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60 lines
1.6 KiB
Go
60 lines
1.6 KiB
Go
package server
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import (
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"bytes"
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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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)
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var ErrReplay = errors.New("duplicate random")
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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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func TouchStone(ch *ClientHello, sta *State) (UID []byte, sessionID uint32, proxyMethod string, encryptionMethod byte, sharedSecret []byte, err error) {
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if sta.registerRandom(ch.random) {
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err = ErrReplay
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return
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}
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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(sta.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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UID = plaintext[0:16]
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proxyMethod = string(bytes.Trim(plaintext[16:28], "\x00"))
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encryptionMethod = plaintext[28]
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timestamp := int64(binary.BigEndian.Uint64(plaintext[29:37]))
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if timestamp/int64(TIMESTAMP_WINDOW.Seconds()) != sta.Now().Unix()/int64(TIMESTAMP_WINDOW.Seconds()) {
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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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sessionID = binary.BigEndian.Uint32(plaintext[37:41])
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return
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}
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