Cloak/internal/server/auth.go

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package server
import (
"bytes"
"encoding/binary"
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"errors"
"fmt"
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"github.com/cbeuw/Cloak/internal/common"
"time"
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log "github.com/sirupsen/logrus"
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)
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type ClientInfo struct {
UID []byte
SessionId uint32
ProxyMethod string
EncryptionMethod byte
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Unordered bool
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Transport Transport
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}
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type authFragments struct {
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sharedSecret [32]byte
randPubKey [32]byte
ciphertextWithTag [64]byte
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}
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const (
UNORDERED_FLAG = 0x01 // 0000 0001
)
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var ErrTimestampOutOfWindow = errors.New("timestamp is outside of the accepting window")
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// decryptClientInfo checks if a the authFragments are valid. It doesn't check if the UID is authorised
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func decryptClientInfo(fragments authFragments, serverTime time.Time) (info ClientInfo, err error) {
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var plaintext []byte
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plaintext, err = common.AESGCMDecrypt(fragments.randPubKey[0:12], fragments.sharedSecret[:], fragments.ciphertextWithTag[:])
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if err != nil {
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return
}
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info = ClientInfo{
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UID: plaintext[0:16],
SessionId: 0,
ProxyMethod: string(bytes.Trim(plaintext[16:28], "\x00")),
EncryptionMethod: plaintext[28],
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Unordered: plaintext[41]&UNORDERED_FLAG != 0,
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}
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timestamp := int64(binary.BigEndian.Uint64(plaintext[29:37]))
clientTime := time.Unix(timestamp, 0)
if !(clientTime.After(serverTime.Truncate(TIMESTAMP_TOLERANCE)) && clientTime.Before(serverTime.Add(TIMESTAMP_TOLERANCE))) {
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err = fmt.Errorf("%v: received timestamp %v", ErrTimestampOutOfWindow, timestamp)
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return
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}
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info.SessionId = binary.BigEndian.Uint32(plaintext[37:41])
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return
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}
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var ErrReplay = errors.New("duplicate random")
var ErrBadProxyMethod = errors.New("invalid proxy method")
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var ErrBadDecryption = errors.New("decryption/authentication faliure")
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// AuthFirstPacket checks if the first packet of data is ClientHello or HTTP GET, and checks if it was from a Cloak client
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// if it is from a Cloak client, it returns the ClientInfo with the decrypted fields. It doesn't check if the user
// is authorised. It also returns a finisher callback function to be called when the caller wishes to proceed with
// the handshake
func AuthFirstPacket(firstPacket []byte, transport Transport, sta *State) (info ClientInfo, finisher Responder, err error) {
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fragments, finisher, err := transport.processFirstPacket(firstPacket, sta.StaticPv)
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if err != nil {
return
}
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if sta.registerRandom(fragments.randPubKey) {
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err = ErrReplay
return
}
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info, err = decryptClientInfo(fragments, sta.WorldState.Now())
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if err != nil {
log.Debug(err)
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err = fmt.Errorf("%w: %v", ErrBadDecryption, err)
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return
}
if _, ok := sta.ProxyBook[info.ProxyMethod]; !ok {
err = ErrBadProxyMethod
return
}
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info.Transport = transport
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return
}