K60P100M100SF2RM Datasheet, PDF (794/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
33.4 Functional Description
The RNGB performs two functional operations, as described in Modes of Operation :
seed generation and random number generation. Theses operations are performed with
cooperation from the major functional blocks in the RNGB described below.
33.4.1 Pseudorandom Number Generator (PRNG)
The PRNG implements the NIST-approved PRNG described in the Digital Signature
Standard. The 160-bit output of the SHA-1 block is the next five words of random data.
The PRNG is designed to generate 2²⁰ words of random data before requiring reseeding,
using the TRNG only during the seeding/initialization process. The initial seed takes
approximately two million clock cycles. After this the RNGB can generate five 32-bit
words every 112 clock cycles. Reseeding takes place transparently through use of the
simultaneous reseed LFSRs. The entropy stored in this 128-bit LFSR and 128-bit shift
register is added directly into the XKEY structure via the RNGB XSEED generator
whenever reseeding is required.
33.4.2 True Random Number Generator (TRNG)
The TRNG is comprised of two entropy sources each providing a single bit of output.
Concatenated together, these two output bits are expected to provide one bit of entropy
every 100 clock cycles. In addition to generating entropy, the TRNG also performs
several statistical tests on its output. The pass/fail status of these tests are reflected in
RNG_ESR.
33.4.3 Resets
There are two ways to reset the RNGB: power-on/hardware reset and software reset. The
software reset is functionally equivalent to the power-on/hardware reset. The power-on/
hardware reset is asynchronous. Software reset is performed by setting the
RNG_CMD[SR] bit. These are summarized in the table below.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
794
Freescale Semiconductor, Inc.