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drkey.go
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drkey.go
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// Copyright 2017 ETH Zurich
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// DRKeyMac:
//
// 0B 1 2 3 4 5 6 7
// +--------+--------+--------+--------+--------+--------+--------+--------+
// | xxxxxxxxxxxxxxxxxxxxxxxx | 0x04 | dir | padding |
// +--------+--------+--------+--------+--------+--------+--------+--------+
// | DRKey MAC |
// +--------+--------+--------+--------+--------+--------+--------+--------+
// | DRKey MAC (continued) |
// +--------+--------+--------+--------+--------+--------+--------+--------+
//
package scmp_auth
import (
"bytes"
"fmt"
"github.com/scionproto/scion/go/lib/common"
"github.com/scionproto/scion/go/lib/spse"
)
var _ common.Extension = (*DRKeyExtn)(nil)
// DRKeyExtn is an implementation of the SCMPAuthDRKey extension.
// It is used to authenticate scmp messages.
type DRKeyExtn struct {
*spse.BaseExtn
// Direction indicates which key has been used during authentication.
Direction Dir
// MAC is the mac of the SCION Packet with CurrHF and CurrINF set to zero.
MAC common.RawBytes
}
const (
DirectionLength = 1
PaddingLength = 3
MACLength = 16
DirectionOffset = spse.SecModeLength
MACOffset = DirectionOffset + DirectionLength + PaddingLength
DRKeyTotalLength = MACOffset + MACLength
)
type Dir uint8
const (
AsToAs Dir = iota // Authenticated with S -> D
AsToHost // Authenticated with S -> D:HD
HostToHost // Authenticated with S:HS -> D:HD
HostToAs // Authenticated with D -> S:HS
AsToAsReversed // Authenticated with D -> S
HostToHostReversed // Authenticated with D:HD -> S:HS
)
func (d Dir) String() string {
switch d {
case AsToAs:
return "AS to AS"
case AsToHost:
return "AS to Host"
case HostToHost:
return "Host to Host"
case HostToAs:
return "Host to AS"
case AsToAsReversed:
return "AS to AS reversed"
case HostToHostReversed:
return "Host to Host reversed"
default:
return fmt.Sprintf("UNKNOWN: %v", uint8(d))
}
}
func NewDRKeyExtn() *DRKeyExtn {
s := &DRKeyExtn{BaseExtn: &spse.BaseExtn{SecMode: spse.ScmpAuthDRKey}}
s.MAC = make(common.RawBytes, MACLength)
return s
}
func (s DRKeyExtn) SetDirection(dir Dir) error {
if dir > HostToHostReversed {
return common.NewBasicError("Invalid direction", nil, "dir", dir)
}
s.Direction = dir
return nil
}
func (s DRKeyExtn) SetMAC(mac common.RawBytes) error {
if len(mac) != MACLength {
return common.NewBasicError("Invalid MAC size", nil,
"expected", MACLength, "actual", len(mac))
}
copy(s.MAC, mac)
return nil
}
func (s *DRKeyExtn) Write(b common.RawBytes) error {
if len(b) < s.Len() {
return common.NewBasicError("Buffer too short", nil,
"method", "SCMPAuthDRKeyExtn.Write", "expected", s.Len(), "actual", len(b))
}
b[0] = uint8(s.SecMode)
b[DirectionOffset] = uint8(s.Direction)
for i := DirectionOffset + DirectionLength; i < MACOffset; i++ {
b[i] = 0
}
copy(b[MACOffset:DRKeyTotalLength], s.MAC)
return nil
}
func (s *DRKeyExtn) Pack() (common.RawBytes, error) {
b := make(common.RawBytes, s.Len())
if err := s.Write(b); err != nil {
return nil, err
}
return b, nil
}
func (s *DRKeyExtn) Copy() common.Extension {
c := NewDRKeyExtn()
c.Direction = s.Direction
copy(c.MAC, s.MAC)
return c
}
func (s *DRKeyExtn) Len() int {
return DRKeyTotalLength
}
func (s *DRKeyExtn) String() string {
buf := &bytes.Buffer{}
fmt.Fprintf(buf, "AuthDRKeyExtn (%dB): SecMode: %d\n", s.Len(), s.SecMode)
fmt.Fprintf(buf, " Direction: %x", s.Direction)
fmt.Fprintf(buf, " MAC: %s", s.MAC.String())
return buf.String()
}