keyvis.go

package main

import (
	"encoding/base64"
	"fmt"
	"os"
	"strings"
)

const (
	FieldBase  = 16 // size of the matrix
	FieldSizeX = FieldBase + 1
	FieldSizeY = 2*FieldBase + 1
)

func max(a, b int) int {
	if a < b {
		return b
	}

	return a
}

func min(a, b int) int {
	if a > b {
		return b
	}

	return a
}

// RandomArt is the internal representation of a randomart image
type RandomArt [FieldSizeX][FieldSizeY]byte

// generate randomart matrix
// i have no idea what im doing. port of openssh randomart.
// https://github.com/openssh/openssh-portable/blob/271df8185d9689b3fb0523f58514481b858f6843/sshkey.c#L1051
func randomart(key []byte) RandomArt {
	var innerLoop = [4]int{0, 1, 2, 3}

	field := [FieldSizeX][FieldSizeY]byte{}
	x, y := FieldSizeX/2, FieldSizeY/2

	for _, input := range key {
		for _ = range innerLoop {
			switch input & 0x1 {
			case 1:
				x += 1
			case 0:
				x -= 1
			}

			switch input & 0x2 {
			case 2:
				y += 1
			case 0:
				y -= 1
			}

			/* assure we are still in bounds */
			x = max(x, 0)
			y = max(y, 0)
			x = min(x, FieldSizeX-1)
			y = min(y, FieldSizeY-1)

			/* augment the field */
			if int(field[x][y]) < len(key)-2 {
				field[x][y]++
			}
			input = input >> 2
		}

	}

	return field
}

//print colorized ssh-style randomart
func plot(art RandomArt, id string) {
	syms := []string{
		" ",
		".",
		"o",
		"+",
		"=",
		"*",
		"B",
		"O",
		"X", // maybe somebody wants to
		"@", // add more color escapes?
		"%", // i ran out of ideas for
		"&", // the moment.
		"#",
		"/",
		"^",
		"S",
		"E",
	}
	spaces := ""

	for i := 0; i < (len(id)-FieldSizeY)/2-1; i++ {
		spaces += " "
	}

	fmt.Println(id)
	for _, line := range art {
		fmt.Print(spaces + "|")
		for _, char := range line {
			fmt.Printf("%s", syms[char])
		}
		fmt.Println("|")
	}

}

// print matlab surf command
func surf(art RandomArt) {
	fmt.Println("% put this into matlab or octave")
	fmt.Println("surf([")
	for _, line := range art {
		fmt.Print("[")
		for _, char := range line {
			fmt.Print(char, ",")
		}
		fmt.Println("];")
	}
	fmt.Println("]);")
}

func main() {
	if len(os.Args) < 2 {
		fmt.Printf("Usage: %s <id>\n", os.Args[0])
		return
	}

	id := os.Args[1]
	if id[0] != '@' || strings.Split(id[1:], ".")[1] != "ed25519" {
		fmt.Println("error: that does not look like an id.")
		return
	}

	b64Key := strings.Split(id[1:], ".")[0]

	key, err := base64.StdEncoding.DecodeString(b64Key)
	if err != nil {
		fmt.Println("error parsing public key:", err)
		return
	}

	art := randomart(key)

	//	plot(art, id)
	surf(art)
}