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package tun
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import (
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	"crypto/sha256"
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	"encoding/binary"
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	"encoding/hex"
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	"fmt"
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	"strings"
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	"go.miragespace.co/specter/spec/chord"
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)
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const SessionAliasPrefix = "session:"
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const EphemeralLabelPrefix = "e1-"
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func lowerHex(s string) bool {
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	for _, c := range s {
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		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f')) {
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			return false
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		}
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	}
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	return true
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}
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func IsSessionAlias(addr string) bool {
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	return len(addr) == 40 && strings.HasPrefix(addr, SessionAliasPrefix) && lowerHex(addr[len(SessionAliasPrefix):])
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}
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func SessionAlias(inv [16]byte) string { return SessionAliasPrefix + hex.EncodeToString(inv[:]) }
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func EphemeralLabel(home uint64, spki []byte) (label string, inv [16]byte, err error) {
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	if home >= chord.MaxIdentitifer {
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		return "", inv, fmt.Errorf("home ID exceeds 48 bits")
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	}
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	var encoded [8]byte
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	binary.BigEndian.PutUint64(encoded[:], home)
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	h := sha256.New()
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	h.Write([]byte("specter/ephemeral/v1\x00"))
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	h.Write(encoded[2:])
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	h.Write(spki)
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	copy(inv[:], h.Sum(nil))
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	return EphemeralLabelPrefix + hex.EncodeToString(encoded[2:]) + hex.EncodeToString(inv[:]), inv, nil
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}
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func ParseEphemeralLabel(label string) (home uint64, inv [16]byte, ok bool) {
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	if len(label) != 47 || !strings.HasPrefix(label, EphemeralLabelPrefix) || !lowerHex(label[3:]) {
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		return
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	}
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	raw, _ := hex.DecodeString(label[3:])
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	for _, b := range raw[:6] {
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		home = home<<8 | uint64(b)
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	}
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	copy(inv[:], raw[6:])
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	return home, inv, true
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}