Patent ID: 9544276
Date: 2017-01-10
CPC Classifications: H04L

Claim:
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.