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support ECMA-376 document standard encryption, ref #199

This commit is contained in:
xuri 2020-09-02 23:14:19 +08:00
parent 4177c1585e
commit 98f1a69903
No known key found for this signature in database
GPG Key ID: BA5E5BB1C948EDF7
6 changed files with 209 additions and 30 deletions
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221
encrypt.go → crypt.go
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@ -20,6 +20,7 @@ import (
"encoding/base64"
"encoding/binary"
"encoding/xml"
"errors"
"hash"
"strings"
@ -33,6 +34,7 @@ var (
blockKey = []byte{0x14, 0x6e, 0x0b, 0xe7, 0xab, 0xac, 0xd0, 0xd6} // Block keys used for encryption
packageOffset = 8 // First 8 bytes are the size of the stream
packageEncryptionChunkSize = 4096
iterCount = 50000
cryptoIdentifier = []byte{ // checking protect workbook by [MS-OFFCRYPTO] - v20181211 3.1 FeatureIdentifier
0x3c, 0x00, 0x00, 0x00, 0x4d, 0x00, 0x69, 0x00, 0x63, 0x00, 0x72, 0x00, 0x6f, 0x00, 0x73, 0x00,
0x6f, 0x00, 0x66, 0x00, 0x74, 0x00, 0x2e, 0x00, 0x43, 0x00, 0x6f, 0x00, 0x6e, 0x00, 0x74, 0x00,
@ -40,6 +42,9 @@ var (
0x74, 0x00, 0x61, 0x00, 0x53, 0x00, 0x70, 0x00, 0x61, 0x00, 0x63, 0x00, 0x65, 0x00, 0x73, 0x00,
0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
}
oleIdentifier = []byte{
0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1,
}
)
// Encryption specifies the encryption structure, streams, and storages are
@ -93,37 +98,56 @@ type EncryptedKey struct {
KeyData
}
// Decrypt API decrypt the CFB file format with Agile Encryption. Support
// cryptographic algorithm: MD4, MD5, RIPEMD-160, SHA1, SHA256, SHA384 and
// SHA512.
// StandardEncryptionHeader structure is used by ECMA-376 document encryption
// [ECMA-376] and Office binary document RC4 CryptoAPI encryption, to specify
// encryption properties for an encrypted stream.
type StandardEncryptionHeader struct {
Flags uint32
SizeExtra uint32
AlgID uint32
AlgIDHash uint32
KeySize uint32
ProviderType uint32
Reserved1 uint32
Reserved2 uint32
CspName string
}
// StandardEncryptionVerifier structure is used by Office Binary Document RC4
// CryptoAPI Encryption and ECMA-376 Document Encryption. Every usage of this
// structure MUST specify the hashing algorithm and encryption algorithm used
// in the EncryptionVerifier structure.
type StandardEncryptionVerifier struct {
SaltSize uint32
Salt []byte
EncryptedVerifier []byte
VerifierHashSize uint32
EncryptedVerifierHash []byte
}
// Decrypt API decrypt the CFB file format with ECMA-376 agile encryption and
// standard encryption. Support cryptographic algorithm: MD4, MD5, RIPEMD-160,
// SHA1, SHA256, SHA384 and SHA512 currently.
func Decrypt(raw []byte, opt *Options) (packageBuf []byte, err error) {
doc, err := mscfb.New(bytes.NewReader(raw))
if err != nil {
return
}
encryptionInfoBuf, encryptedPackageBuf := extractPart(doc)
var encryptionInfo Encryption
if encryptionInfo, err = parseEncryptionInfo(encryptionInfoBuf[8:]); err != nil {
mechanism, err := encryptionMechanism(encryptionInfoBuf)
if err != nil || mechanism == "extensible" {
return
}
// Convert the password into an encryption key.
key, err := convertPasswdToKey(opt.Password, encryptionInfo)
if err != nil {
return
switch mechanism {
case "agile":
return agileDecrypt(encryptionInfoBuf, encryptedPackageBuf, opt)
case "standard":
return standardDecrypt(encryptionInfoBuf, encryptedPackageBuf, opt)
default:
err = errors.New("unsupport encryption mechanism")
break
}
// Use the key to decrypt the package key.
encryptedKey := encryptionInfo.KeyEncryptors.KeyEncryptor[0].EncryptedKey
saltValue, err := base64.StdEncoding.DecodeString(encryptedKey.SaltValue)
if err != nil {
return
}
encryptedKeyValue, err := base64.StdEncoding.DecodeString(encryptedKey.EncryptedKeyValue)
if err != nil {
return
}
packageKey, err := crypt(false, encryptedKey.CipherAlgorithm, encryptedKey.CipherChaining, key, saltValue, encryptedKeyValue)
// Use the package key to decrypt the package.
return cryptPackage(false, packageKey, encryptedPackageBuf, encryptionInfo)
return
}
// extractPart extract data from storage by specified part name.
@ -149,6 +173,159 @@ func extractPart(doc *mscfb.Reader) (encryptionInfoBuf, encryptedPackageBuf []by
return
}
// encryptionMechanism parse password-protected documents created mechanism.
func encryptionMechanism(buffer []byte) (mechanism string, err error) {
if len(buffer) < 4 {
err = errors.New("unknown encryption mechanism")
return
}
versionMajor, versionMinor := binary.LittleEndian.Uint16(buffer[0:2]), binary.LittleEndian.Uint16(buffer[2:4])
if versionMajor == 4 && versionMinor == 4 {
mechanism = "agile"
return
} else if (2 <= versionMajor && versionMajor <= 4) && versionMinor == 2 {
mechanism = "standard"
return
} else if (versionMajor == 3 || versionMajor == 4) && versionMinor == 3 {
