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Diffstat (limited to 'cryptfs/config_file.go')
-rw-r--r--cryptfs/config_file.go104
1 files changed, 104 insertions, 0 deletions
diff --git a/cryptfs/config_file.go b/cryptfs/config_file.go
new file mode 100644
index 0000000..752ed09
--- /dev/null
+++ b/cryptfs/config_file.go
@@ -0,0 +1,104 @@
+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
+}