main: try to wipe cryptocore's secret keys on unmount

Raise the bar for recovering keys from memory.

https://github.com/rfjakob/gocryptfs/issues/211

2 files changed, 21 insertions, 17 deletions

diff --git a/internal/stupidgcm/stupidgcm.go b/internal/stupidgcm/stupidgcm.go
index 9fa730f..77d6770 100644
--- a/internal/stupidgcm/stupidgcm.go
+++ b/internal/stupidgcm/stupidgcm.go
@@ -24,32 +24,32 @@ const (
 )
 
 // stupidGCM implements the cipher.AEAD interface
-type stupidGCM struct {
+type StupidGCM struct {
 	key         []byte
 	forceDecode bool
 }
 
 // Verify that we satisfy the cipher.AEAD interface
-var _ cipher.AEAD = &stupidGCM{}
+var _ cipher.AEAD = &StupidGCM{}
 
 // New returns a new cipher.AEAD implementation..
 func New(key []byte, forceDecode bool) cipher.AEAD {
 	if len(key) != keyLen {
 		log.Panicf("Only %d-byte keys are supported", keyLen)
 	}
-	return &stupidGCM{key: key, forceDecode: forceDecode}
+	return &StupidGCM{key: key, forceDecode: forceDecode}
 }
 
-func (g *stupidGCM) NonceSize() int {
+func (g *StupidGCM) NonceSize() int {
 	return ivLen
 }
 
-func (g *stupidGCM) Overhead() int {
+func (g *StupidGCM) Overhead() int {
 	return tagLen
 }
 
 // Seal encrypts "in" using "iv" and "authData" and append the result to "dst"
-func (g *stupidGCM) Seal(dst, iv, in, authData []byte) []byte {
+func (g *StupidGCM) Seal(dst, iv, in, authData []byte) []byte {
 	if len(iv) != ivLen {
 		log.Panicf("Only %d-byte IVs are supported", ivLen)
 	}
@@ -136,7 +136,7 @@ func (g *stupidGCM) Seal(dst, iv, in, authData []byte) []byte {
 }
 
 // Open decrypts "in" using "iv" and "authData" and append the result to "dst"
-func (g *stupidGCM) Open(dst, iv, in, authData []byte) ([]byte, error) {
+func (g *StupidGCM) Open(dst, iv, in, authData []byte) ([]byte, error) {
 	if len(iv) != ivLen {
 		log.Panicf("Only %d-byte IVs are supported", ivLen)
 	}
@@ -231,12 +231,12 @@ func (g *stupidGCM) Open(dst, iv, in, authData []byte) ([]byte, error) {
 	return append(dst, buf...), nil
 }
 
-// Wipe wipes the AES key from memory by overwriting it with zeros and
-// setting the reference to nil.
+// Wipe tries to wipe the AES key from memory by overwriting it with zeros
+// and setting the reference to nil.
 //
 // This is not bulletproof due to possible GC copies, but
 // still raises to bar for extracting the key.
-func (g *stupidGCM) Wipe() {
+func (g *StupidGCM) Wipe() {
 	for i := range g.key {
 		g.key[i] = 0
 	}
diff --git a/internal/stupidgcm/without_openssl.go b/internal/stupidgcm/without_openssl.go
index 0c1c149..deac342 100644
--- a/internal/stupidgcm/without_openssl.go
+++ b/internal/stupidgcm/without_openssl.go
@@ -9,7 +9,7 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/exitcodes"
 )
 
-type stupidGCM struct{}
+type StupidGCM struct{}
 
 const (
 	// BuiltWithoutOpenssl indicates if openssl been disabled at compile-time
@@ -21,28 +21,32 @@ func errExit() {
 	os.Exit(exitcodes.OpenSSL)
 }
 
-func New(_ []byte, _ bool) *stupidGCM {
+func New(_ []byte, _ bool) *StupidGCM {
 	errExit()
 	// Never reached
-	return &stupidGCM{}
+	return &StupidGCM{}
 }
 
-func (g *stupidGCM) NonceSize() int {
+func (g *StupidGCM) NonceSize() int {
 	errExit()
 	return -1
 }
 
-func (g *stupidGCM) Overhead() int {
+func (g *StupidGCM) Overhead() int {
 	errExit()
 	return -1
 }
 
-func (g *stupidGCM) Seal(_, _, _, _ []byte) []byte {
+func (g *StupidGCM) Seal(_, _, _, _ []byte) []byte {
 	errExit()
 	return nil
 }
 
-func (g *stupidGCM) Open(_, _, _, _ []byte) ([]byte, error) {
+func (g *StupidGCM) Open(_, _, _, _ []byte) ([]byte, error) {
 	errExit()
 	return nil, nil
 }
+
+func (g *StupidGCM) Wipe() {
+	errExit()
+}