DEVRANDOM

Arduino library to wrap a random generator in a stream

Description

The library implements a stream class that mimics the /dev/random device of a linux system. It can be used for testing with streams.

Interface

Constructor

DEVRANDOM() Constructor
DEVRANDOM(char * str) Constructor
DEVRANDOM(uint32_t val) Constructor
DEVRANDOM(float val) Constructor

Streeam interface

to read and to reseed the random generator.

available() There is always 1 next byte available
peek() will give you next byte
read() will give you next byte and generate a new one.
write() data will be used for reseeding the random number generator (RNG) (SW mode only, in HW mode and AN mode the seed is used to XOR the value, so it does have some effect);
flush() to keep the CI happy.

Random generator selection

useSW() use a software random number generator. This is the default. By default the build-in random number generator is used. This can be replaced by a RNG of your choice.
useHW(pin) use digitalRead to read 8 bits from a defined pin. One can build a hardware RNG that flips between 0 and 1 very rapidly and unpredictably. Connect this signal to the pin and it will be read and generate a random byte. The seed value from the write is used as an XOR byte.
useAR(pin) use the analogRead to read 8 bits This can be fed with an analog noise source. The seed value from the write is used as a XOR byte.
getMode() returns the source of randomness => 0=SW, 1=HW, 2=AR (see above).

As write() reseeds the RNG, printing to DEVRANDOM will also reseed the RNG. E.g. dr.println("Hello world"); would reseed it too.

Operation

See example sketches.

Example

As shown in the example one can use fscanf to read larger datatypes,

  DEVRANDOM dr;
  uint32_t x;
  fscanf((FILE*) &dr, "%lu", &x);
  Serial.println(x);

However float is not supported standard in the fscanf by UNO and strings (%s) generate garbage. So a password generator is a bit more difficult (and a good exercise).

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