| 摘要 |
A method for transmitting and receiving multimedia content having cryptoperiods scrambled by a control word includes a sender using an operating key and an encryption algorithm in a first virtual mother card to encrypt the control word to obtain a cryptogram, using a syntax constructor also in the first virtual mother card to generate an ECM that incorporates the cryptogram, and transmitting it to a terminal. The terminal receives the ECM and using a syntax analyzer contained in a first virtual daughter card associated with the mother card and uses it to locate a position of the cryptogram CW*t in the ECM. Using an operating key of a decryption algorithm in the daughter card, it then decrypts the cryptogram. Then, using the decrypted control word, it proceeds to descramble the cryptoperiod. Meanwhile, the sender occasionally changes the virtual mother card into a different virtual mother card. |
| 主权项 |
1. A method for transmitting and receiving a multimedia content, each cryptoperiod CPt of said multimedia content is scrambled by a respective control word CWt, said method comprising
using an operating key and executable code of an encryption algorithm contained in a first virtual mother card, encrypting, by a sender, said control word CWt to obtain a cryptogram CW*t, using executable code of a syntax constructor contained in said first virtual mother card, generating, by said sender, an entitlement control message that incorporates said cryptogram CW*t, and transmitting, by said sender, said entitlement control message to a terminal, at said terminal, receiving said entitlement control message, using executable code of a syntax analyzer contained in a first virtual daughter card associated with said first virtual mother card, locating a position of said cryptogram CW*t in said received entitlement control message, and using an operating key and a decryption algorithm contained in said first virtual daughter card, decrypting said cryptogram CW*t to obtain a decrypted control word CWt, using said decrypted control word CWt, descrambling a cryptoperiod CPt of said scrambled multimedia content, changing, by said sender, at a frequency selected to achieve a selected level of security, said first virtual mother card into a second virtual mother card used to encrypt a control word CWt+n to obtain a cryptogram CW*t+n of a following cryptoperiod CPt+n of said multimedia content, wherein changing, by said sender, said first virtual mother card comprises automatically changing said first virtual mother card at least once each two-hour period and wherein said second virtual mother card differs from said first virtual mother card by having a different operating key and a difference in at least one of executable code of an encryption algorithm thereof and executable code of a syntax constructor thereof, in response, selecting, by said terminal, a second virtual daughter card to be used to decrypt said cryptogram CW*t+n so as to obtain said control word CWt+n. |
