pnyx/packet.go

79 lines
2.0 KiB
Go

2024-04-03 18:52:04 -06:00
package pnyx
import (
"crypto/ed25519"
"crypto/rand"
"crypto/sha512"
"fmt"
"filippo.io/edwards25519"
)
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
}