添加 github.com/pion/dtls 代码

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

@@ -0,0 +1,100 @@
+package ciphersuite
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+
+	"github.com/pion/dtls/v2/pkg/protocol"
+	"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
+)
+
+const (
+	gcmTagLength   = 16
+	gcmNonceLength = 12
+)
+
+// GCM Provides an API to Encrypt/Decrypt DTLS 1.2 Packets
+type GCM struct {
+	localGCM, remoteGCM         cipher.AEAD
+	localWriteIV, remoteWriteIV []byte
+}
+
+// NewGCM creates a DTLS GCM Cipher
+func NewGCM(localKey, localWriteIV, remoteKey, remoteWriteIV []byte) (*GCM, error) {
+	localBlock, err := aes.NewCipher(localKey)
+	if err != nil {
+		return nil, err
+	}
+	localGCM, err := cipher.NewGCM(localBlock)
+	if err != nil {
+		return nil, err
+	}
+
+	remoteBlock, err := aes.NewCipher(remoteKey)
+	if err != nil {
+		return nil, err
+	}
+	remoteGCM, err := cipher.NewGCM(remoteBlock)
+	if err != nil {
+		return nil, err
+	}
+
+	return &GCM{
+		localGCM:      localGCM,
+		localWriteIV:  localWriteIV,
+		remoteGCM:     remoteGCM,
+		remoteWriteIV: remoteWriteIV,
+	}, nil
+}
+
+// Encrypt encrypt a DTLS RecordLayer message
+func (g *GCM) Encrypt(pkt *recordlayer.RecordLayer, raw []byte) ([]byte, error) {
+	payload := raw[recordlayer.HeaderSize:]
+	raw = raw[:recordlayer.HeaderSize]
+
+	nonce := make([]byte, gcmNonceLength)
+	copy(nonce, g.localWriteIV[:4])
+	if _, err := rand.Read(nonce[4:]); err != nil {
+		return nil, err
+	}
+
+	additionalData := generateAEADAdditionalData(&pkt.Header, len(payload))
+	encryptedPayload := g.localGCM.Seal(nil, nonce, payload, additionalData)
+	r := make([]byte, len(raw)+len(nonce[4:])+len(encryptedPayload))
+	copy(r, raw)
+	copy(r[len(raw):], nonce[4:])
+	copy(r[len(raw)+len(nonce[4:]):], encryptedPayload)
+
+	// Update recordLayer size to include explicit nonce
+	binary.BigEndian.PutUint16(r[recordlayer.HeaderSize-2:], uint16(len(r)-recordlayer.HeaderSize))
+	return r, nil
+}
+
+// Decrypt decrypts a DTLS RecordLayer message
+func (g *GCM) Decrypt(in []byte) ([]byte, error) {
+	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(in) <= (8 + recordlayer.HeaderSize):
+		return nil, errNotEnoughRoomForNonce
+	}
+
+	nonce := make([]byte, 0, gcmNonceLength)
+	nonce = append(append(nonce, g.remoteWriteIV[:4]...), in[recordlayer.HeaderSize:recordlayer.HeaderSize+8]...)
+	out := in[recordlayer.HeaderSize+8:]
+
+	additionalData := generateAEADAdditionalData(&h, len(out)-gcmTagLength)
+	out, err = g.remoteGCM.Open(out[:0], nonce, out, additionalData)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %v", errDecryptPacket, err)
+	}
+	return append(in[:recordlayer.HeaderSize], out...), nil
+}