公开(公告)号：US20020146130A1

公开(公告)日：2002-10-10

申请号：US10099589

申请日：2002-03-13

Applicant: STMicroelectronics Limited

Inventor： Andrew R. Dellow

IPC: H04L009/00

CPC classification number: H04N21/462 ,  H04N5/76 ,  H04N5/913 ,  H04N21/4334 ,  H04N21/434 ,  H04N21/4408 ,  H04N2005/91364

Abstract: A device for locating a DES key value that corresponds to a packet identification (PID) contained at a variable possible location which comprises part only of a 32-bit packet header. A table stored in memory contains for each DES key: (i) a packet header having 32 bits with a PID of either 12, 9 or 8 bits contained at a defined location and with zero values elsewhere, and (ii) a mask value also having 32 bits with ones contained at the said defined location of the PID and zeros elsewhere. The table is divided into regions for respective packet format types. An incoming packet header at an input is combined with a first one of the mask values from the table to provide a combined value that consists of the value held in the input packet header at the defined location and zeros elsewhere. This combined value is compared with the corresponding packet header stored in the table. When they are not equal, the combining and comparison is repeated for the next row of the table. When they are equal, the corresponding DES key value is read from the table and provided as an output. The system can cope with variable PID formats within the packet header without alteration to the hardware but merely with re-programming of the table contents.

Abstract translation: 用于定位对应于包含在可变可能位置的分组标识（PID）的DES密钥值的设备，该可变位置仅包括32位分组报头的一部分。 存储在存储器中的表包含每个DES密钥：（i）具有32位的分组报头，其中包含在定义的位置处的12,9或8位的PID，并且在其他地方具有零值，以及（ii）掩码值 具有32位，其中包含在PID的所述定义的位置处，并且其他地方具有零。 该表被分成用于相应分组格式类型的区域。 在输入处的输入分组报头与表中的第一个掩码值组合，以提供组合值，该组合值由保存在定义位置的输入分组报头中的值和其他地方的零组成。 将该组合值与存储在表中的相应分组报头进行比较。 当它们不相等时，对于表的下一行重复组合和比较。 当它们相等时，从表中读取相应的DES密钥值作为输出。 该系统可以处理数据包头中的可变PID格式，而不会改变硬件，但只能对表内容进行重新编程。