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package cryptfs
import (
"errors"
"io/ioutil"
"encoding/json"
)
import "os"
const (
// Changing this string breaks backward compatability
testBlockData = "gocryptfs test block"
// The dot "." is not used in base64url (RFC4648), hence
// we can never clash with an encrypted file.
ConfDefaultName = "gocryptfs.conf"
)
type confFile struct {
// File the config is saved in. Lowercase => not exported to JSON.
filename string
// Unencrypted AES key
Key [16]byte
// GCM ciphertext with auth tag to verify the key is correct
TestBlock []byte
}
// CreateConfFile - create a new config file with "key" and write to "filename"
func CreateConfFile(filename string, key [16]byte) error {
var cf confFile
cf.filename = filename
cf.Key = key
// Generate test block
cfs := NewCryptFS(cf.Key, false)
cf.TestBlock = cfs.EncryptBlock([]byte(testBlockData))
// Write file to disk
err := cf.WriteFile()
return err
}
// LoadConfFile - read config file from disk and verify the key using the
// embedded TestBlock
func LoadConfFile(filename string) (*confFile, error) {
// Read from disk
js, err := ioutil.ReadFile(filename)
if err != nil {
return nil, err
}
var cf confFile
err = json.Unmarshal(js, &cf)
if err != nil {
return nil, err
}
cf.filename = filename
// Try to decrypt the test block to see if the key is correct
//
// Speed does not matter here. Use built-in crypto.
cfs := NewCryptFS(cf.Key, false)
d, err := cfs.DecryptBlock(cf.TestBlock)
if err != nil {
return nil, err
}
ds := string(d)
if ds != testBlockData {
return nil, errors.New("Invalid test block content: " + ds)
}
return &cf, nil
}
// WriteFile - write out config in JSON format to file "filename.tmp"
// then rename over "filename"
func (cf *confFile) WriteFile() error {
tmp := cf.filename + ".tmp"
fd, err := os.Create(tmp)
if err != nil {
return err
}
js, err := json.Marshal(cf)
if err != nil {
return err
}
_, err = fd.Write(js)
if err != nil {
return err
}
err = fd.Sync()
if err != nil {
return err
}
err = fd.Close()
if err != nil {
return err
}
err = os.Rename(tmp, cf.filename)
if err != nil {
return err
}
return nil
}
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