305 lines
9.6 KiB
Go
305 lines
9.6 KiB
Go
package mqtpp
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import (
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"crypto/aes"
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"crypto/ecdh"
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"crypto/rand"
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"crypto/sha256"
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"crypto/subtle"
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"encoding/binary"
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"fmt"
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"strings"
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"unicode/utf8"
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"google.golang.org/protobuf/encoding/protowire"
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)
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// PKIChannelID 是固件在 ServiceEnvelope/MQTT topic 中标识 PKI 加密包时使用的字面量
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// 见 firmware/src/mqtt/MQTT.cpp 中 `channelId = isPKIEncrypted ? "PKI" : channels.getGlobalId(chIndex);`
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const PKIChannelID = "PKI"
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// pkcOverhead 与固件 MESHTASTIC_PKC_OVERHEAD 一致：8 字节 AES-CCM 认证标签 + 4 字节 extraNonce
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const pkcOverhead = 12
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// PKITextMessageBuildOptions 描述构造一条 PKI 加密 DM 所需的全部上下文
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type PKITextMessageBuildOptions struct {
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FromNodeNum uint32
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ToNodeNum uint32
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PacketID uint32
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GatewayID string
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ViaMQTT bool
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SenderPrivate []byte // X25519 32 字节私钥
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RecipientPub []byte // X25519 32 字节公钥
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SenderPublic []byte // 可选；附在 MeshPacket.public_key (tag 16)
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Text string
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}
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// BuildPKITextMessageServiceEnvelope 构造一条遵循固件实现的 PKI 私聊文本消息：
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// - data 包: portnum=TEXT_MESSAGE_APP, payload=text
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// - 共享密钥: SHA256(X25519(senderPriv, recipientPub))
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// - AES-CCM(M=8,L=2,AAD=0); nonce = packetId(8B LE) | fromNode(4B LE) | extraNonce(4B LE，覆盖 fromNode 后续 4 字节)
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// - encrypted bytes 末尾追加 8 字节 auth + 4 字节 extraNonce(LE)
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// - MeshPacket.channel = 0, pki_encrypted(tag17)=1
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// - ServiceEnvelope.channel_id 固定 "PKI"
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func BuildPKITextMessageServiceEnvelope(opts PKITextMessageBuildOptions) ([]byte, error) {
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if opts.FromNodeNum == 0 {
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return nil, fmt.Errorf("from node number is required")
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}
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if opts.ToNodeNum == 0 || opts.ToNodeNum == NodeNumBroadcast {
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return nil, fmt.Errorf("pki direct message requires a non-broadcast destination")
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}
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if opts.PacketID == 0 {
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return nil, fmt.Errorf("packet id is required")
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}
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if opts.Text == "" {
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return nil, fmt.Errorf("text is required")
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}
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if !utf8.ValidString(opts.Text) {
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return nil, fmt.Errorf("text must be valid utf-8")
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}
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if len(opts.SenderPrivate) != 32 {
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return nil, fmt.Errorf("sender private key must be 32 bytes")
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}
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if len(opts.RecipientPub) != 32 {
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return nil, fmt.Errorf("recipient public key must be 32 bytes")
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}
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if strings.TrimSpace(opts.GatewayID) == "" {
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opts.GatewayID = NodeNumToID(opts.FromNodeNum)
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}
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plaintext := buildDataPacket(textMessageApp, []byte(opts.Text))
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sharedKey, err := pkiSharedKey(opts.SenderPrivate, opts.RecipientPub)
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if err != nil {
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return nil, err
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}
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var extraNonceBuf [4]byte
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if _, err := rand.Read(extraNonceBuf[:]); err != nil {
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return nil, err
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}
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extraNonce := binary.LittleEndian.Uint32(extraNonceBuf[:])
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ciphertext, auth, err := aesCCMEncrypt(sharedKey, pkiNonce(opts.PacketID, opts.FromNodeNum, extraNonce), plaintext)
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if err != nil {
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return nil, err
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}
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encrypted := make([]byte, 0, len(ciphertext)+pkcOverhead)
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encrypted = append(encrypted, ciphertext...)
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encrypted = append(encrypted, auth...)
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encrypted = append(encrypted, extraNonceBuf[:]...)
