Des/3Des Operation - Samsung S3C2501X User Manual

S3C2501X DES/3DES

8.4 DES/3DES OPERATION

The 64-bit data to be encoded should be written to DESINFIFO of DES/3DES block by CPU or DMA. When the
data conversion is completed, the Valid DESOUTFIFO bit in DESSTA is set to 1 and the CPU/DMA can read the
encrypted data from the DESOUTFIFO.
The DESINFIFO and DESOUTFIFO consists of eight 32 bit registers that are used for data storage. The
DESINFIFO has two data request options for data transmission, which is controlled by DESCON[7]. When the
DESCON[7] is set to "0", the Available DESINFIFO status means that DESINFIFO is empty for 4 word (If is
recommended, when DMA mode is selected). When the DESCON[7] is set to "1", the Available DESINFIFO
status means that DESINFIFO is empty for 2 word. Similarly, the DESOUTFIFO has two interrupt options for
data receiving, which is controlled by DESCON[7]. When the DESCON[7] is set to "0", the Valid DESOUTFIFO
status means that DESOUTFIFO has at least 4 word valid data (If is recommended, when DMA mode is
selected). When the DESCON[7] is set to "1", the Valid DESOUTFIFO status means that DESOUTFIFO has at
least 2 word valid data. When the Available DESINFIFO or Valid DESOUTFIFO request signal (interrupt or DMA
signal) is generated, the CPU or DMA can write or read data to/from the DESIN/OUTFIFO.
Software can use DES or 3DES according to applications, which is controlled by DESCON[5]. When the
DESCON[5] is set to "0" (the DES algorithm is used), the key1 value is used and the key2 and the key3 are
ignored. When the DESCON[5] is set to "1" (the 3DES algorithm is used), the Key1, key2 and key3 value are
used. The 3DES algorithm can select the number of keys (2 keys or 3 keys). It must be noticed that when the
3DES with 2 keys (not 3 keys) is selected, the key value of the key1 register and the key3 register must be the
same.
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