Note that this used to be called genrandom, until I found there was already a fairly useless standard linux utility called genrandom.
So djenrandom became the name.

This program generates random data with known controlled statistical properties. Its primary reason for existing is
to provide test data for calibrating and validating random number testing algorithms.

It implements a number of models, selected with the -m <model> option.

Pure : Uniform random data.
SUMS : Step Update Metastable Source. This models a step update metastable entropy source of the type used in Intel CPUs.
Biased : This model allows the probability of a 1 or 0 to be controlled.
Correlated : This model allows the serial correlation coefficient to be controlled.
Normal : This model generates Normal (or Gaussian) distributed data and outputs as floating point values.
SinBias : This model has a sinusoidally varying bias.
Markov 2 Parameter : This implements a two state model. States 1 and 0, which output 1 and 0 respectively. Two parameters
                     give the probability of transitioning from 1 to 0 and from 0 to 1. This model allows both
                     bias a serial correlation to be modelled in the same data series.
Markov Sigmoid : This generates bits by walking along a finite Markov chain with transition probabilities set
                     according to a chosen sigmoid curve. Moving left generates 0, moving right generates 1.
                     This enables both bias and serial correlation to be modelled in the same data series.
File : This reads data from a file and re-outputs it.

This program generates random data in 1KiByte blocks. The number of blocks is controlled by the -k <blocks> option.
Data is output in either hex or binary, using the -b flag.
The data is the same every time, unless you seed the generator from /dev/random using the -s option.
There are a variety of models

Usage: djrandom [-bsvhn] [-x <bits>] [-y <bits>] [-z <bits>] [-c <generate length>]
       [-m <|pure(default)|sums|biased|correlated|normal|sinbias|markov_2_param|file>] [-l <left_stepsize>]

       [-r <right_stepsize>] [--stepnoise=<noise on step>] [--bias=<bias>]
       [--correlation=<correlation>] [--mean=<normal mean>] [--variance=<normal variance>]
       [--pcg_state_16=<16|32|64>] [--pcg_generator=<LCG|MCG>] [--pcg_of=<XSH_RS|XSH|RR]
       [--sinbias_offset=<0.0 to 1.0>] [--sinbias_amplitude=<0.0 to 1.0>] [--sinbias_period=<samples per cycle>]
       [--p10=<probability of 10 transition] [--p01=<probability of 01 transition>]
       [--states=<integer of number of states in the markov chain>]
       [--sigmoid=<flat|linear|sums|logistic|tanh|atan|gudermann|erf|algebraic]
       [--min_range=<float less than max_range>][--max_range=<float greater than min_range>]
       [-o <output_filename>] [-j <j filename>] [-i <input filename>] [-f <hex|binary|01>]
       [-J <json_filename>] [-Y <yaml_filename>]
       [--bpb=<binary bits per byte>]
       [-k <1K_Blocks>] [-w [1..256]]
       [-D <deterministic seed string>]

Generate random bits with configurable non-uniformities.
  Author: David Johnston, dj@deadhat.com

  -m, --model=<pure(default)|sums|biased|correlated|lcg|pcg|xorshift|normal|file>   Select random source model

Step Update Metastable Source model (-m sums) Options

  -l, --left=<left_stepsize>     stepsize when moving left as a fraction of sigma_m.
  -r, --right=<right_stepsize>   stepsize when moving right as a fraction of sigma_m.
  --stepnoise=<noise on step>    variance of the noise on stepsize. e.g. 0.00001.

Biased model (-m biased) Options

  --bias=<bias>                  bias as a number between 0.0 and 1.0. Only for biased or markov model

Correlated model (-m correlated) Options

  --correlation=<correlation>    correlation with previous bit as a number between -1.0 and 1.0. Only for correlation or markov model

Sinusoidally Varying Bias model (-m sinbias) Options

  --sinbias_amplitude=<0.0 to 1.0>     Amplitude of the variation of the bias between 0.0 and 1.0. Only for sinbias model
  --sinbias_offset=<0.0 to 1.0>        Midpoint Offset of the varying bias between 0.0 and 1.0. Only for sinbias model
  --sinbias_period=<samples per cycle> Number of samples for a full cycle of the sinusoidally varying bias. Only for sinbias model

Two Parameter Markov model (-m markov_2_param) Options

  --fast                    Use a fast version on the generator.
         and one set of:
  --p10=<0.0 to 1.0>        The probability of a 1 following a 0, default 0.5
  --p01=<0.0 to 1.0>        The probability of a 0 following a 1, default 0.5
         or
  --bias=<0.0 to 1.0>               The ones probability, default 0.5
  --correlation=<-1.0 to 1.0>       The serial correlation coefficient, default 0.0
         or
  --entropy=<0.0 to 1.0>    The per bit entropy, default 1.0
  --bitwidth=<3 to 64>      The number of bits per symbol

Sigmoid Markov model (-m markov_sigmoid) Options

  --states=<n>              The number of states in the Markov Chain
  --sigmoid=<curve>         Curve name, one of: flat, linear, sums, logistic, tah, atan, gudermann, erf or algebraic, default linear
  --min_range=<float>               The start of the range of the curve. Usually between -5.0 and -2.0
  --max_range=<float>               The end of the range of the curve. Usually between 2.0 and 5.0

Normal model (-m normal) Options

  --mean=<normal mean>           mean of the normally distributed data. Only for normal model
  --variance=<normal variance>   variance of the normally distributed data

Linear Congruential Generator model (-m lcg) Options

  --lcg_a=<LCG multipler term>  Positive integer less than lcg_m
  --lcg_c=<LCG additive term>   Positive integer less than lcg_m
  --lcg_m=<LCG modulo term>     Positive integer defining size of the group
  --lcg_truncate=<lower bits to truncate>     Positive integer
  --lcg_outbits=<Number of bits per output>     Positive integer

