Conditional Access Encryption Marker Verification
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Solution Overview
Problem
In conditional access systems, particularly in Pay-TV, it is challenging to synchronize encryption keys with data packets, leading to incorrect decryption and access issues due to the inability to include key change information within fixed-length data packets, resulting in frequent errors where a packet is decrypted with the wrong key.
Innovation Solution
The method involves encrypting data packets with alternating keys and padding values, creating marking blocks, and decrypting mixed blocks to verify correct key usage, ensuring that only the correct key decrypts a packet to include a marker, thereby preventing key confusion and ensuring access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data packets are encrypted with changing keys to improve security, then security level is improved, but the ability to synchronize decryption keys with data packets deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and inserting encrypted marker values into data packets during the encryption process. These markers are prepared in advance and embedded within the packet structure, allowing the receiver to verify key correctness without requiring complex synchronization mechanisms. The markers are computed before transmission using the same key that encrypts the packet content.
Solution Approach 2:
The patent introduces encrypted marker values as intermediaries between the encryption key and the decryption verification process. These markers serve as mediators that carry key-verification information within the packet itself, enabling the receiver to test multiple keys without external synchronization. The markers act as a bridge that links the cryptographic key to the packet content in a self-contained manner.
2Ease of manufacture
If fixed-length data packets are used to maintain packet structure, then packet formatting is simplified, but the ability to include key change information within packets deteriorates
Solution Approach 1:
The patent applies the nested doll principle by embedding encrypted marker values within the existing fixed-length packet structure. The markers are nested inside the packet as part of the encrypted content, utilizing the same space already allocated for data. This allows key verification information to be contained within the fixed-length packet without requiring additional space or changing the packet format.
Solution Approach 2:
The patent uses parameter changes by transforming the marker into an encrypted form that fits within the fixed packet structure. The marker is encrypted using the same key as the packet content, changing its parameter state from plain text to encrypted form. This allows the marker to be included within the fixed-length constraint while still carrying key verification information.
3Reliability
If decryption attempts are made with multiple keys to ensure correct key usage, then key verification capability is improved, but the frequency of random marker matches and access errors deteriorates
Solution Approach 1:
The patent applies asymmetry by using different marker positions for encryption and verification. The marker is encrypted at a specific position within the packet using the content key, but during verification, the receiver extracts and decrypts the marker separately and compares it against an independently computed reference marker. This asymmetric treatment of the marker prevents false matches that would occur with symmetric verification approaches.
Solution Approach 2:
The patent extracts the marker from the main packet content and handles it separately during verification. The receiver extracts the encrypted marker value from the packet, decrypts it independently using candidate keys, and compares it against a separately computed reference marker. This extraction and separate handling of the marker reduces the probability of random matches compared to verifying the entire packet content.
Data Source
AI summary
Example embodiments relate to an encryption and decryption method for a conditional access content, including (a) extracting a marker (Mc) from a data packet (DP); (b) creating a first marking block including the marker (Mc) and a second padding value (PAD2); (c) encrypting the first marking block with a second encryption key (K2); (d) encrypting a second encrypted marking value (MK2) of the first encrypted marking block; (e) creating a mixed marking block including the second encrypted marking value (MK2) a the first encrypted padding element (PADK1); (f) decrypting the mixed marking block a device of the first encryption key (K1), in order to obtain a decrypted mixed marking block; (g) extracting a predetermined part of the decrypted mixed marking block; (h) comparing the extracted part with a reference value (Mc; PDV2); and (i) if the comparison leads to an identity, determining a new set of encryption parameters different to the first set of encryption parameters and repeating steps b) to h) in which the second set of encryption parameters is replaced by the new second set of encryption parameters.