package configfile import ( "encoding/json" "fmt" "io/ioutil" "log" "github.com/rfjakob/gocryptfs/internal/contentenc" "github.com/rfjakob/gocryptfs/internal/cryptocore" "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 }