Datasheet

■ DMA context in - Request a new context (DES0 Cin)
■ DMA data in - Request input data (DES0 Din)
■ DMA data out - Request output data read (DES0 Dout)
14.2.2 Interrupt Control
There is one interrupt for the DES that is sent to the interrupt controller. This interrupt is an OR of
the enabled interrupt bits in the DES Interrupt Status (DES_IRQSTATUS) register. These bits are
enabled through the DES Interrupt Enable (DES_IRQENABLE) register. The following events can
generate an interrupt bit to be set in the DES_IRQSTATUS register. These are:
■ New context input required
■ Data input required
■ Data output ready
14.2.3 Register Interface
The Register Interface block performs all address decoding and control; however, not all registers
are available in this block. The context and data input registers are in the DES engine.
14.2.4 DES Engine
The DES buffered engine consists of the following major functional blocks:
■ Cipher core: the DES algorithm
■ Mode control FSM: manages the data flow to and from the DES buffered engine and starts each
encrypt/decrypt operation
■ DES feedback mode block: the logic that implements the various feedback modes supported by
the DES buffered engine
14.2.4.1 Mode Control FSM
The Mode control FSM manages the data flow to and from the DES engine. This block also sends
a start pulse to the encrypt/decrypt core and triggers the core to use the new mode keys when a
new context is needed. This module also controls the 3DES operation, such that the DES core
module is triggered three times (with different keys) before the result data becomes available.
14.2.4.2 DES Feedback Mode Block
The DES feedback mode block buffers the input and output blocks and contains all logic to implement
the 3DES and various feedback modes. See the FIPS-81 document for details on the ECB, CBC,
and CFB modes of operation.
By itself, the DES cipher core outputs data compliant for ECB encryption. However, most applications
use DES with feedback. Feedback provides additional security by randomizing repeated patterns
in the plain text, which could otherwise be exploited to attack the cipher text. The DES buffered
engine supports ECB, CBC, and CFB modes of operations for the DES and 3DES algorithm.
3DES mode performs the DES algorithm three times on a single block and uses a different key for
each invocation of the DES algorithm, greatly increasing security of the cipher text but at the cost
December 13, 20131040
Texas Instruments-Advance Information
Data Encryption Standard Accelerator (DES)