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package crypto
import (
"github.com/bifurcation/mint"
"github.com/lucas-clemente/quic-go/internal/protocol"
)
const (
clientExporterLabel = "EXPORTER-QUIC client 1-RTT Secret"
serverExporterLabel = "EXPORTER-QUIC server 1-RTT Secret"
)
// A TLSExporter gets the negotiated ciphersuite and computes exporter
type TLSExporter interface {
GetCipherSuite() mint.CipherSuiteParams
ComputeExporter(label string, context []byte, keyLength int) ([]byte, error)
}
// DeriveAESKeys derives the AES keys and creates a matching AES-GCM AEAD instance
func DeriveAESKeys(tls TLSExporter, pers protocol.Perspective) (AEAD, error) {
var myLabel, otherLabel string
if pers == protocol.PerspectiveClient {
myLabel = clientExporterLabel
otherLabel = serverExporterLabel
} else {
myLabel = serverExporterLabel
otherLabel = clientExporterLabel
}
myKey, myIV, err := computeKeyAndIV(tls, myLabel)
if err != nil {
return nil, err
}
otherKey, otherIV, err := computeKeyAndIV(tls, otherLabel)
if err != nil {
return nil, err
}
return NewAEADAESGCM(otherKey, myKey, otherIV, myIV)
}
func computeKeyAndIV(tls TLSExporter, label string) (key, iv []byte, err error) {
cs := tls.GetCipherSuite()
secret, err := tls.ComputeExporter(label, nil, cs.Hash.Size())
if err != nil {
return nil, nil, err
}
key = mint.HkdfExpandLabel(cs.Hash, secret, "key", nil, cs.KeyLen)
iv = mint.HkdfExpandLabel(cs.Hash, secret, "iv", nil, cs.IvLen)
return key, iv, nil
}