1 files changed, 195 insertions, 0 deletions
diff --git a/internal/configfile/config_file.go b/internal/configfile/config_file.go
new file mode 100644
index 0000000..0128acc
--- /dev/null
+++ b/internal/configfile/config_file.go
@@ -0,0 +1,195 @@
+package configfile
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+
+	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
+)
+import "os"
+
+const (
+	// 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 to. Not exported to JSON.
+	filename string
+	// Encrypted AES key, unlocked using a password hashed with scrypt
+	EncryptedKey []byte
+	// Stores parameters for scrypt hashing (key derivation)
+	ScryptObject scryptKdf
+	// The On-Disk-Format version this filesystem uses
+	Version uint16
+	// List of feature flags this filesystem has enabled.
+	// If gocryptfs encounters a feature flag it does not support, it will refuse
+	// mounting. This mechanism is analogous to the ext4 feature flags that are
+	// stored in the superblock.
+	FeatureFlags []string
+}
+
+// CreateConfFile - create a new config with a random key encrypted with
+// "password" and write it to "filename".
+// Uses scrypt with cost parameter logN.
+func CreateConfFile(filename string, password string, plaintextNames bool, logN int) error {
+	var cf ConfFile
+	cf.filename = filename
+	cf.Version = contentenc.CurrentVersion
+
+	// Generate new random master key
+	key := cryptocore.RandBytes(cryptocore.KeyLen)
+
+	// Encrypt it using the password
+	// This sets ScryptObject and EncryptedKey
+	cf.EncryptKey(key, password, logN)
+
+	// Set feature flags
+	cf.FeatureFlags = append(cf.FeatureFlags, FlagGCMIV128)
+	if plaintextNames {
+		cf.FeatureFlags = append(cf.FeatureFlags, FlagPlaintextNames)
+	} else {
+		cf.FeatureFlags = append(cf.FeatureFlags, FlagDirIV)
+		cf.FeatureFlags = append(cf.FeatureFlags, FlagEMENames)
+	}
+
+	// Write file to disk
+	return cf.WriteFile()
+}
+
+// LoadConfFile - read config file from disk and decrypt the
+// contained key using password.
+//
+// Returns the decrypted key and the ConfFile object
+func LoadConfFile(filename string, password string) ([]byte, *ConfFile, error) {
+	var cf ConfFile
+	cf.filename = filename
+
+	// Read from disk
+	js, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Unmarshal
+	err = json.Unmarshal(js, &cf)
+	if err != nil {
+		toggledlog.Warn.Printf("Failed to unmarshal config file")
+		return nil, nil, err
+	}
+
+	if cf.Version != contentenc.CurrentVersion {
+		return nil, nil, fmt.Errorf("Unsupported on-disk format %d", cf.Version)
+	}
+
+	for _, flag := range cf.FeatureFlags {
+		if cf.isFeatureFlagKnown(flag) == false {
+			return nil, nil, fmt.Errorf("Unsupported feature flag %s", flag)
+		}
+	}
+
+	// Generate derived key from password
+	scryptHash := cf.ScryptObject.DeriveKey(password)
+
+	// Unlock master key using password-based key
+	// We use stock go GCM instead of OpenSSL here as speed is not important
+	// and we get better error messages
+	cc := cryptocore.New(scryptHash, false, false)
+	ce := contentenc.New(cc, 4096)
+
+	key, err := ce.DecryptBlock(cf.EncryptedKey, 0, nil)
+	if err != nil {
+		toggledlog.Warn.Printf("failed to unlock master key: %s", err.Error())
+		toggledlog.Warn.Printf("Password incorrect.")
+		return nil, nil, err
+	}
+
+	return key, &cf, nil
+}
+
+// EncryptKey - encrypt "key" using an scrypt hash generated from "password"
+// and store it in cf.EncryptedKey.
+// Uses scrypt with cost parameter logN and stores the scrypt parameters in
+// cf.ScryptObject.
+func (cf *ConfFile) EncryptKey(key []byte, password string, logN int) {
+	// Generate derived key from password
+	cf.ScryptObject = NewScryptKdf(logN)
+	scryptHash := cf.ScryptObject.DeriveKey(password)
+
+	// Lock master key using password-based key
+	cc := cryptocore.New(scryptHash, false, false)
+	ce := contentenc.New(cc, 4096)
+	cf.EncryptedKey = ce.EncryptBlock(key, 0, nil)
+}
+
+// WriteFile - write out config in JSON format to file "filename.tmp"
+// then rename over "filename".
+// This way a password change atomically replaces the file.
+func (cf *ConfFile) WriteFile() error {
+	tmp := cf.filename + ".tmp"
+	// 0400 permissions: gocryptfs.conf should be kept secret and never be written to.
+	fd, err := os.OpenFile(tmp, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0400)
+	if err != nil {
+		return err
+	}
+	js, err := json.MarshalIndent(cf, "", "\t")
+	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
+}
+
+const (
+	// Understood Feature Flags.
+	// Also teach isFeatureFlagKnown() about any additions and
+	// add it to CreateConfFile() if you want to have it enabled by default.
+	FlagPlaintextNames = "PlaintextNames"
+	FlagDirIV          = "DirIV"
+	FlagEMENames       = "EMENames"
+	FlagGCMIV128       = "GCMIV128"
+)
+
+// Verify that we understand a feature flag
+func (cf *ConfFile) isFeatureFlagKnown(flag string) bool {
+	switch flag {
+	case FlagPlaintextNames, FlagDirIV, FlagEMENames, FlagGCMIV128:
+		return true
+	default:
+		return false
+	}
+}
+
+// isFeatureFlagSet - is the feature flag "flagWant" enabled?
+func (cf *ConfFile) IsFeatureFlagSet(flagWant string) bool {
+	if !cf.isFeatureFlagKnown(flagWant) {
+		log.Panicf("BUG: Tried to use unsupported feature flag %s", flagWant)
+	}
+	for _, flag := range cf.FeatureFlags {
+		if flag == flagWant {
+			return true
+		}
+	}
+	return false
+}