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packet := buildPKIMeshPacket(opts.FromNodeNum, opts.ToNodeNum, opts.PacketID, opts.ViaMQTT, encrypted, opts.SenderPublic)
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return buildServiceEnvelope(packet, PKIChannelID, opts.GatewayID), nil
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}
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// pkiSharedKey 用 X25519 计算共享密钥，再做一次 SHA-256（与固件一致）。
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func pkiSharedKey(privateKey, publicKey []byte) ([]byte, error) {
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curve := ecdh.X25519()
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priv, err := curve.NewPrivateKey(privateKey)
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if err != nil {
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return nil, fmt.Errorf("invalid sender private key: %w", err)
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}
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pub, err := curve.NewPublicKey(publicKey)
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if err != nil {
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return nil, fmt.Errorf("invalid recipient public key: %w", err)
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}
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shared, err := priv.ECDH(pub)
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if err != nil {
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return nil, fmt.Errorf("x25519 ecdh failed: %w", err)
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}
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digest := sha256.Sum256(shared)
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return digest[:], nil
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}
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// pkiNonce 完整复刻固件 CryptoEngine::initNonce(fromNode, packetId, extraNonce) 的字节布局。
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// 固件实现（mesh/CryptoEngine.cpp）：
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//
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// memcpy(nonce + 0, &packetId, 8); // packetId 是 uint64，写入 nonce[0..8)
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// memcpy(nonce + 8, &fromNode, 4); // fromNode 写入 nonce[8..12)
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// if (extraNonce)
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// memcpy(nonce + 4, &extraNonce, 4); // extraNonce 覆盖 nonce[4..8)
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//
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// 因此 13 字节 nonce 布局为：packetId_lo(4B LE) | extraNonce_or_packetId_hi(4B LE) | fromNode(4B LE) | 0x00
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func pkiNonce(packetID, fromNode, extraNonce uint32) []byte {
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nonce := make([]byte, 16)
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binary.LittleEndian.PutUint64(nonce[0:8], uint64(packetID)) // packetId 是 uint64，高 32 位为 0
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binary.LittleEndian.PutUint32(nonce[8:12], fromNode)
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if extraNonce != 0 {
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binary.LittleEndian.PutUint32(nonce[4:8], extraNonce)
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}
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// CCM L=2 → nonce 占 15-L=13 字节
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return nonce[:13]
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}
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// aesCCMEncrypt 使用与固件相同的参数（AES-CCM, M=8 即 8 字节 tag, L=2, 无 AAD）。
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func aesCCMEncrypt(key, nonce, plaintext []byte) (ciphertext []byte, auth []byte, err error) {
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if len(nonce) != 13 {
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return nil, nil, fmt.Errorf("ccm nonce must be 13 bytes")
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, nil, err
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}
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const tagLen = 8
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if len(plaintext) > 0xffff {
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return nil, nil, fmt.Errorf("plaintext too large for L=2 ccm")
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}
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// CBC-MAC 鉴权
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var x [aes.BlockSize]byte
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var b [aes.BlockSize]byte
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b[0] = byte((tagLen-2)/2) << 3 // M', AAD=0 时 Adata=0
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b[0] |= byte(2 - 1) // L'=L-1
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copy(b[1:], nonce[:13])
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binary.BigEndian.PutUint16(b[14:], uint16(len(plaintext)))
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block.Encrypt(x[:], b[:])
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// 鉴权明文
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for offset := 0; offset < len(plaintext); offset += aes.BlockSize {
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end := offset + aes.BlockSize
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if end > len(plaintext) {
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end = len(plaintext)
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}
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var blk [aes.BlockSize]byte
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copy(blk[:], plaintext[offset:end])
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for i := range x {
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x[i] ^= blk[i]
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}
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block.Encrypt(x[:], x[:])
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}
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// CTR 流：A_i = L' | nonce | counter_be16
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var a [aes.BlockSize]byte
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a[0] = byte(2 - 1)
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copy(a[1:], nonce[:13])
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encryptCounter := func(i uint16) [aes.BlockSize]byte {
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var ai [aes.BlockSize]byte
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copy(ai[:], a[:])
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binary.BigEndian.PutUint16(ai[14:], i)
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var s [aes.BlockSize]byte
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block.Encrypt(s[:], ai[:])
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return s
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}
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ciphertext = make([]byte, len(plaintext))
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for i, offset := 1, 0; offset < len(plaintext); i, offset = i+1, offset+aes.BlockSize {
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s := encryptCounter(uint16(i))
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end := offset + aes.BlockSize
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if end > len(plaintext) {
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end = len(plaintext)
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}
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for j := offset; j < end; j++ {
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ciphertext[j] = plaintext[j] ^ s[j-offset]
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}
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}
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// auth = T XOR S_0
