# US 8,544,077 B2 · Internet protocol telephony security architecture

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- Number: US 8,544,077 B2
- Document ID: US8544077B2
- Status: Granted
- Kind: B2
- Application number: 12/490,124
- Filed: 2009-06-23
- Published: 2009-12-31
- Granted: 2013-09-24
- Earliest claimed: 1999-04-09
- Assignees: Motorola Mobility LLC
- Applicants: Eric J. Sprunk; Paul Moroney; Alexander Medvinsky; Steven E. Anderson; Jonathan A. Fellows
- Inventors: Eric J. Sprunk; Paul Moroney; Alexander Medvinsky; Steven E. Anderson; Jonathan A. Fellows
- Web page: https://patentgrep.com/patent/US8544077B2

## CPC

- G06F 21/606: {by securing the transmission between two devices or processes}
- H04L 9/083: {involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]}
- H04L 9/0841: {involving Diffie-Hellman or related key agreement protocols}
- H04L 9/3213: {using tickets or tokens, e.g. Kerberos (network architectures or network communication protocols for entities authentication using tickets in a packet data network H04L63/0807)}
- H04L 9/3263: {involving certificates, e.g. public key certificate [PKC] or attribute certificate [AC]; Public key infrastructure [PKI] arrangements (network architectures or network communication protocols for supporting authentication of entities using certificates in a packet data network H04L63/0823)}
- H04L 63/0435: {wherein the sending and receiving network entities apply symmetric encryption, i.e. same key used for encryption and decryption (cryptographic mechanisms or cryptographic arrangements for symmetric key encryption H04L9/06)}
- H04L 63/0442: {wherein the sending and receiving network entities apply asymmetric encryption, i.e. different keys for encryption and decryption (cryptographic mechanisms or cryptographic arrangements for public-key encryption H04L9/30)}
- H04L 63/061: {for key exchange, e.g. in peer-to-peer networks (cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838)}
- H04L 63/062: {for key distribution, e.g. centrally by trusted party (cryptographic mechanisms or cryptographic arrangements for key distribution involving a central third party H04L9/0819)}
- H04L 63/0807: {using tickets, e.g. Kerberos (cryptographic mechanisms or cryptographic arrangements for entity authentication using tickets or tokens H04L9/3213)}
- H04L 63/12: {Applying verification of the received information (cryptographic mechanisms or cryptographic arrangements for data integrity or data verification H04L9/32)}
- H04L 65/1043: Gateway controllers, e.g. media gateway control protocol [MGCP] controllers
- G06F 12/1408: {by using cryptography (for digital transmission H04L9/00)}
- G06F 2207/7219: Countermeasures against side channel or fault attacks
- G06F 2211/008: Public Key, Asymmetric Key, Asymmetric Encryption
- G06F 2221/2129: Authenticate client device independently of the user
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A secure Internet Protocol (IP) telephony system, apparatus, and methods are disclosed. Communications over an IP telephony system can be secured by securing communications to and from a Cable Telephony Adapter (CTA). The system can include one or more CTAs, network servers, servers configured as signaling controllers, key distribution centers (KDC), and can include gateways that couple the IP telephony system to a Public Switched Telephone Network (PSTN). Each CTA can be configured as secure hardware and can be configured with multiple encryption keys that are used to communicate signaling or bearer channel communications. The KDC can be configured to periodically distribute symmetric encryption keys to secure communications between devices that have been provisioned to operate in the system and signaling controllers. The secure devices, such as the CTA, can communicate with other secure devices by establishing signaling and bearer channels that are encrypted with session specific symmetric keys derived from a symmetric key distributed by a signaling controller.

## Claims

### Claim 1

A secure IP telephony system, the system comprising:
a Cable Telephony Adapter (CTA) coupled to an IP telephony network and comprising a public/private key pair and a public key certificate signed by a certificate authority;
a Key Distribution Center (KDC) coupled to the IP telephony network and configured to generate a ticket and session key to the CTA in response to a request from the CTA and distribute the session key to the CTA using public key encryption; and
a signaling controller coupled to the IP telephony network and configured to receive the ticket in a set up request from the CTA and generate and distribute a symmetric sub-key to the CTA in response to the set up request in a reply message, wherein both the call set up request and the reply message are encrypted using the session key,
wherein the ticket includes an identity of the CTA, an identity of the signaling controller, and an expiration time.

### Claim 2 (depends on 1)

The system of claim 1, wherein the CTA establishes a secure session with the signaling controller based on the sub-key.

### Claim 3 (depends on 1)

The system of claim 1, wherein the KDC is configured to distribute a Kerberos ticket to the CTA in a Kerberos exchange.

### Claim 4 (depends on 1)

The system of claim 1, wherein the signaling controller is further configured to generate an end to end sub-key and send it both to the CTA and to a destination device.

### Claim 5 (depends on 4)

The system of claim 4 wherein the CTA and the destination device derive at least one symmetric bearer traffic key from the end to end sub-key.

### Claim 6 (depends on 4)

The system of claim 4, wherein the destination device is associated with a remote signaling controller and wherein the signaling controller delivers the end to end sub-key to the destination device via the remote signaling controller.

### Claim 7 (depends on 4)

The system of claim 4 wherein the CTA and the destination device derive at least one symmetric signaling key from the end to end sub-key.

### Claim 8 (depends on 7)

The system of claim 7, wherein the at least one symmetric signaling key comprises: an Hash-based Message Authentication Code (HMAC) key; and a Data Encryption Standard (DES) key.

### Claim 9 (depends on 8)

The system of claim 8, wherein the HMAC key comprises a 160-bit Secure Hash Algorithm (SHA-1) HMAC key.

### Claim 10 (depends on 8)

The system of claim 8, wherein the DES key comprises a 168-bit 3 DES key.

### Claim 11 (depends on 7)

The system of claim 7, wherein the at least one symmetric bearer traffic key comprises at least one 3 DES key.

### Claim 12 (depends on 11)

The system of claim 11, wherein the at least one 3 DES key comprises a first 168-bit 3-key 3 DES key for encrypting a transmit direction and a second, distinct 168-bit 3-key 3 DES key for encrypting a receive direction.

### Claim 13 (depends on 1)

The system of claim 1, wherein the signaling controller is further configured to distribute an end to end sub-key to a destination device.

### Claim 14 (depends on 13)

The system of claim 13, wherein the CTA is configured to communicate with the destination device using symmetric encryption keys derived from the end to end sub-key.

### Claim 15 (depends on 13)

The system of claim 13, wherein the CTA is configured to communicate bearer channel traffic with the destination device using RTP packets encrypted with a at least one symmetric key derived from the end to end sub-key.

### Claim 16 (depends on 13)

The system of claim 13, wherein the CTA is configured to communicate encrypted signaling messages with the destination device using an IPsec ESP session with at least one symmetric key derived from the end to end sub-key.

### Claim 17 (depends on 13)

The system of claim 13, wherein the destination device comprises a remote CTA coupled to the IP telephony network.

### Claim 18 (depends on 13)

The system of claim 13, wherein the destination device comprises a Plain Old Telephone Service (POTS) gateway coupled to the IP telephony network.