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package ciphersuite
import (
"crypto/aes"
"crypto/rand"
"encoding/binary"
"fmt"
"github.com/pion/dtls/v2/pkg/crypto/ccm"
"github.com/pion/dtls/v2/pkg/protocol"
"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
)
// CCMTagLen is the length of Authentication Tag
type CCMTagLen int
// CCM Enums
const (
CCMTagLength8 CCMTagLen = 8
CCMTagLength CCMTagLen = 16
ccmNonceLength = 12
)
// CCM Provides an API to Encrypt/Decrypt DTLS 1.2 Packets
type CCM struct {
localCCM, remoteCCM ccm.CCM
localWriteIV, remoteWriteIV []byte
tagLen CCMTagLen
}
// NewCCM creates a DTLS GCM Cipher
func NewCCM(tagLen CCMTagLen, localKey, localWriteIV, remoteKey, remoteWriteIV []byte) (*CCM, error) {
localBlock, err := aes.NewCipher(localKey)
if err != nil {
return nil, err
}
localCCM, err := ccm.NewCCM(localBlock, int(tagLen), ccmNonceLength)
if err != nil {
return nil, err
}
remoteBlock, err := aes.NewCipher(remoteKey)
if err != nil {
return nil, err
}
remoteCCM, err := ccm.NewCCM(remoteBlock, int(tagLen), ccmNonceLength)
if err != nil {
return nil, err
}
return &CCM{
localCCM: localCCM,
localWriteIV: localWriteIV,
remoteCCM: remoteCCM,
remoteWriteIV: remoteWriteIV,
tagLen: tagLen,
}, nil
}
// Encrypt encrypt a DTLS RecordLayer message
func (c *CCM) Encrypt(pkt *recordlayer.RecordLayer, raw []byte) ([]byte, error) {
payload := raw[recordlayer.HeaderSize:]
raw = raw[:recordlayer.HeaderSize]
nonce := append(append([]byte{}, c.localWriteIV[:4]...), make([]byte, 8)...)
if _, err := rand.Read(nonce[4:]); err != nil {
return nil, err
}
additionalData := generateAEADAdditionalData(&pkt.Header, len(payload))
encryptedPayload := c.localCCM.Seal(nil, nonce, payload, additionalData)
encryptedPayload = append(nonce[4:], encryptedPayload...)
raw = append(raw, encryptedPayload...)
// Update recordLayer size to include explicit nonce
binary.BigEndian.PutUint16(raw[recordlayer.HeaderSize-2:], uint16(len(raw)-recordlayer.HeaderSize))
return raw, nil
}
// Decrypt decrypts a DTLS RecordLayer message
func (c *CCM) 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 := append(append([]byte{}, c.remoteWriteIV[:4]...), in[recordlayer.HeaderSize:recordlayer.HeaderSize+8]...)
out := in[recordlayer.HeaderSize+8:]
additionalData := generateAEADAdditionalData(&h, len(out)-int(c.tagLen))
out, err = c.remoteCCM.Open(out[:0], nonce, out, additionalData)
if err != nil {
return nil, fmt.Errorf("%w: %v", errDecryptPacket, err)
}
return append(in[:recordlayer.HeaderSize], out...), nil
}
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