shad-go/otp/cipher.go

//go:build !solution

package otp

import (
	"io"
)

type cipherReader struct {
	r    io.Reader
	prng io.Reader
}

type cipherWriter struct {
	w    io.Writer
	prng io.Reader
}

func (c *cipherReader) Read(p []byte) (n int, err error) {
	n, err = c.r.Read(p)
	if err != nil {
		if err == io.EOF {
			p = p[:n]
		} else {
			return
		}
	}
	rand := make([]byte, n)
	_, rngErr := c.prng.Read(rand)
	if rngErr != nil {
		return
	}
	for i := 0; i < n; i++ {
		p[i] ^= rand[i]
	}
	return
}

func (c *cipherWriter) Write(p []byte) (n int, err error) {
	data := make([]byte, len(p))
	_, err = c.prng.Read(data)
	if err != nil {
		return
	}
	for i := 0; i < len(p); i++ {
		data[i] ^= p[i]
	}
	n, err = c.w.Write(data)
	return
}

func NewReader(r io.Reader, prng io.Reader) io.Reader {
	return &cipherReader{r, prng}
}

func NewWriter(w io.Writer, prng io.Reader) io.Writer {
	return &cipherWriter{w, prng}
}