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package extension
import "encoding/binary"
const (
useExtendedMasterSecretHeaderSize = 4
)
// UseExtendedMasterSecret defines a TLS extension that contextually binds the
// master secret to a log of the full handshake that computes it, thus
// preventing MITM attacks.
type UseExtendedMasterSecret struct {
Supported bool
}
// TypeValue returns the extension TypeValue
func (u UseExtendedMasterSecret) TypeValue() TypeValue {
return UseExtendedMasterSecretTypeValue
}
// Marshal encodes the extension
func (u *UseExtendedMasterSecret) Marshal() ([]byte, error) {
if !u.Supported {
return []byte{}, nil
}
out := make([]byte, useExtendedMasterSecretHeaderSize)
binary.BigEndian.PutUint16(out, uint16(u.TypeValue()))
binary.BigEndian.PutUint16(out[2:], uint16(0)) // length
return out, nil
}
// Unmarshal populates the extension from encoded data
func (u *UseExtendedMasterSecret) Unmarshal(data []byte) error {
if len(data) < useExtendedMasterSecretHeaderSize {
return errBufferTooSmall
} else if TypeValue(binary.BigEndian.Uint16(data)) != u.TypeValue() {
return errInvalidExtensionType
}
u.Supported = true
return nil
}
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