mechanism = "extensible"
}
err = errors.New("unsupport encryption mechanism")
return
}
// ECMA-376 Standard Encryption
// standardDecrypt decrypt the CFB file format with ECMA-376 standard encryption.
func standardDecrypt(encryptionInfoBuf, encryptedPackageBuf []byte, opt *Options) ([]byte, error) {
encryptionHeaderSize := binary.LittleEndian.Uint32(encryptionInfoBuf[8:12])
block := encryptionInfoBuf[12 : 12+encryptionHeaderSize]
header := StandardEncryptionHeader{
Flags: binary.LittleEndian.Uint32(block[:4]),
SizeExtra: binary.LittleEndian.Uint32(block[4:8]),
AlgID: binary.LittleEndian.Uint32(block[8:12]),
AlgIDHash: binary.LittleEndian.Uint32(block[12:16]),
KeySize: binary.LittleEndian.Uint32(block[16:20]),
ProviderType: binary.LittleEndian.Uint32(block[20:24]),
Reserved1: binary.LittleEndian.Uint32(block[24:28]),
Reserved2: binary.LittleEndian.Uint32(block[28:32]),
CspName: string(block[32:]),
}
block = encryptionInfoBuf[12+encryptionHeaderSize:]
algIDMap := map[uint32]string{
0x0000660E: "AES-128",
0x0000660F: "AES-192",
0x00006610: "AES-256",
}
algorithm := "AES"
_, ok := algIDMap[header.AlgID]
if !ok {
algorithm = "RC4"
}
verifier := standardEncryptionVerifier(algorithm, block)
secretKey, err := standardConvertPasswdToKey(header, verifier, opt)
if err != nil {
return nil, err
}
// decrypted data
x := encryptedPackageBuf[8:]
blob, err := aes.NewCipher(secretKey)
if err != nil {
return nil, err
}
decrypted := make([]byte, len(x))
size := 16
for bs, be := 0, size; bs < len(x); bs, be = bs+size, be+size {
blob.Decrypt(decrypted[bs:be], x[bs:be])
}
return decrypted, err
}
// standardEncryptionVerifier extract ECMA-376 standard encryption verifier.
func standardEncryptionVerifier(algorithm string, blob []byte) StandardEncryptionVerifier {
verifier := StandardEncryptionVerifier{
SaltSize: binary.LittleEndian.Uint32(blob[:4]),
Salt: blob[4:20],
EncryptedVerifier: blob[20:36],
VerifierHashSize: binary.LittleEndian.Uint32(blob[36:40]),
}
if algorithm == "RC4" {
verifier.EncryptedVerifierHash = blob[40:60]
} else if algorithm == "AES" {
verifier.EncryptedVerifierHash = blob[40:72]
}
return verifier
}
// standardConvertPasswdToKey generate intermediate key from given password.
func standardConvertPasswdToKey(header StandardEncryptionHeader, verifier StandardEncryptionVerifier, opt *Options) ([]byte, error) {
encoder := unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM).NewEncoder()
passwordBuffer, err := encoder.Bytes([]byte(opt.Password))
if err != nil {
return nil, err
}
key := hashing("sha1", verifier.Salt, passwordBuffer)
for i := 0; i < iterCount; i++ {
iterator := createUInt32LEBuffer(i)
key = hashing("sha1", iterator, key)
}
var block int
hfinal := hashing("sha1", key, createUInt32LEBuffer(block))
cbRequiredKeyLength := int(header.KeySize) / 8
cbHash := sha1.Size
buf1 := bytes.Repeat([]byte{0x36}, 64)
buf1 = append(standardXORBytes(hfinal, buf1[:cbHash]), buf1[cbHash:]...)
x1 := hashing("sha1", buf1)
buf2 := bytes.Repeat([]byte{0x5c}, 64)
buf2 = append(standardXORBytes(hfinal, buf2[:cbHash]), buf2[cbHash:]...)
x2 := hashing("sha1", buf2)
x3 := append(x1, x2...)
keyDerived := x3[:cbRequiredKeyLength]
return keyDerived, err
}
// standardXORBytes perform XOR operations for two bytes slice.
func standardXORBytes(a, b []byte) []byte {
r := make([][2]byte, len(a), len(a))
for i, e := range a {
r[i] = [2]byte{e, b[i]}
}
buf := make([]byte, len(a))
for p, q := range r {
buf[p] = q[0] ^ q[1]
}
return buf
}
// ECMA-376 Agile Encryption
// agileDecrypt decrypt the CFB file format with ECMA-376 agile encryption.
// Support cryptographic algorithm: MD4, MD5, RIPEMD-160, SHA1, SHA256, SHA384
// and SHA512.
func agileDecrypt(encryptionInfoBuf, encryptedPackageBuf []byte, opt *Options) (packageBuf []byte, err error) {
var encryptionInfo Encryption
if encryptionInfo, err = parseEncryptionInfo(encryptionInfoBuf[8:]); err != nil {
return
}
// Convert the password into an encryption key.
key, err := convertPasswdToKey(opt.Password, encryptionInfo)
if err != nil {
return
}
// Use the key to decrypt the package key.
encryptedKey := encryptionInfo.KeyEncryptors.KeyEncryptor[0].EncryptedKey
saltValue, err := base64.StdEncoding.DecodeString(encryptedKey.SaltValue)
if err != nil {
return
}
encryptedKeyValue, err := base64.StdEncoding.DecodeString(encryptedKey.EncryptedKeyValue)
if err != nil {
return
}
packageKey, err := crypt(false, encryptedKey.CipherAlgorithm, encryptedKey.CipherChaining, key, saltValue, encryptedKeyValue)
// Use the package key to decrypt the package.
return cryptPackage(false, packageKey, encryptedPackageBuf, encryptionInfo)
}
// convertPasswdToKey convert the password into an encryption key.
func convertPasswdToKey(passwd string, encryption Encryption) (key []byte, err error) {
var b bytes.Buffer

