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59 lines
2.1 KiB
Go
59 lines
2.1 KiB
Go
package client
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import (
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"crypto/rand"
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"encoding/binary"
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"github.com/cbeuw/Cloak/internal/ecdh"
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"github.com/cbeuw/Cloak/internal/util"
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"sync/atomic"
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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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type chHiddenData struct {
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fullRaw []byte // pubkey, ciphertext, tag
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chRandom []byte
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chSessionId []byte
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chX25519KeyShare []byte
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chExtSNI []byte
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}
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// makeHiddenData generates the ephemeral key pair, calculates the shared secret, and then compose and
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// encrypt the Authentication data. It also composes SNI extension.
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func makeHiddenData(sta *State) (ret chHiddenData, sharedSecret []byte) {
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// random is marshalled ephemeral pub key 32 bytes
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/*
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Authentication data:
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+----------+----------------+---------------------+-------------+--------------+--------+------------+
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| _UID_ | _Proxy Method_ | _Encryption Method_ | _Timestamp_ | _Session Id_ | _Flag_ | _reserved_ |
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+----------+----------------+---------------------+-------------+--------------+--------+------------+
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| 16 bytes | 12 bytes | 1 byte | 8 bytes | 4 bytes | 1 byte | 6 bytes |
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+----------+----------------+---------------------+-------------+--------------+--------+------------+
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*/
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// The authentication ciphertext and its tag are then distributed among SessionId and X25519KeyShare
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ephPv, ephPub, _ := ecdh.GenerateKey(rand.Reader)
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ret.chRandom = ecdh.Marshal(ephPub)
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plaintext := make([]byte, 48)
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copy(plaintext, sta.UID)
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copy(plaintext[16:28], sta.ProxyMethod)
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plaintext[28] = sta.EncryptionMethod
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binary.BigEndian.PutUint64(plaintext[29:37], uint64(sta.Now().Unix()))
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binary.BigEndian.PutUint32(plaintext[37:41], atomic.LoadUint32(&sta.SessionID))
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if sta.Unordered {
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plaintext[41] |= UNORDERED_FLAG
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}
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sharedSecret = ecdh.GenerateSharedSecret(ephPv, sta.staticPub)
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nonce := ret.chRandom[0:12]
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ciphertextWithTag, _ := util.AESGCMEncrypt(nonce, sharedSecret, plaintext)
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ret.fullRaw = append(ret.chRandom, ciphertextWithTag...)
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ret.chSessionId = ciphertextWithTag[0:32]
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ret.chX25519KeyShare = ciphertextWithTag[32:64]
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ret.chExtSNI = makeServerName(sta.ServerName)
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return
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}
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