Implementation of a CSPRNG algorithm in C

[ribei...@gmail.com]

I need help to implement the algorithm of my own in C language.
Someone can help me ?

Here is the algorithm:

Melgo a csprng by Ribeiro Alvo 2017

Description

a,b,c,d and n as ( 16 bit )
i as ( 64 bit )
n = 2**16-1
a = Initialzed in [ 0 , n ]
b = Initialzed in [ 0 , n ]
c = Initialzed in [ 0 , n ]
d = 2**13
X[ from 0 to n ] = Initialzed with a 61 bit values


Key-scheduling algorithm

for i from 0 to n
a = 1 + [ a + c ] mod n
b = 1 + [ b + a ] mod n
c = 1 + [ c + b ] mod n
X[i] = X[i] + a * b * c * d + a
endfor

Pseudo-random generation algorithm

i = 0
while GeneratingOutput:

i = i + 1
X(a) = [X(a) + X(b)] mod 2**62
a = [a + c + i] mod [n + 1]
Output [X(a) + X(b)] mod 2**56
b = [b + a] mod [n + 1]
Output [X(b) + x(c)] mod 2**56
c = [c + b] mod [n + 1]
Output [X(c) + x(a)] mod 2**56

endwhile



Thank you

[red floyd]

On 10/5/2017 11:44 AM, ribei...@gmail.com wrote:
> I need help to implement the algorithm of my own in C language.
> Someone can help me ?

> [redacted]

You may have come to the wrong place. This is comp.lang.c++.
You may want to try comp.lang.c instead.

[ribei...@gmail.com]

Thanks
I'll do it
But if a C ++ version is possible, I would also appreciate it.

[Ben Bacarisse]

ribei...@gmail.com writes:

> I need help to implement the algorithm of my own in C language.

For C, I'd post in comp.lang.c. This group is for C++.

Since I've included C source, I've set the followup-to header to avoid a
language debate. If you reply, please honour that header.

> Someone can help me ?
>
> Here is the algorithm:
>
> Melgo a csprng by Ribeiro Alvo 2017
>
> Description
>
> a,b,c,d and n as ( 16 bit )
> i as ( 64 bit )
> n = 2**16-1
> a = Initialzed in [ 0 , n ]
> b = Initialzed in [ 0 , n ]
> c = Initialzed in [ 0 , n ]
> d = 2**13
> X[ from 0 to n ] = Initialzed with a 61 bit values

How are a, b, c and X initialised? Below, there's a hint you mean
62-bit values.

> Key-scheduling algorithm
>
> for i from 0 to n

Does i ever get to n? I.e. is the upper bound of the for inclusive or
not?

> a = 1 + [ a + c ] mod n
> b = 1 + [ b + a ] mod n
> c = 1 + [ c + b ] mod n

What do the []s mean here? Is it grouping the "mod n"? I.e.

a = 1 + ((a + c) mod n))

> X[i] = X[i] + a * b * c * d + a

Are the X[i] supposed to be reduced to being 61-bit (or 62-bit) values?
I'm guessing yes.

> endfor
>
> Pseudo-random generation algorithm
>
> i = 0
> while GeneratingOutput:
>
> i = i + 1
> X(a) = [X(a) + X(b)] mod 2**62
> a = [a + c + i] mod [n + 1]
> Output [X(a) + X(b)] mod 2**56
> b = [b + a] mod [n + 1]
> Output [X(b) + x(c)] mod 2**56
> c = [c + b] mod [n + 1]
> Output [X(c) + x(a)] mod 2**56
>
> endwhile

It would be much better to use consistent notation. Keep [] for
indexing and use () for arithmetic grouping.

It's not clear if the output refers to three separate outputs or of the
generator is to make one 168-bit number at a time. Since making three
separate 56-bit values is more interesting, that's the interpretation
I've chosen.

Here's a first draft. You need C99 or later.

#include <stdio.h>

unsigned long long csprng(void)
{
const unsigned d = 1 << 13;
const unsigned n = 0xFFFF;
const unsigned long long mask_62_bits = (1ull << 62) - 1;
const unsigned long long mask_56_bits = (1ull << 56) - 1;

static unsigned a, b, c;
static unsigned long long X[0x10000];

static int state = 0;
static unsigned long long i = 0;
switch (state) {
case 0:
if (i == 0) {
/*
* Here we want to set initial values for a, b, c an X,
* but I don't know how that is supposed to be done.
*/

for (unsigned long i = 0; i <= n; i++) {
a = 1 + ((a + c) % n);
b = 1 + ((b + a) % n);
c = 1 + ((c + b) % n);
X[i] += (unsigned long long)a * b * c * d + a;
X[i] &= mask_62_bits;
}
}

i += 1;
X[a] = (X[a] + X[b]) & mask_62_bits;

a = (a + c + i) & n;
state = 1;
return (X[a] + X[b]) & mask_56_bits;

case 1:
b = (b + a) & n;
state = 2;
return (X[b] + X[c]) & mask_56_bits;

case 2:
c = (c + b) & n;
state = 0;
return (X[c] + X[a]) & mask_56_bits;
}
}

int main(int argc, char **argv)
{
for (int i = 0; i < 100; i++)
printf("%llu\n", csprng());
}


--
Ben.

[James R. Kuyper]

If it can be done in C, it can generally also be done in C++, using
almost exactly the same code. There might also be a C++ way of doing it
that's better, using radically different code.

Note: regardless of what language you want to use, if this is a homework
assignment, many of the people who can give you the best help will
generally not give you that help until you've first made an attempt to
do it yourself. If your code doesn't work as intended, or maybe even
fails to compile, you can post your code here and people will be quite
happy to help you fix it - but they won't do your homework for you.

If this isn't homework, people who are competent to do so generally
expect to get paid for doing programming work for you. How much are you
willing to offer, and by what payment method?

[ribei...@gmail.com]

This is not homework nor commercial purposes.
See:
www.number.com/Melgo.html
From now on this subject will be dealt with in
https://groups.google.com/forum/#!forum/comp.lang.c

[ribei...@gmail.com]

Correction.
http://www.number.com.pt/Melgo.html