pnyx/packet.go

159 lines
4.2 KiB
Go

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package pnyx
import (
"crypto/ed25519"
"crypto/rand"
"crypto/sha512"
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"encoding/binary"
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"fmt"
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"slices"
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"filippo.io/edwards25519"
)
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type PacketType uint16
const (
ID_LENGTH = 16
PUBKEY_LENGTH = 32
ECDH_LENGTH = 32
SIGNATURE_LENGTH = 64
HMAC_LENGTH = 64
SESSION_OPEN_LENGTH = PUBKEY_LENGTH + ECDH_LENGTH + SIGNATURE_LENGTH
SESSION_CONNECT_LENGTH = ID_LENGTH + 2 + HMAC_LENGTH // + return addr string length
SESSION_OPEN PacketType = iota
SESSION_CONNECT
SESSION_CLOSE
SESSION_CLOSED
SESSION_DATA
)
func SessionKeyID(session_secret []byte) SessionID {
hash := sha512.Sum512(session_secret)
return (SessionID)(hash[0:16])
}
func NewSessionConnect(address string, session_secret []byte) []byte {
packet := make([]byte, SESSION_CONNECT_LENGTH + len(address))
cur := 0
session_id := [16]byte(SessionKeyID(session_secret))
copy(packet[cur:], session_id[:])
cur += ID_LENGTH
binary.BigEndian.PutUint16(packet[cur:], uint16(len(address)))
cur += 2
copy(packet[cur:], []byte(address))
cur += len(address)
hmac := sha512.Sum512(append(packet[:cur], session_secret...))
copy(packet[cur:], hmac[:])
return packet
}
func ParseSessionConnect(session_connect []byte, session_secret []byte) (SessionID, string, error) {
if len(session_connect) < SESSION_CONNECT_LENGTH {
return SessionID{}, "", fmt.Errorf("Bad session connect length: %d/%d", len(session_connect), SESSION_CONNECT_LENGTH)
}
cur := 0
session_id := SessionID(session_connect[cur:cur+ID_LENGTH])
cur += ID_LENGTH
address_length := int(binary.BigEndian.Uint16(session_connect[cur:cur+2]))
cur += 2
if len(session_connect) != (SESSION_CONNECT_LENGTH + address_length) {
return SessionID{}, "", fmt.Errorf("Bad session connect length: %d/%d", len(session_connect), SESSION_CONNECT_LENGTH + address_length)
}
address := string(session_connect[cur:cur+address_length])
cur += address_length
hmac_digest := make([]byte, cur)
copy(hmac_digest, session_connect[:cur])
hmac := session_connect[cur:cur+HMAC_LENGTH]
cur += HMAC_LENGTH
calculated_hmac := sha512.Sum512(append(hmac_digest, session_secret...))
if slices.Compare(hmac, calculated_hmac[:]) != 0 {
return SessionID{}, "", fmt.Errorf("Session connect bad HMAC")
}
return session_id, address, nil
}
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func NewSessionOpen(key ed25519.PrivateKey) ([]byte, ed25519.PrivateKey, error) {
if key == nil {
return nil, nil, fmt.Errorf("Cannot create a SESSION_OPEN packet without a key")
}
public, private, err := ed25519.GenerateKey(rand.Reader)
if err != nil {
return nil, nil, fmt.Errorf("Failed to generate ecdh key: %w", err)
}
packet := make([]byte, SESSION_OPEN_LENGTH)
cur := 0
copy(packet[cur:], []byte(key.Public().(ed25519.PublicKey)))
cur += PUBKEY_LENGTH
copy(packet[cur:], []byte(public))
cur += PUBKEY_LENGTH
signature := ed25519.Sign(key, packet[:cur])
copy(packet[cur:], signature)
cur += SIGNATURE_LENGTH
return packet, private, nil
}
func ParseSessionOpen(session_open []byte) (ed25519.PublicKey, ed25519.PublicKey, error) {
if len(session_open) != SESSION_OPEN_LENGTH {
return nil, nil, fmt.Errorf("Bad SESSION_OPEN length: %d/%d", len(session_open), SESSION_OPEN_LENGTH)
}
cur := 0
client_pubkey := (ed25519.PublicKey)(session_open[cur:cur+PUBKEY_LENGTH])
cur += PUBKEY_LENGTH
client_ecdh := (ed25519.PublicKey)(session_open[cur:cur+PUBKEY_LENGTH])
cur += PUBKEY_LENGTH
digest := session_open[:cur]
signature := session_open[cur:cur+SIGNATURE_LENGTH]
cur += SIGNATURE_LENGTH
if ed25519.Verify(client_pubkey, digest, signature) == false {
return nil, nil, fmt.Errorf("SESSION_OPEN signature verification failed")
}
return client_pubkey, client_ecdh, nil
}
func ECDH(public ed25519.PublicKey, private ed25519.PrivateKey) ([]byte, error) {
public_point, err := (&edwards25519.Point{}).SetBytes(public)
if err != nil {
return nil, err
}
h := sha512.Sum512(private.Seed())
private_scalar, err := (&edwards25519.Scalar{}).SetBytesWithClamping(h[:32])
if err != nil {
return nil, err
}
shared_point := public_point.ScalarMult(private_scalar, public_point)
return shared_point.BytesMontgomery(), nil
}