Function computeAndUpdateOuterECHExtension

ech.go:439–470

(outer, inner *clientHelloMsg, ech *echClientContext, useKey bool)

}

func computeAndUpdateOuterECHExtension(outer, inner *clientHelloMsg, ech *echClientContext, useKey bool) error {
	var encapKey []byte
	if useKey {
		encapKey = ech.encapsulatedKey
	}
	encodedInner, err := encodeInnerClientHello(inner, int(ech.config.MaxNameLength))
	if err != nil {
		return err
	}
	// NOTE: the tag lengths for all of the supported AEADs are the same (16
	// bytes), so we have hardcoded it here. If we add support for another AEAD
	// with a different tag length, we will need to change this.
	encryptedLen := len(encodedInner) + 16 // AEAD tag length
	outer.encryptedClientHello, err = generateOuterECHExt(ech.config.ConfigID, ech.kdfID, ech.aeadID, encapKey, make([]byte, encryptedLen))
	if err != nil {
		return err
	}
	serializedOuter, err := outer.marshal()
	if err != nil {
		return err
	}
	serializedOuter = serializedOuter[4:] // strip the four byte prefix
	encryptedInner, err := ech.hpkeContext.Seal(serializedOuter, encodedInner)
	if err != nil {
		return err
	}
	outer.encryptedClientHello, err = generateOuterECHExt(ech.config.ConfigID, ech.kdfID, ech.aeadID, encapKey, encryptedInner)
	if err != nil {
		return err
	}
	return nil
}

// validDNSName is a rather rudimentary check for the validity of a DNS name.
// This is used to check if the public_name in a ECHConfig is valid when we are