Dvb scrambling control bitstamps
The EMMs are specific to each subscriber , as identified by the smart card in his receiver, or to groups of subscribers, and are issued much less frequently than ECMs, usually at monthly intervals. This being apparently not sufficient to prevent unauthorized viewing, TPS has lowered this interval down to about 12 minutes.
This can be different for every provider, BSkyB uses a term of 6 weeks. The contents of ECMs and EMMs are not standardized and as such they depend on the conditional access system being used.
The control word can be transmitted through different ECMs at once. This allows the use of several conditional access systems at the same time, a DVB feature called simulcrypt , which saves bandwidth and encourages multiplex operators to cooperate. Due to the common usage of CA in DVB systems, many tools to aid in or even directly circumvent encryption exist.
CAM emulators and multiple-format CAMs exist which can either read several card formats or even directly decrypt a compromised encryption scheme. A large proportion of the systems currently in use for DVB encryption have been opened to full decryption at some point, including Nagravision, Conax, Viaccess, Mediaguard v1 as well as the first version of VideoGuard. In Canadian and United States cable systems , the standard for conditional access is provided with CableCARDs whose specification was developed by the cable company consortium CableLabs.
Cable companies in the US are required by the Federal Communications Commission to support CableCARDs; standards now exist for two way communication M-card but satellite television has its own standards. Next generation approaches in the United States eschew such physical cards and employ schemes using downloadable software for conditional access such as DCAS.
The main appeal of such approaches is that the access control may be upgraded dynamically in response to security breaches without requiring expensive exchanges of physical conditional-access modules. Another appeal is that it may be inexpensively incorporated into non-traditional media display devices such as portable media players. From Wikipedia, the free encyclopedia.
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The examples and perspective in this article may not represent a worldwide view of the subject. You may improve this article , discuss the issue on the talk page , or create a new article , as appropriate. While the CSA algorithm uses bit keys, most of the time, only 48 bits of the key are unknown, since bytes 3 and 7 are used as parity bytes in CA systems, and may be easily recalculated. This opens up for possible known plaintext attacks when combined with knowledge of the underlying plaintext structure.
For instance, as the first three bytes of the PES header is known to always be 0x, it would be possible to launch a brute force attack. Such an attack would reveal millions of possible keys, but still few enough to make it practical to attempt decryption of other parts of the data with the same key in a second pass to recover the true key. However, 48 bits, even if small by today's standards, is a significant amount of keyspace to search through.
For most practical applications, one would want to break the key faster than it is changed, and as the key changes at a minimum of every seconds, this would require scanning through on average at least half the keyspace in that period of time.
Furthermore, even if dedicated hardware or FPGA implementations made it possible to test the required 2. Furthermore, the parity bytes could be replaced by real key bytes, increasing the keyspace to 64 bits, which is 65, times as large. By noting that MPEG-2 padding frequently requires long series of zeroes, leading to entire byte cells being encrypted with zeroes only, it is possible to build up a rainbow table recovering the key from such a known-zero block.
A block would be known to be zero if two blocks with the same ciphertext were found, since presumably both would be zero blocks. The attack described would require about 7. However, the attack is only effective when such all-zero padding blocks are present i.
Note that this differs from the brute-force attacks above in that the plain-text contents of the entire cell is known before the attack, not just parts of a block; it is this that enables the ahead-of-time computation of the rainbow table.
In , a fault attack  was published on the block cipher. The basic idea was to introduce a few deliberate faults in the intermediate calculations, making it possible to deduce the last eight round keys. From this, the final key can be computed. While very few faults are needed on average two or three per round key recovered , fault attacks are usually impractical to carry out, in that it requires the ability to change bits at will inside the hardware of a decoder that already has the key in question.
From Wikipedia, the free encyclopedia. Broadcast encryption and digital rights management. Card sharing FTA Pirate decryption. See also free-to-view and pay television. Retrieved from " https: Cryptographic algorithms Digital Video Broadcasting. Views Read Edit View history.