3
drawing.go
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@ -59,10 +59,7 @@ func (f *File) prepareChartSheetDrawing(xlsx *xlsxChartsheet, drawingID int, she
func (f *File) addChart(formatSet *formatChart, comboCharts []*formatChart) {
count := f.countCharts()
xlsxChartSpace := xlsxChartSpace{
XMLNSc: NameSpaceDrawingMLChart.Value,
XMLNSa: NameSpaceDrawingML.Value,
XMLNSr: SourceRelationship.Value,
XMLNSc16r2: SourceRelationshipChart201506.Value,
Date1904: &attrValBool{Val: boolPtr(false)},
Lang: &attrValString{Val: stringPtr("en-US")},
RoundedCorners: &attrValBool{Val: boolPtr(false)},

2
excelize.go
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@ -111,7 +111,7 @@ func OpenReader(r io.Reader, opt ...Options) (*File, error) {
if err != nil {
return nil, err
}
if bytes.Contains(b, cryptoIdentifier) {
if bytes.Contains(b, oleIdentifier) {
var option Options
for _, o := range opt {
option = o

10
excelize_test.go
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@ -201,15 +201,23 @@ func TestCharsetTranscoder(t *testing.T) {
func TestOpenReader(t *testing.T) {
_, err := OpenReader(strings.NewReader(""))
assert.EqualError(t, err, "zip: not a valid zip file")
_, err = OpenReader(bytes.NewReader(cryptoIdentifier))
_, err = OpenReader(bytes.NewReader(oleIdentifier))
assert.EqualError(t, err, "decrypted file failed")
// Test open password protected spreadsheet created by Microsoft Office Excel 2010.
f, err := OpenFile(filepath.Join("test", "encryptSHA1.xlsx"), Options{Password: "password"})
assert.NoError(t, err)
val, err := f.GetCellValue("Sheet1", "A1")
assert.NoError(t, err)
assert.Equal(t, "SECRET", val)
// Test open password protected spreadsheet created by LibreOffice 7.0.0.3.
f, err = OpenFile(filepath.Join("test", "encryptAES.xlsx"), Options{Password: "password"})
assert.NoError(t, err)
val, err = f.GetCellValue("Sheet1", "A1")
assert.NoError(t, err)
assert.Equal(t, "SECRET", val)
// Test unexpected EOF.
var b bytes.Buffer
w := gzip.NewWriter(&b)

BIN
test/encryptAES.xlsx Normal file
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Binary file not shown.

3
xmlChart.go
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@ -18,10 +18,7 @@ import "encoding/xml"
// charts, pie charts, scatter charts, or other types of charts.
type xlsxChartSpace struct {
XMLName xml.Name `xml:"http://schemas.openxmlformats.org/drawingml/2006/chart chartSpace"`
XMLNSc string `xml:"xmlns:c,attr"`
XMLNSa string `xml:"xmlns:a,attr"`
XMLNSr string `xml:"xmlns:r,attr"`
XMLNSc16r2 string `xml:"xmlns:c16r2,attr"`
Date1904 *attrValBool `xml:"date1904"`
Lang *attrValString `xml:"lang"`
RoundedCorners *attrValBool `xml:"roundedCorners"`