| 摘要 |
For this reason, the present invention proposes to allow the development of a first security based on a first key towards a second security based on a second ke y, this operation being carried out in an environment unprotected by said open transmission, guaranteeing the same security level as if this operation was carried out locally in the place belonging to the system manager. This aim is achieved by a security updating method applied to the connecti on between a decoder and its security unit comprising a first matching key, sai d decoder being linked to a managing centre, this method having the following steps: .cndot. transmission in the decoders, of a shared public key and of an updating programme, .cndot. preparation at the managing centre and for each decoder, of a coded message, this message containing a new asymmetric public key coded by the first key of said decoder and by the secret shared key, .cndot. carrying out of the updating programme and extraction of the new asymmetric public message key thanks to the global public key and its first key, .cndot. storage of this new public key in the decoder.
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