and an SBC. | Client or Server | Mutual TLS authentication. | Intra-Carrier Peering | Between an SBC and a SIP proxy or a B2B UA belonging to the same administrative domain. | Client or Server | Mutual TLS authentication |
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Deployments may involve two or more of the above scenarios and include different transports (SIP over TLS, SIP over TCP, or SIP over UDP) simultaneously on separate legs of the same signaling path.
Cipher Suites
Cipher suites define a set of ciphers (algorithms used for encrypting data) which allows selection of an appropriate level of security. When a TLS connection is established, the client and server exchange information about which cipher suites they have in common. The following cipher suites are supported:
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| 0 | Table |
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| 1 | Supported Cipher Suites |
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| Authentication Mechanism | Public/Private Key Pair | Confidentiality Cipher and Mode | Integrity Cipher |
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RSA-WITH-NULL-SHA The integrity cipher used for the TLS Record protocol. | RSA | NULL | SHA-1 | RSA-WITH-3DES-EDE-CBC-SHA Authentication mechanism in the TLS Handshake protocol.
| RSA | 3DES-EDE-CBC | SHA-1 | RSA-WITH-AES-128-CBC-SHA (default) Confidentiality cipher and mode for the TLS Record protocol. | RSA | AES-128-CBC | SHA-1 | RSA-WITH-AES-128-CBC-SHA-256 Confidentiality cipher and mode for the TLS Record protocol with SHA-256 as the hash function. | RSA | AES-128-CBC | SHA-256 | RSA-WITH-AES-256-CBC-SHA Confidentiality cipher and mode for the TLS Record protocol with AES 256 encryption. | RSA | AES-256-CBC | SHA-1 | RSA-WITH-AES-256-CBC-SHA-256* Confidentiality cipher and mode for the TLS Record protocol with AES 256 encryption and SHA-256 as the hash function. | RSA | AES-256-CBC | SHA-256 | TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384** Confidentiality cipher and mode for TLS Recod with AES256 CBC and SHA384 as hash function. | ECDH-ECDSA | AES-256-CBC | SHA-384 | TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384** Confidentiality cipher and mode for TLS Recod with AES256 GCM and SHA384 as hash function. | ECDH-ECDSA | AES-256-GCM | SHA-384 | TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA Confidentiality cipher and mode for the TLS Record protocol using ECDHE (Elliptic Curve Diffie-Hellman key Exchange) with AES128 CBC and SHA as hash function. | ECDHE-RSA | AES-128-CBC | SHA-1 | TLS-ECDHE-RSA-WITH-AES-256-CBC-SHA-384* Confidentiality cipher and mode for the TLS Record protocol using ECDHE (Elliptic Curve Diffie-Hellman key Exchange) with AES256 CBC and SHA384 as hash function. | ECDHE-RSA | AES-256-CBC | SHA-384 |
* To use this cipher, TLS version 1.2 must be enabled in the TLS Profile. ** To use this cipher, TLS version 1.2 must be enabled in the TLS Profile and SSL certificates must be created using ECC keys. |
| Info |
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Terms used in this table: RSA – Authentication based on X.509 certificates using RSA public/private key pairs
3DES-EDE – Data Encryption Standard applied three times with Encrypt Decrypt Encrypt
AES-128 – Advanced Encryption Standard (128-bit key length)
CBC – Cipher Block Chaining
SHA – Secure Hash algorithm |
| Note |
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When fips-140-2 mode is enabled, do not use rsa-with-null-sha option. |
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The
and its peer devices use X.509 digital certificates to authenticate themselves for TLS. Local certificates in PKSC # 12 format (attesting to the identity of the
) and remote Certificate Authority (CA) certificates may be installed on the
in a common area (/opt/sonus/external/) where they are available to TLS.