Deterministic crypto/rand Reader

determ_crypto_reader.go

// WARNING: This is a bad idea.
// Instead, use a Deterministic random bit generator specified in NIST SP 800-90A
// Unverified Go implementation from the TOR project:
//  https://gist.github.com/jpillora/ed5cf69af7d35f9bb5f1












// Deterministic crypto/rand Reader
//
// Overview: half the result is used as the output,
// the other half is used as the next input
//
// [a|b] -> sha512(a) -> [a'|b'] -> sha512(a') -> [a''|b'']
//    |                      |                         |
//  output                 output                    output

package dcrypto

import (
	"crypto/sha512"
	"io"
)

func NewDetermRand(seed []byte) io.Reader {
	return &DetermRand{next: seed}
}

type DetermRand struct {
	next []byte
}

func (d *DetermRand) cycle() []byte {
	result := sha512.Sum512(d.next)
	d.next = result[:sha512.Size/2]
	return result[sha512.Size/2:]
}

func (d *DetermRand) Read(b []byte) (int, error) {
	n := 0
	for n < len(b) {
		out := d.cycle()
		n += copy(b[n:], out)
	}
	return n, nil
}

Run it here https://go-sandbox.com/#/kX-LptvhoF

If you dont need strong crypto randomness, you can use https://github.com/dustin/randbo to get the reader interface over math/rand

@whyrusleeping how would you seed it with a []byte? Hash then take 8 bytes to convert to int64?