mirror of
https://github.com/cbeuw/Cloak.git
synced 2024-11-11 13:11:03 +00:00
76 lines
2.1 KiB
Go
76 lines
2.1 KiB
Go
package server
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import (
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"bytes"
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"crypto"
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"encoding/binary"
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"errors"
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"fmt"
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"github.com/cbeuw/Cloak/internal/ecdh"
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"github.com/cbeuw/Cloak/internal/util"
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"time"
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)
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type ClientInfo struct {
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UID []byte
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SessionId uint32
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ProxyMethod string
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EncryptionMethod byte
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Unordered bool
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}
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const (
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UNORDERED_FLAG = 0x01 // 0000 0001
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)
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var ErrInvalidPubKey = errors.New("public key has invalid format")
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var ErrCiphertextLength = errors.New("ciphertext has the wrong length")
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var ErrTimestampOutOfWindow = errors.New("timestamp is outside of the accepting window")
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// touchStone checks if a ClientHello came from a Cloak client by checking and decrypting the fields Cloak hides data in
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// It returns the ClientInfo, but it doesn't check if the UID is authorised
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func touchStone(ch *ClientHello, staticPv crypto.PrivateKey, now func() time.Time) (info ClientInfo, sharedSecret []byte, err error) {
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ephPub, ok := ecdh.Unmarshal(ch.random)
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if !ok {
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err = ErrInvalidPubKey
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return
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}
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sharedSecret = ecdh.GenerateSharedSecret(staticPv, ephPub)
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var keyShare []byte
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keyShare, err = parseKeyShare(ch.extensions[[2]byte{0x00, 0x33}])
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if err != nil {
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return
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}
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ciphertext := append(ch.sessionId, keyShare...)
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if len(ciphertext) != 64 {
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err = fmt.Errorf("%v: %v", ErrCiphertextLength, len(ciphertext))
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return
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}
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var plaintext []byte
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plaintext, err = util.AESGCMDecrypt(ch.random[0:12], sharedSecret, ciphertext)
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if err != nil {
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return
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}
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info = ClientInfo{
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UID: plaintext[0:16],
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SessionId: 0,
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ProxyMethod: string(bytes.Trim(plaintext[16:28], "\x00")),
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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]))
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clientTime := time.Unix(timestamp, 0)
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serverTime := now()
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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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