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package handshake
import (
"encoding/binary"
)
// MessageClientKeyExchange is a DTLS Handshake Message
// With this message, the premaster secret is set, either by direct
// transmission of the RSA-encrypted secret or by the transmission of
// Diffie-Hellman parameters that will allow each side to agree upon
// the same premaster secret.
//
// https://tools.ietf.org/html/rfc5246#section-7.4.7
type MessageClientKeyExchange struct {
IdentityHint []byte
PublicKey []byte
}
// Type returns the Handshake Type
func (m MessageClientKeyExchange) Type() Type {
return TypeClientKeyExchange
}
// Marshal encodes the Handshake
func (m *MessageClientKeyExchange) Marshal() ([]byte, error) {
switch {
case (m.IdentityHint != nil && m.PublicKey != nil) || (m.IdentityHint == nil && m.PublicKey == nil):
return nil, errInvalidClientKeyExchange
case m.PublicKey != nil:
return append([]byte{byte(len(m.PublicKey))}, m.PublicKey...), nil
default:
out := append([]byte{0x00, 0x00}, m.IdentityHint...)
binary.BigEndian.PutUint16(out, uint16(len(out)-2))
return out, nil
}
}
// Unmarshal populates the message from encoded data
func (m *MessageClientKeyExchange) Unmarshal(data []byte) error {
if len(data) < 2 {
return errBufferTooSmall
}
// If parsed as PSK return early and only populate PSK Identity Hint
if pskLength := binary.BigEndian.Uint16(data); len(data) == int(pskLength+2) {
m.IdentityHint = append([]byte{}, data[2:]...)
return nil
}
if publicKeyLength := int(data[0]); len(data) != publicKeyLength+1 {
return errBufferTooSmall
}
m.PublicKey = append([]byte{}, data[1:]...)
return nil
}
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