添加 github.com/pion/dtls 代码

dtls-2.0.9/pkg/crypto/ciphersuite/cbc.go

@@ -0,0 +1,164 @@
+package ciphersuite
+
+import ( //nolint:gci
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/hmac"
+	"crypto/rand"
+	"encoding/binary"
+	"hash"
+
+	"github.com/pion/dtls/v2/internal/util"
+	"github.com/pion/dtls/v2/pkg/crypto/prf"
+	"github.com/pion/dtls/v2/pkg/protocol"
+	"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
+)
+
+// block ciphers using cipher block chaining.
+type cbcMode interface {
+	cipher.BlockMode
+	SetIV([]byte)
+}
+
+// CBC Provides an API to Encrypt/Decrypt DTLS 1.2 Packets
+type CBC struct {
+	writeCBC, readCBC cbcMode
+	writeMac, readMac []byte
+	h                 prf.HashFunc
+}
+
+// NewCBC creates a DTLS CBC Cipher
+func NewCBC(localKey, localWriteIV, localMac, remoteKey, remoteWriteIV, remoteMac []byte, h prf.HashFunc) (*CBC, error) {
+	writeBlock, err := aes.NewCipher(localKey)
+	if err != nil {
+		return nil, err
+	}
+
+	readBlock, err := aes.NewCipher(remoteKey)
+	if err != nil {
+		return nil, err
+	}
+
+	return &CBC{
+		writeCBC: cipher.NewCBCEncrypter(writeBlock, localWriteIV).(cbcMode),
+		writeMac: localMac,
+
+		readCBC: cipher.NewCBCDecrypter(readBlock, remoteWriteIV).(cbcMode),
+		readMac: remoteMac,
+		h:       h,
+	}, nil
+}
+
+// Encrypt encrypt a DTLS RecordLayer message
+func (c *CBC) Encrypt(pkt *recordlayer.RecordLayer, raw []byte) ([]byte, error) {
+	payload := raw[recordlayer.HeaderSize:]
+	raw = raw[:recordlayer.HeaderSize]
+	blockSize := c.writeCBC.BlockSize()
+
+	// Generate + Append MAC
+	h := pkt.Header
+
+	MAC, err := c.hmac(h.Epoch, h.SequenceNumber, h.ContentType, h.Version, payload, c.writeMac, c.h)
+	if err != nil {
+		return nil, err
+	}
+	payload = append(payload, MAC...)
+
+	// Generate + Append padding
+	padding := make([]byte, blockSize-len(payload)%blockSize)
+	paddingLen := len(padding)
+	for i := 0; i < paddingLen; i++ {
+		padding[i] = byte(paddingLen - 1)
+	}
+	payload = append(payload, padding...)
+
+	// Generate IV
+	iv := make([]byte, blockSize)
+	if _, err := rand.Read(iv); err != nil {
+		return nil, err
+	}
+
+	// Set IV + Encrypt + Prepend IV
+	c.writeCBC.SetIV(iv)
+	c.writeCBC.CryptBlocks(payload, payload)
+	payload = append(iv, payload...)
+
+	// Prepend unencrypte header with encrypted payload
+	raw = append(raw, payload...)
+
+	// Update recordLayer size to include IV+MAC+Padding
+	binary.BigEndian.PutUint16(raw[recordlayer.HeaderSize-2:], uint16(len(raw)-recordlayer.HeaderSize))
+
+	return raw, nil
+}
+
+// Decrypt decrypts a DTLS RecordLayer message
+func (c *CBC) Decrypt(in []byte) ([]byte, error) {
+	body := in[recordlayer.HeaderSize:]
+	blockSize := c.readCBC.BlockSize()
+	mac := c.h()
+
+	var h recordlayer.Header
+	err := h.Unmarshal(in)
+	switch {
+	case err != nil:
+		return nil, err
+	case h.ContentType == protocol.ContentTypeChangeCipherSpec:
+		// Nothing to encrypt with ChangeCipherSpec
+		return in, nil
+	case len(body)%blockSize != 0 || len(body) < blockSize+util.Max(mac.Size()+1, blockSize):
+		return nil, errNotEnoughRoomForNonce
+	}
+
+	// Set + remove per record IV
+	c.readCBC.SetIV(body[:blockSize])
+	body = body[blockSize:]
+
+	// Decrypt
+	c.readCBC.CryptBlocks(body, body)
+
+	// Padding+MAC needs to be checked in constant time
+	// Otherwise we reveal information about the level of correctness
+	paddingLen, paddingGood := examinePadding(body)
+	if paddingGood != 255 {
+		return nil, errInvalidMAC
+	}
+
+	macSize := mac.Size()
+	if len(body) < macSize {
+		return nil, errInvalidMAC
+	}
+
+	dataEnd := len(body) - macSize - paddingLen
+
+	expectedMAC := body[dataEnd : dataEnd+macSize]
+	actualMAC, err := c.hmac(h.Epoch, h.SequenceNumber, h.ContentType, h.Version, body[:dataEnd], c.readMac, c.h)
+
+	// Compute Local MAC and compare
+	if err != nil || !hmac.Equal(actualMAC, expectedMAC) {
+		return nil, errInvalidMAC
+	}
+
+	return append(in[:recordlayer.HeaderSize], body[:dataEnd]...), nil
+}
+
+func (c *CBC) hmac(epoch uint16, sequenceNumber uint64, contentType protocol.ContentType, protocolVersion protocol.Version, payload []byte, key []byte, hf func() hash.Hash) ([]byte, error) {
+	h := hmac.New(hf, key)
+
+	msg := make([]byte, 13)
+
+	binary.BigEndian.PutUint16(msg, epoch)
+	util.PutBigEndianUint48(msg[2:], sequenceNumber)
+	msg[8] = byte(contentType)
+	msg[9] = protocolVersion.Major
+	msg[10] = protocolVersion.Minor
+	binary.BigEndian.PutUint16(msg[11:], uint16(len(payload)))
+
+	if _, err := h.Write(msg); err != nil {
+		return nil, err
+	} else if _, err := h.Write(payload); err != nil {
+		return nil, err
+	}
+
+	return h.Sum(nil), nil
+}