CircuitCam license decoder

licdec.go

package main

import (
	"bytes"
	"crypto/rsa"
	"crypto/x509"
	"encoding/binary"
	"fmt"
	"math/big"
	"os"
)

var der = [...]byte{
	0x30, 0x81, 0x9F, 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01,
	0x05, 0x00, 0x03, 0x81, 0x8D, 0x00, 0x30, 0x81, 0x89, 0x02, 0x81, 0x81, 0x00, 0xA3, 0x3E, 0xE9,
	0x90, 0x04, 0x5F, 0x03, 0x59, 0xFF, 0x69, 0x62, 0x1A, 0x86, 0x51, 0xF9, 0x26, 0xC7, 0x65, 0x08,
	0x90, 0xFB, 0x7B, 0xE7, 0xB9, 0xFF, 0x23, 0x7C, 0xA8, 0xE8, 0x5A, 0xF6, 0x11, 0x26, 0x00, 0x23,
	0xEF, 0xC7, 0x3B, 0x8E, 0x6C, 0x31, 0xA1, 0x42, 0x17, 0x9E, 0x4E, 0xC8, 0x9D, 0xC2, 0xA8, 0x35,
	0x17, 0x45, 0x2F, 0x43, 0xF3, 0x3E, 0xF4, 0x98, 0xCE, 0x20, 0x11, 0x02, 0x8D, 0xCB, 0x30, 0xC9,
	0x37, 0x03, 0xBD, 0x17, 0xB1, 0x4D, 0x2D, 0xB9, 0xEA, 0x4D, 0x86, 0x7B, 0xF9, 0x7C, 0x87, 0x62,
	0x4E, 0x01, 0xAD, 0x81, 0xCE, 0x11, 0x44, 0xB3, 0xF3, 0xB7, 0x03, 0x02, 0x13, 0x23, 0xEF, 0x12,
	0xB4, 0x0A, 0x8F, 0x72, 0xD0, 0xE7, 0x36, 0x03, 0x75, 0xCA, 0x02, 0x93, 0xCF, 0x24, 0x93, 0x2F,
	0xCB, 0x29, 0xAF, 0xBC, 0x17, 0x7B, 0x6C, 0xFD, 0xD9, 0x76, 0x16, 0xB3, 0x7F, 0x02, 0x03, 0x01,
	0x00, 0x01,
}

// https://stackoverflow.com/questions/44852289/decrypt-with-public-key
func RSA_public_decrypt(pubKey *rsa.PublicKey, data []byte) []byte {
	c := new(big.Int)
	m := new(big.Int)
	m.SetBytes(data)
	e := big.NewInt(int64(pubKey.E))
	c.Exp(m, e, pubKey.N)
	out := c.Bytes()
	skip := 0
	for i := 2; i < len(out); i++ {
		if i+1 >= len(out) {
			break
		}
		if out[i] == 0xff && out[i+1] == 0 {
			skip = i + 2
			break
		}
	}
	return out[skip:]
}

func main() {
	pub, err := x509.ParsePKIXPublicKey(der[:])

	if err != nil {
		panic(err)
	}

	dat, err := os.ReadFile("licence.lic")

	if err != nil {
		panic(err)
	}

	rdr := bytes.NewReader(dat)

	for {
		var slen uint16

		if err := binary.Read(rdr, binary.BigEndian, &slen); err != nil {
			break
		}

		enc := make([]byte, slen)

		if len, err := rdr.Read(enc); len != int(slen) || err != nil {
			break
		}

		dec := RSA_public_decrypt(pub.(*rsa.PublicKey), enc)

		fmt.Print(string(dec))
	}
}

Copy license.lic to the same directory and execute with go run licdec.go