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// Package configfile reads and writes gocryptfs.conf does the key
// wrapping.
package configfile
import (
"encoding/json"
"fmt"
"io/ioutil"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/cryptocore"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
import "os"
const (
// The dot "." is not used in base64url (RFC4648), hence
// we can never clash with an encrypted file.
ConfDefaultName = "gocryptfs.conf"
// In reverse mode, the config file gets stored next to the plain-text
// files. Make it hidden (start with dot) to not annoy the user.
ConfReverseName = ".gocryptfs.reverse.conf"
)
type ConfFile struct {
// gocryptfs version string
// This only documents the config file for humans who look at it. The actual
// technical info is contained in FeatureFlags.
Creator 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
// File the config is saved to. Not exported to JSON.
filename 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, creator string, gcmsiv bool) error {
var cf ConfFile
cf.filename = filename
cf.Creator = creator
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, knownFlags[FlagGCMIV128]) // 128-bit IVs
if plaintextNames {
cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagPlaintextNames])
} else {
cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagDirIV])
cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagEMENames])
cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagLongNames])
}
if gcmsiv {
cf.FeatureFlags = append(cf.FeatureFlags, knownFlags[FlagGCMSIV]) // GCM-SIV encryption mode
}
// 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 {
tlog.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)
}
// Check that all set feature flags are known
for _, flag := range cf.FeatureFlags {
if !cf.isFeatureFlagKnown(flag) {
return nil, nil, fmt.Errorf("Unsupported feature flag %q", flag)
}
}
// Check that all required feature flags are set
var requiredFlags []flagIota
if cf.IsFeatureFlagSet(FlagPlaintextNames) {
requiredFlags = requiredFlagsPlaintextNames
} else {
requiredFlags = requiredFlagsNormal
}
deprecatedFs := false
for _, i := range requiredFlags {
if !cf.IsFeatureFlagSet(i) {
fmt.Fprintf(os.Stderr, "Required feature flag %q is missing\n", knownFlags[i])
deprecatedFs = true
}
}
if deprecatedFs {
fmt.Fprintf(os.Stderr, "\033[33m"+`
The filesystem was created by gocryptfs v0.6 or earlier. This version of
gocryptfs can no longer mount the filesystem.
Please download gocryptfs v0.11 and upgrade your filesystem,
see https://github.com/rfjakob/gocryptfs/wiki/Upgrading for instructions.
If you have trouble upgrading, join the discussion at
https://github.com/rfjakob/gocryptfs/issues/29 .
`+"\033[0m")
return nil, nil, fmt.Errorf("Deprecated filesystem")
}
// 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 we only use 96-bit IVs,
// speed is not important and we get better error messages
cc := cryptocore.New(scryptHash, cryptocore.BackendGoGCM, 96)
ce := contentenc.New(cc, 4096)
tlog.Warn.Enabled = false // Silence DecryptBlock() error messages on incorrect password
key, err := ce.DecryptBlock(cf.EncryptedKey, 0, nil)
tlog.Warn.Enabled = true
if err != nil {
tlog.Warn.Printf("failed to unlock master key: %s", err.Error())
return nil, nil, fmt.Errorf("Password incorrect.")
}
return key, &cf, err
}
// 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, cryptocore.BackendGoGCM, 96)
ce := contentenc.New(cc, 4096)
cf.EncryptedKey = ce.EncryptBlock(key, 0, nil, contentenc.RandomNonce, 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)
return err
}
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