The DLNA’s support for streaming of premium content within the home, announced at IBC and initially for Europe only, is a major milestone in the evolution of connected home services. The move might have come sooner, but DLNA was waiting for maturation of the key underlying technology, DTCP-IP (Digital Transmission Content Protection over IP) to ensure safe and yet transparent delivery of content over IP networks. DTCP itself evolved in the mid 1990s, developed by chip maker Intel in conjunction with four major CE (consumer electronics) companies, Hitachi, Panasonic, Sony and Toshiba.
Collectively known as 5C, these five companies appreciated early on the impending need for a protocol capable of protecting audio/video entertainment content from illegal copying, interception and tampering as it traverses digital interfaces, such as USB ports.
The extension to IP came later, as did the crucial support for mechanisms designed to prevent content from being transmitted from a device inside the home to another device somewhere else. This was a vital step in persuading major rights holders such as Hollywood studios that they can trust home networks for delivery of their valuable premium content.
Apart from satisfying content owners, there is another important reason for DLNA’s adoption of DTCP-IP for copy protection around the home, which is to enable consumers to exercise their digital rights to the full. To do this, DTCP-IP enables operators to enforce multi-level rights dependent on the content.
Until now consumer devices have displayed video via either analogue interfaces, or the digital HDMI (High Definition Multimedia Interface), which incorporates a copy protection mechanism developed by Intel called HDCP (High-bandwidth Digital Content Protection) precisely to prevent consumers copying or recording. This allows no rights beyond immediate display of the content.
DTCP-IP on the other hand allows consumers to copy and record content subject to permission from the operator or rights holder. The rights are specified in a licence issued by the Digital Transmission Licensing Administrator (DTLA), details of which can be obtained from its website. The idea is that the licence encodes rules into the content, so that, for example, free-to-air terrestrial broadcasts could be recorded and copied without any restriction. In the case of subscription channels, consumers may be allowed to record content for their own subsequent viewing, but not copy it for sending to friends. Then premium content such as movies or live sports purchased on demand or pay-per-view via a specific transaction would probably be fully protected against recording and copying.
This begs the question of how these rights are robustly enforced, given that DTCP-IP is a software-only mechanism, as a result of the decision by CE makers that it would be impractical and too expensive to enforce hardware protection on the whole constellation of CE devices since unnecessary incremental costs must be avoided. The idea then is that hardware protection is confined to the set top box or gateway linking the home network with external delivery network via the operator’s Conditional Access (CA) system. Such boxes may well have SoCs (System on Chips) incorporating security hardware blocks such as Cryptography Research’s Crypto Firewall.
But then, from the gateway or set top onwards through the home network, the DLNA platform will take over with the software based DTCP-IP, although this will operate in cooperation with the CA and DRM, enforcing whatever rights they specify. In order to provide robust security without hardware, the developers of DTCP-IP, spearheaded by Intel, have developed some clever tricks.
First, and most obviously, DTCP-IP requires the devices at each end of a link to validate each other’s DTLA licenses via a joint authentication procedure comprising a sequence of data swaps and key calculations. This is designed to prevent pirates from inserting a circumvention device that would record a copy protection data exchange or strip out the protection, since such a device would first have to be authenticated before any communication with it could take place.
Secondly the 5C consortium have implemented specific measures that act in combination to prevent a device in a home transmitting content, whether previously recorded or streamed, to any other device outside the home even next door, unless the rights allow this. One of these measures involves limiting how many routers any IP packet that is part of the protected video can traverse before being deleted, which itself is effective in preventing transmission outside the home. Another measure involves measuring the delay between source and destination before allowing video to be transmitted.
Between them, these measures enable the operator to determine whether a DTCP device is trying to communicate with another device in the same home, with a near neighbor’s, or a more remote one, and act accordingly depending on the rights. This is a significant advance in software-only security and is the reason DTCP-IP has been embraced by DLNA and welcomed so warmly by pay-TV operators, including BSkyB and Orange in Europe. However, the full response of major rights holders has yet to come, and will ultimately determine whether the industry has hit on the right content protection solution for the future digital home.
The DLNA has emerged as the universal standards body defining the overall platform for the digital home, embracing standards developed by others, including Universal Plug and Play (UPnP) for device discovery and the lower level physical networking standards such as MoCA, as well as DTCP-IP.