Permuted Congruential Generator model (-m pcg) Options

  --pcg_state_size=<state size of PCG>  16 ,32 or 64
  --pcg_generator=<Generator Algorithm> MCG or LCG
  --pcg_of=<Output Function>            XSH_RS or XSH_RR

XorShift model (-m xorshift) Options

  --xorshift_size=[state size of xorshift]  32 or 128

General Options

  -x, --xor=<bits>               XOR 'bits' of entropy together for each output bit
  -y, --xmin=<bits>              Provides the start of a range of XOR ratios to be chosen at random per sample
  -z, --xmax=<bits>              Provides the end of a range of XOR ratios to be chosen at random per sample
  -s, --seed                     Nondeterministically seed the internal RNG with /dev/random
  -D, --detseed <seed string>    Deterministically seed the internal RNG with the given string
  -n, --noaesni                  Don't use AESNI instruction.
  -c, --cmax=<generate length>   number of PRNG generates before a reseed
  -v, --verbose                  output the parameters

File Options

  -o <output_filename>             output file
  -j, --jfile=<j filename>         filename to push source model internal state to
  -i, --infile=<input filename>    filename of entropy file for file model
  -f, --informat=<hex|binary|01>   Format of input file. hex=Ascii hex(default), 4 bit per hex character. binary=raw binary. 01=ascii binary. Non valid characters are ignored
  -J, --json=<JSON filename>       filename to output JSON information of the data to
  -Y, --yaml=<YAML filename>       filename to output YAML information of the data to
  -k, --blocks=<1K_Blocks>         Size of output in kilobytes

Output Format Options

  -b, --binary                output in raw binary format
  --bpb                       Number of bits per byte to output in binary output mode. Default 8.
  -w, --width=[1...256]       Byte per line of output

The most important option of all

  -h, --help                     print this help and exit

More Details on the models
-------------
Pure : The data produced from the Pure model is indistiguishable from uniform random bits where each bit is independent
       and has a 50% probability of being 1. It is generated from a variant of a CTR_DRBG with a couple of extra AES
       stages thrown in for fun.
       
SUMS : Step Update Metastable Source. This models a dual differential feeback cross coupled latch, as used in the
       Intel DRNG Entropy Source that feeds the RdRand and RdSeed instructions. It has a control variable t, which
       moved left or right based on evaluating a probability of moving away from the center. The curve is defined
       P = 0.5 * exp(-0.5 * t*t). This is computed with floating point arithmetic.
       Options are in the model to vary the left and right step sizes and to add noise to the step sizes.
       
Biased : This generates bits according to a given probabilty (bias) that the bit is 1.

Correlated : This model generates data with 50% bias and the given serial correlation coefficient.
             The probability of a bit being the same as the previous bit is computed from the SCC.
             P(a=b) = (1+scc)/2. This relationship only holds for unbiased bits.
             
Normal : This model generates Normal (or Gaussian) distributed data and outputs as floating point values.
         The algorithm to compute normal variates uses the Marsargalia Polar Method.
         
SinBias : This model has a sinusoidally varying bias. This is one of the models used by NIST in evaluating
          the SP800-90B Non-IID entropy lower bound tests. The frequency and amplitude of the sinuoid can
          can be controlled.
          
Markov 2 Parameter : This implements a two state model. States 1 and 0, which output 1 and 0 respectively. Two parameters
                     give the probability of transitioning from 1 to 0 and from 0 to 1. This model allows both
                     bias a serial correlation to be modelled in the same data series.
                     A three way relationship exists between the P01,P10 markov parameters, the SCC and mean of the
                     generated data and the entropy of the generated data. Allowing data with know SCC, mean and 
                     entropy to be generated. This is useful for testing entropy estimation algorithms.
                     One of the transition parameters, the SCC and mean or the entropy can be given.
                     If the entropy is given, then there is an infinite set of P01,P10 pairs that generate that
                     entropy level. They exist on a closed curve on the P01,P10 plane. The program will pick
                     one at random.
                     
Markov Sigmoid : This generates bits by walking along a finite Markov chain with transition probabilities set
                 according to a chosen sigmoid curve. Moving left generates 0, moving right generates 1.
                 This is similar to the SUMS model, except it is a finite state model, not a floating point
                 model. But choosing a range and curve appropriately, it is easy to model the feedback
                 curve in a feedback controlled entropy source.
                 A paper by Rachael Parker (DOI: 10.1109/IVSW.2017.8031540) includes proof that the occupancy
                 of the Markov states follows a normal distribution for any sigmoid. From this the average min
                 entropy of a group of bits from the source can be computed from the weighted average of the
                 min entropyies of bits from individual states.
                 The curves are
                 Flat           : P(move_left | x) = 0.5
                 Linear         : P(move_left | x) = x
                 algebraic      : P(move_left | x) = x/sqrt(1.0+(x*x))
                 atan           : P(move_left | x) = arctan(x)
                 tanh           : P(move_left | x) = hyperbolic_tangent(x)
                 erf            : P(move_left | x) = erf(x)
                 gudermann      : P(move_left | x) = 2.0*arctan(hyperbolic_tangent(x/2))
                 logistic       : P(move_left | x) = 1.0/(1.0+exp(-x))
                 
                 The range gives the bounds on the chosen curve. The algorithm scales the vertical position of the curve
                 to vary between -1 and +1, so that the curve intersects the 0.5 region. 
                 
                 
                 
File  : This reads a given file and outputs the data. This is useful for format conversion. It provides
        flexible input and output formats.