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// Package cryptocore wraps OpenSSL and Go GCM crypto and provides
// a nonce generator.
package cryptocore
import (
"crypto/aes"
"crypto/cipher"
"crypto/sha512"
"log"
"runtime"
"golang.org/x/crypto/chacha20poly1305"
"github.com/rfjakob/eme"
"github.com/rfjakob/gocryptfs/v2/internal/siv_aead"
"github.com/rfjakob/gocryptfs/v2/internal/stupidgcm"
"github.com/rfjakob/gocryptfs/v2/internal/tlog"
)
const (
// KeyLen is the cipher key length in bytes. All backends use 32 bytes.
KeyLen = 32
// AuthTagLen is the length of a authentication tag in bytes.
// All backends use 16 bytes.
AuthTagLen = 16
)
// AEADTypeEnum indicates the type of AEAD backend in use.
type AEADTypeEnum struct {
Name string
NonceSize int
}
// BackendOpenSSL specifies the OpenSSL backend.
// "AES-GCM-256-OpenSSL" in gocryptfs -speed.
var BackendOpenSSL AEADTypeEnum = AEADTypeEnum{"AES-GCM-256-OpenSSL", 16}
// BackendGoGCM specifies the Go based GCM backend.
// "AES-GCM-256-Go" in gocryptfs -speed.
var BackendGoGCM AEADTypeEnum = AEADTypeEnum{"AES-GCM-256-Go", 16}
// BackendAESSIV specifies an AESSIV backend.
// "AES-SIV-512-Go" in gocryptfs -speed.
var BackendAESSIV AEADTypeEnum = AEADTypeEnum{"AES-SIV-512-Go", siv_aead.NonceSize}
// BackendXChaCha20Poly1305 specifies XChaCha20-Poly1305-Go.
// "XChaCha20-Poly1305-Go" in gocryptfs -speed.
var BackendXChaCha20Poly1305 AEADTypeEnum = AEADTypeEnum{"XChaCha20-Poly1305-Go", chacha20poly1305.NonceSizeX}
// CryptoCore is the low level crypto implementation.
type CryptoCore struct {
// EME is used for filename encryption.
EMECipher *eme.EMECipher
// GCM or AES-SIV. This is used for content encryption.
AEADCipher cipher.AEAD
// Which backend is behind AEADCipher?
AEADBackend AEADTypeEnum
// GCM needs unique IVs (nonces)
IVGenerator *nonceGenerator
// IVLen in bytes
IVLen int
}
// New returns a new CryptoCore object or panics.
//
// Even though the "GCMIV128" feature flag is now mandatory, we must still
// support 96-bit IVs here because they were used for encrypting the master
// key in gocryptfs.conf up to gocryptfs v1.2. v1.3 switched to 128 bits.
//
// Note: "key" is either the scrypt hash of the password (when decrypting
// a config file) or the masterkey (when finally mounting the filesystem).
func New(key []byte, aeadType AEADTypeEnum, IVBitLen int, useHKDF bool, forceDecode bool) *CryptoCore {
tlog.Debug.Printf("cryptocore.New: key=%d bytes, aeadType=%v, IVBitLen=%d, useHKDF=%v, forceDecode=%v",
len(key), aeadType, IVBitLen, useHKDF, forceDecode)
if len(key) != KeyLen {
log.Panicf("Unsupported key length of %d bytes", len(key))
}
if IVBitLen != 96 && IVBitLen != 128 && IVBitLen != chacha20poly1305.NonceSizeX*8 {
log.Panicf("Unsupported IV length of %d bits", IVBitLen)
}
// Initialize EME for filename encryption.
var emeCipher *eme.EMECipher
var err error
{
var emeBlockCipher cipher.Block
if useHKDF {
emeKey := hkdfDerive(key, hkdfInfoEMENames, KeyLen)
emeBlockCipher, err = aes.NewCipher(emeKey)
for i := range emeKey {
emeKey[i] = 0
}
} else {
emeBlockCipher, err = aes.NewCipher(key)
}
if err != nil {
log.Panic(err)
}
emeCipher = eme.New(emeBlockCipher)
}
// Initialize an AEAD cipher for file content encryption.
var aeadCipher cipher.AEAD
if aeadType == BackendOpenSSL || aeadType == BackendGoGCM {
var gcmKey []byte
if useHKDF {
gcmKey = hkdfDerive(key, hkdfInfoGCMContent, KeyLen)
} else {
// Filesystems created by gocryptfs v0.7 through v1.2 don't use HKDF.
