mediamtx/internal/rtmp/handshake/c1.go

package handshake

import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"io"
)

var (
	hsClientFullKey = []byte{
		'G', 'e', 'n', 'u', 'i', 'n', 'e', ' ', 'A', 'd', 'o', 'b', 'e', ' ',
		'F', 'l', 'a', 's', 'h', ' ', 'P', 'l', 'a', 'y', 'e', 'r', ' ',
		'0', '0', '1',
		0xF0, 0xEE, 0xC2, 0x4A, 0x80, 0x68, 0xBE, 0xE8, 0x2E, 0x00, 0xD0, 0xD1,
		0x02, 0x9E, 0x7E, 0x57, 0x6E, 0xEC, 0x5D, 0x2D, 0x29, 0x80, 0x6F, 0xAB,
		0x93, 0xB8, 0xE6, 0x36, 0xCF, 0xEB, 0x31, 0xAE,
	}
	hsServerFullKey = []byte{
		'G', 'e', 'n', 'u', 'i', 'n', 'e', ' ', 'A', 'd', 'o', 'b', 'e', ' ',
		'F', 'l', 'a', 's', 'h', ' ', 'M', 'e', 'd', 'i', 'a', ' ',
		'S', 'e', 'r', 'v', 'e', 'r', ' ',
		'0', '0', '1',
		0xF0, 0xEE, 0xC2, 0x4A, 0x80, 0x68, 0xBE, 0xE8, 0x2E, 0x00, 0xD0, 0xD1,
		0x02, 0x9E, 0x7E, 0x57, 0x6E, 0xEC, 0x5D, 0x2D, 0x29, 0x80, 0x6F, 0xAB,
		0x93, 0xB8, 0xE6, 0x36, 0xCF, 0xEB, 0x31, 0xAE,
	}
	hsClientPartialKey = hsClientFullKey[:30]
	hsServerPartialKey = hsServerFullKey[:36]
)

func hsCalcDigestPos(p []byte, base int) (pos int) {
	for i := 0; i < 4; i++ {
		pos += int(p[base+i])
	}
	pos = (pos % 728) + base + 4
	return
}

func hsMakeDigest(key []byte, src []byte, gap int) (dst []byte) {
	h := hmac.New(sha256.New, key)
	if gap <= 0 {
		h.Write(src)
	} else {
		h.Write(src[:gap])
		h.Write(src[gap+32:])
	}
	return h.Sum(nil)
}

// C1 is the C1 part of an handshake.
type C1 struct{}

// Read reads a C1.
func (C1) Write(w io.Writer) error {
	buf := make([]byte, 1536)
	copy(buf[0:4], []byte{0x00, 0x00, 0x00, 0x00})
	copy(buf[4:8], []byte{0x09, 0x00, 0x7c, 0x02})

	rand.Read(buf[8:])
	gap := hsCalcDigestPos(buf[0:], 8)
	digest := hsMakeDigest(hsClientPartialKey, buf[0:], gap)
	copy(buf[gap+0:], digest)

	_, err := w.Write(buf[0:])
	return err
}