forked from mirror/zip
Tidy up error handling and comments
This commit is contained in:
alexmullins
parent
34bcc3949b
commit
fcc3c52422
55
crypto.go
55
crypto.go
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@ -41,7 +41,6 @@ func aesKeyLen(strength byte) int {
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// Encryption/Decryption Errors
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var (
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ErrEncryption = errors.New("zip: encryption error")
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ErrDecryption = errors.New("zip: decryption error")
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ErrPassword = errors.New("zip: invalid password")
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ErrAuthentication = errors.New("zip: authentication failed")
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@ -188,16 +187,16 @@ func (a *authReader) Read(p []byte) (int, error) {
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a.err = err
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}
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// write any data to mac
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nn, err := a.mac.Write(p[:n])
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if nn != n || err != nil {
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a.err = io.ErrUnexpectedEOF
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_, err = a.mac.Write(p[:n])
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if err != nil {
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a.err = err
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return n, a.err
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}
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if end {
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ab := new(bytes.Buffer)
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_, err = io.Copy(ab, a.adata)
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if err != nil || ab.Len() != 10 {
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a.err = io.ErrUnexpectedEOF
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a.err = ErrDecryption
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return n, a.err
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}
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if !a.checkAuthentication(ab.Bytes()) {
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@ -223,18 +222,21 @@ func (a *bufferedAuthReader) Read(b []byte) (int, error) {
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if !a.auth {
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_, err := io.Copy(a.buf, a.data)
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if err != nil {
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a.err = io.ErrUnexpectedEOF
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a.err = err
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return 0, a.err
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}
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ab := new(bytes.Buffer) // remove this buffer and io.Copy to mac
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ab := new(bytes.Buffer)
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nn, err := io.Copy(ab, a.adata)
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if err != nil || nn != 10 {
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a.err = io.ErrUnexpectedEOF
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if err != nil {
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a.err = err
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return 0, a.err
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} else if nn != 10 {
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a.err = ErrDecryption
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return 0, a.err
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}
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mn, err := a.mac.Write(a.buf.Bytes())
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if mn != a.buf.Len() || err != nil {
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a.err = io.ErrUnexpectedEOF
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_, err = a.mac.Write(a.buf.Bytes())
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if err != nil {
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a.err = err
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return 0, a.err
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}
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if !a.checkAuthentication(ab.Bytes()) {
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@ -254,7 +256,6 @@ func (a *authReader) checkAuthentication(authcode []byte) bool {
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expectedAuthCode := a.mac.Sum(nil)
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// Truncate at the first 10 bytes
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expectedAuthCode = expectedAuthCode[:10]
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// Change to use crypto/subtle for constant time comparison
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a.auth = subtle.ConstantTimeCompare(expectedAuthCode, authcode) > 0
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return a.auth
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}
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@ -280,20 +281,18 @@ func newDecryptionReader(r *io.SectionReader, f *File) (io.Reader, error) {
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if saltLen == 0 {
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return nil, ErrDecryption
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}
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// grab the salt, pwvv, data, and authcode
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// grab the salt and pwvv
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saltpwvv := make([]byte, saltLen+2)
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if _, err := r.Read(saltpwvv); err != nil {
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return nil, err
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}
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salt := saltpwvv[:saltLen]
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pwvv := saltpwvv[saltLen : saltLen+2]
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// generate keys
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// generate keys only if we have a password
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if f.password == nil {
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return nil, ErrPassword
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}
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decKey, authKey, pwv := generateKeys(f.password(), salt, keyLen)
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// check password verifier (pwv)
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// Change to use crypto/subtle for constant time comparison
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if !checkPasswordVerification(pwv, pwvv) {
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return nil, ErrPassword
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}
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@ -306,9 +305,7 @@ func newDecryptionReader(r *io.SectionReader, f *File) (io.Reader, error) {
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data := io.NewSectionReader(r, dataOff, dataLen)
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authOff := dataOff + dataLen
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authcode := io.NewSectionReader(r, authOff, 10)
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// setup auth reader, (buffered)/streaming
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ar := newAuthReader(authKey, data, authcode, f.DeferAuth)
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// return decryption reader
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dr := decryptStream(decKey, ar)
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if dr == nil {
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return nil, ErrDecryption
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@ -342,12 +339,12 @@ func (aw *authWriter) Write(p []byte) (int, error) {
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// writes out the salt, pwv, and then the encrypted file data
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type encryptionWriter struct {
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pwv []byte // password verification code to be written
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salt []byte // salt to be written
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pwv []byte
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salt []byte
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w io.Writer // where to write the salt + pwv
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es io.Writer // where to write plaintext
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first bool // first write
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err error // last error
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err error
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}
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func (ew *encryptionWriter) Write(p []byte) (int, error) {
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@ -372,7 +369,7 @@ func (ew *encryptionWriter) Write(p []byte) (int, error) {
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func encryptStream(key []byte, w io.Writer) (io.Writer, error) {
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block, err := aes.NewCipher(key)
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if err != nil {
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return nil, errors.New("zip: couldn't create AES cipher")
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return nil, err
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}
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stream := newWinZipCTR(block)
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writer := &cipher.StreamWriter{S: stream, W: w}
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@ -382,13 +379,13 @@ func encryptStream(key []byte, w io.Writer) (io.Writer, error) {
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// newEncryptionWriter returns an io.Writer that when written to, 1. writes
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// out the salt, 2. writes out pwv, and 3. writes out authenticated, encrypted
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// data. The authcode will be written out in fileWriter.close().
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func newEncryptionWriter(w io.Writer, fh *FileHeader, fw *fileWriter) (io.Writer, error) {
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func newEncryptionWriter(w io.Writer, password passwordFn, fw *fileWriter) (io.Writer, error) {
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var salt [16]byte
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_, err := rand.Read(salt[:])
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if err != nil {
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return nil, errors.New("zip: unable to generate random salt")
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}
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ekey, akey, pwv := generateKeys(fh.password(), salt[:], aes256)
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ekey, akey, pwv := generateKeys(password(), salt[:], aes256)
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fw.hmac = hmac.New(sha1.New, akey)
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aw := &authWriter{
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hmac: fw.hmac,
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@ -450,9 +447,11 @@ func (h *FileHeader) SetPassword(password string) {
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// as a byte slice
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type passwordFn func() []byte
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// Encrypt is similar to Create except that it will encrypt the file contents
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// using AES-256 with the given password. Must follow all the same constraints
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// as Create.
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// Encrypt adds a file to the zip file using the provided name.
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// It returns a Writer to which the file contents should be written. File
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// contents will be encrypted with AES-256 using the given password. The
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// file's contents must be written to the io.Writer before the next call
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// to Create, CreateHeader, or Close.
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func (w *Writer) Encrypt(name string, password string) (io.Writer, error) {
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fh := &FileHeader{
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Name: name,
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@ -232,9 +232,9 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
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// we have a password and need to encrypt.
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fh.writeWinZipExtra()
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fh.Method = 99 // ok to change, we've gotten the comp and wrote extra
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ew, err := newEncryptionWriter(sw, fh, fw)
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ew, err := newEncryptionWriter(sw, fh.password, fw)
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if err != nil {
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return nil, errors.New("zip: unable to create an encryption writer")
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return nil, err
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}
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sw = ew
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}
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