// Example: tests/example_filesystems/v0.9
gcmKey = append([]byte{}, key...)
}
switch aeadType {
case BackendOpenSSL:
if IVBitLen != 128 {
log.Panicf("stupidgcm only supports 128-bit IVs, you wanted %d", IVBitLen)
}
aeadCipher = stupidgcm.New(gcmKey, forceDecode)
case BackendGoGCM:
goGcmBlockCipher, err := aes.NewCipher(gcmKey)
if err != nil {
log.Panic(err)
}
aeadCipher, err = cipher.NewGCMWithNonceSize(goGcmBlockCipher, IVBitLen/8)
if err != nil {
log.Panic(err)
}
}
for i := range gcmKey {
gcmKey[i] = 0
}
} else if aeadType == BackendAESSIV {
if IVBitLen != 128 {
// SIV supports any nonce size, but we only use 128.
log.Panicf("AES-SIV must use 128-bit IVs, you wanted %d", IVBitLen)
}
// AES-SIV uses 1/2 of the key for authentication, 1/2 for
// encryption, so we need a 64-bytes key for AES-256. Derive it from
// the 32-byte master key using HKDF, or, for older filesystems, with
// SHA256.
var key64 []byte
if useHKDF {
key64 = hkdfDerive(key, hkdfInfoSIVContent, siv_aead.KeyLen)
} else {
s := sha512.Sum512(key)
key64 = s[:]
}
aeadCipher = siv_aead.New(key64)
for i := range key64 {
key64[i] = 0
}
} else if aeadType == BackendXChaCha20Poly1305 {
// We don't support legacy modes with XChaCha20-Poly1305
if IVBitLen != chacha20poly1305.NonceSizeX*8 {
log.Panicf("XChaCha20-Poly1305 must use 192-bit IVs, you wanted %d", IVBitLen)
}
if !useHKDF {
log.Panic("XChaCha20-Poly1305 must use HKDF, but it is disabled")
}
derivedKey := hkdfDerive(key, hkdfInfoXChaChaPoly1305Content, chacha20poly1305.KeySize)
aeadCipher, err = chacha20poly1305.NewX(derivedKey)
if err != nil {
log.Panic(err)
}
} else {
log.Panicf("unknown cipher backend %q", aeadType.Name)
}
if aeadCipher.NonceSize()*8 != IVBitLen {
log.Panicf("Mismatched aeadCipher.NonceSize*8=%d and IVBitLen=%d bits",
aeadCipher.NonceSize()*8, IVBitLen)
}
return &CryptoCore{
EMECipher: emeCipher,
AEADCipher: aeadCipher,
AEADBackend: aeadType,
IVGenerator: &nonceGenerator{nonceLen: IVBitLen / 8},
IVLen: IVBitLen / 8,
}
}
type wiper interface {
Wipe()
}
// Wipe tries to wipe secret keys from memory by overwriting them with zeros
// and/or setting references to nil.
//
// This is not bulletproof due to possible GC copies, but
// still raises to bar for extracting the key.
func (c *CryptoCore) Wipe() {
be := c.AEADBackend
if be == BackendOpenSSL || be == BackendAESSIV {
tlog.Debug.Printf("CryptoCore.Wipe: Wiping AEADBackend %s key", be.Name)
// We don't use "x, ok :=" because we *want* to crash loudly if the
// type assertion fails.
w := c.AEADCipher.(wiper)
w.Wipe()
} else {
tlog.Debug.Printf("CryptoCore.Wipe: Only nil'ing stdlib refs")
}
// We have no access to the keys (or key-equivalents) stored inside the
// Go stdlib. Best we can is to nil the references and force a GC.
c.AEADCipher = nil
c.EMECipher = nil
runtime.GC()
}
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