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Lecture Notes in Computer Science 4917

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60 R. Chaves et al.<br />

the coprocessor architectural paradigm, allow<strong>in</strong>g the usage of reconfigurable custom<br />

designed hardware units. In this computational approach, the non critical part of the<br />

software code is executed on a General Purpose Processor (GPP), while the ma<strong>in</strong> DES<br />

algorithm, is executed on the Custom Comput<strong>in</strong>g Unit (CCU). The DES core is seen by<br />

the programmer <strong>in</strong> the same manner as a software implemented function. The decision<br />

where the function is executed is made at compile time. At microarchitectural level the<br />

arbiter, depicted <strong>in</strong> Figure 7, redirects each <strong>in</strong>struction either to the GPP (a PowerPC <strong>in</strong><br />

our case) or to the cryptographic units.<br />

64<br />

64<br />

Load<br />

Round<br />

MUX<br />

Address<br />

& Data<br />

Data<br />

KEY_IN<br />

MUX_C<br />

SHIFTER_C<br />

Current_KEY<br />

64<br />

PC-1<br />

24 24<br />

PC-2<br />

48<br />

MUX_D<br />

SHIFTER_D<br />

Fig. 6. DES key expansion<br />

Ma<strong>in</strong> Memory<br />

Memory<br />

selection<br />

Key<br />

expansion<br />

DES<br />

Instructions<br />

ARBITER<br />

Address<br />

Start<br />

/Stop<br />

32<br />

HALT<br />

Address<br />

& Data<br />

Control<br />

Unit<br />

DES core<br />

PowerPC<br />

Register<br />

File<br />

Address<br />

& Data<br />

32<br />

Load<br />

Round<br />

Fig. 7. Polymorphic processor <strong>in</strong>ternal structure<br />

XREG

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