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s0 := encryptCounter(0)
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auth = make([]byte, tagLen)
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for i := 0; i < tagLen; i++ {
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auth[i] = x[i] ^ s0[i]
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}
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return ciphertext, auth, nil
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}
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// aesCCMDecrypt 与 encrypt 对称，验证标签后返回明文。仅用于测试与可能的回程解密。
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func aesCCMDecrypt(key, nonce, ciphertext, auth []byte) ([]byte, error) {
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if len(nonce) != 13 {
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return nil, fmt.Errorf("ccm nonce must be 13 bytes")
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}
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if len(auth) != 8 {
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return nil, fmt.Errorf("ccm auth tag must be 8 bytes")
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}
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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// 先 CTR 解密
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var a [aes.BlockSize]byte
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a[0] = byte(2 - 1)
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copy(a[1:], nonce[:13])
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encryptCounter := func(i uint16) [aes.BlockSize]byte {
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var ai [aes.BlockSize]byte
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copy(ai[:], a[:])
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binary.BigEndian.PutUint16(ai[14:], i)
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var s [aes.BlockSize]byte
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block.Encrypt(s[:], ai[:])
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return s
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}
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plain := make([]byte, len(ciphertext))
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for i, offset := 1, 0; offset < len(ciphertext); i, offset = i+1, offset+aes.BlockSize {
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s := encryptCounter(uint16(i))
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end := offset + aes.BlockSize
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if end > len(ciphertext) {
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end = len(ciphertext)
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}
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for j := offset; j < end; j++ {
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plain[j] = ciphertext[j] ^ s[j-offset]
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}
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}
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// 再 CBC-MAC 校验
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var x [aes.BlockSize]byte
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var b [aes.BlockSize]byte
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b[0] = byte((8-2)/2) << 3
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b[0] |= byte(2 - 1)
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copy(b[1:], nonce[:13])
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binary.BigEndian.PutUint16(b[14:], uint16(len(plain)))
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block.Encrypt(x[:], b[:])
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for offset := 0; offset < len(plain); offset += aes.BlockSize {
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end := offset + aes.BlockSize
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if end > len(plain) {
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end = len(plain)
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}
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var blk [aes.BlockSize]byte
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copy(blk[:], plain[offset:end])
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for i := range x {
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x[i] ^= blk[i]
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}
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block.Encrypt(x[:], x[:])
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}
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s0 := encryptCounter(0)
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expected := make([]byte, 8)
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for i := 0; i < 8; i++ {
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expected[i] = x[i] ^ s0[i]
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}
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if subtle.ConstantTimeCompare(expected, auth) != 1 {
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return nil, fmt.Errorf("aes-ccm auth mismatch")
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}
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return plain, nil
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}
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// buildPKIMeshPacket 构造一个 PKI 加密的 MeshPacket：
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// - tag 1/2: from/to (fixed32)
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// - tag 3 channel = 0 （省略，默认即为 0）
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// - tag 5 encrypted (含 ciphertext|auth|extraNonce)
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// - tag 6 packet_id
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// - tag 14 via_mqtt
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// - tag 16 public_key（可选，附带发送者公钥）
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// - tag 17 pki_encrypted = 1
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func buildPKIMeshPacket(from, to, packetID uint32, viaMQTT bool, encrypted []byte, senderPublic []byte) []byte {
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var out []byte
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out = protowire.AppendTag(out, 1, protowire.Fixed32Type)
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out = protowire.AppendFixed32(out, from)
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out = protowire.AppendTag(out, 2, protowire.Fixed32Type)
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out = protowire.AppendFixed32(out, to)
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out = protowire.AppendTag(out, 5, protowire.BytesType)
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out = protowire.AppendBytes(out, encrypted)
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out = protowire.AppendTag(out, 6, protowire.Fixed32Type)
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out = protowire.AppendFixed32(out, packetID)
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if viaMQTT {
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out = protowire.AppendTag(out, 14, protowire.VarintType)
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out = protowire.AppendVarint(out, 1)
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}
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if len(senderPublic) == 32 {
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out = protowire.AppendTag(out, 16, protowire.BytesType)
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out = protowire.AppendBytes(out, senderPublic)
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}
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out = protowire.AppendTag(out, 17, protowire.VarintType)
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out = protowire.AppendVarint(out, 1)
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return out
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}
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