Method and apparatus for constructing a set-top box to protect cryptographic capabilities

Abstract

A construction arrangement for a small set-top box to protect cryptographic capabilities and prevent a digital program in clear from being able to be tapped as required by Digital Rights Management protocols. A first layer of sheet metal capable of blocking X-rays, is formed as a shallow pan to hold a set of printed circuit boards. A second layer has a thin epoxy based printed circuit material. A third layer has a printed circuit board with integrated components placed on top of the second layer. A fourth layer has a three layer thin printed circuit board with a first and second metallic layer and holes for large components, such as electrolytic capacitors. A black liquid thermosetting epoxy fills the interstices between the sheet metal layer and the second layer, and between the second layer and the third layer, and between the third layer and the fourth layer, thereby preventing access to exposed circuit trace carrying digital signals in the clear. A connection from the first metallic layer of the fourth printed circuit material layer to a sending circuit and a connection from the second metallic layer so that a short between these two layers sets off an indicator circuit that an attempt is made to enter the protected area.

1 - 28 . (canceled)  
   
   
       29 . A construction arrangement for a small set-top unit to protect cryptographic capabilities and prevent a digital program in clear from being able to be tapped as required by Digital Rights Management protocols, comprising: 
 a first layer of sheet metal capable of blocking X-rays, formed as a shallow pan to hold a set of printed circuit boards;    a second layer having a thin epoxy based printed circuit material;    a third layer having a printed circuit board with integrated components placed on top of the second layer;    a fourth layer having a three layer thin printed circuit board with a first and second metallic layer and holes for large components, such as electrolytic capacitors;    a black liquid thermosetting epoxy filling the interstices between the sheet metal layer and the second layer, and between the second layer and the third layer, and between the third layer and the fourth layer, thereby preventing access to exposed circuit trace carrying digital signals in the clear; and    a connection from the first metallic layer of the fourth printed circuit material layer to a sending circuit and a connection from the second metallic layer so that a short between these two layers sets off an indicator circuit that an attempt is made to enter the protected area.    
   
   
       30 . The construction arrangement for a small set-top unit as set forth in  claim 29 , further comprising: 
 a tamper detector having a sensor wire running along sides of chips containing sensitive information, said sensor wire including four wires, A, B, C, D, twisted together, with a far-end of the four wires terminating A and B in a first short circuit, and separately, C and D in a second short circuit; and    a four-wire connector terminating a near end of the four wires.    
   
   
       31 . The construction arrangement for a small set-top unit as set forth in  claim 29 , further comprising: 
 circuitry for detecting the first short circuit between the A and B wires, and the second short circuit between the C and D wires, for when the first short circuit or the second short circuit become an open circuit.    
   
   
       32 . The construction arrangement for a small set-top unit as set forth in  claim 29 , further comprising: 
 circuitry for detecting any cuts in the A and B wires, or in the C and D wires.    
   
   
       33 - 34 . (canceled)  
   
   
       35 . A method for constructing a small set-top unit to protect cryptographic capabilities and prevent a digital program in clear from being able to be tapped, comprising the steps of: 
 constructing a first layer of sheet metal capable of blocking X-rays, formed as a shallow pan to hold a set of printed circuit boards;    making a second layer having a thin epoxy based printed circuit material;    making a third layer having a printed circuit board with integrated components placed on top of the second layer;    a fourth layer having a three layer thin printed circuit board with a first and second metallic layer and holes for large components, such as electrolytic capacitors;    filling, with a liquid thermosetting epoxy, the interstices between the sheet metal layer and the second layer, and between the second layer and the third layer, and between the third layer and the fourth layer, thereby preventing access to exposed circuit trace carrying digital signals in the clear; and    attaching a connection from the first metallic layer of the fourth printed circuit material layer to a sending circuit and a connection from the second metallic layer so that a short between these two layers sets off an indicator circuit that an attempt is made to enter the protected area.    
   
   
       36 . The method for constructing a small set-top unit as set forth in  claim 35 , further comprising the steps of: 
 installing a tamper detector having a sensor wire running along sides of chips containing sensitive information, said sensor wire including four wires, A, B, C, D, twisted together, with a far-end of the four wires terminating A and B in a first short circuit, and separately, C and D in a second short circuit; and    attaching a four-wire connector terminating a near end of the four wires.    
   
   
       37 . The method for constructing a small set-top unit as set forth in  claim 35 , further comprising the steps of: 
 adding circuitry for detecting the first short circuit between the A and B wires, and the second short circuit between the C and D wwires, for when the first short circuitor the second short circuit become an open circuit.    
   
   
       38 . The method for constructing a small set-top unit as set forth in  claim 35 , further comprising the steps of: 
 adding circuitry for detecting any cuts in the A and B wires, or in the C and D wires.