forked from canhlinh/hlsdl
/
decrypt.go
103 lines (87 loc) · 1.98 KB
/
decrypt.go
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package hlsdl
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"encoding/binary"
"errors"
"io/ioutil"
"os"
)
const (
syncByte = uint8(71) //0x47
)
func decryptAES128(crypted, key, iv []byte) ([]byte, error) {
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
blockSize := block.BlockSize()
blockMode := cipher.NewCBCDecrypter(block, iv[:blockSize])
origData := make([]byte, len(crypted))
blockMode.CryptBlocks(origData, crypted)
origData = pkcs5UnPadding(origData)
return origData, nil
}
func pkcs5Padding(cipherText []byte, blockSize int) []byte {
padding := blockSize - len(cipherText)%blockSize
padText := bytes.Repeat([]byte{byte(padding)}, padding)
return append(cipherText, padText...)
}
func pkcs5UnPadding(origData []byte) []byte {
length := len(origData)
unPadding := int(origData[length-1])
return origData[:(length - unPadding)]
}
// Decrypt descryps a segment
func (hlsDl *HlsDl) decrypt(segment *Segment) ([]byte, error) {
file, err := os.Open(segment.Path)
if err != nil {
return nil, err
}
defer file.Close()
data, err := ioutil.ReadAll(file)
if err != nil {
return nil, err
}
if segment.Key != nil {
key, iv, err := hlsDl.getKey(segment)
if err != nil {
return nil, err
}
data, err = decryptAES128(data, key, iv)
if err != nil {
return nil, err
}
}
for j := 0; j < len(data); j++ {
if data[j] == syncByte {
data = data[j:]
break
}
}
return data, nil
}
func (hlsDl *HlsDl) getKey(segment *Segment) (key []byte, iv []byte, err error) {
res, err := hlsDl.client.Get(segment.Key.URI)
if err != nil {
return nil, nil, err
}
if res.StatusCode != 200 {
return nil, nil, errors.New("Failed to get descryption key")
}
key, err = ioutil.ReadAll(res.Body)
if err != nil {
return nil, nil, err
}
iv = []byte(segment.Key.IV)
if len(iv) == 0 {
iv = defaultIV(segment.SeqId)
}
return
}
func defaultIV(seqID uint64) []byte {
buf := make([]byte, 16)
binary.BigEndian.PutUint64(buf[8:], seqID)
return buf
}