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-rw-r--r--internal/fido2/fido2.go110
1 files changed, 110 insertions, 0 deletions
diff --git a/internal/fido2/fido2.go b/internal/fido2/fido2.go
new file mode 100644
index 0000000..ea8ffd8
--- /dev/null
+++ b/internal/fido2/fido2.go
@@ -0,0 +1,110 @@
+package fido2
+
+import (
+ "bytes"
+ "encoding/base64"
+ "fmt"
+ "io"
+ "os"
+ "os/exec"
+ "strings"
+
+ "github.com/rfjakob/gocryptfs/internal/cryptocore"
+ "github.com/rfjakob/gocryptfs/internal/exitcodes"
+ "github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+type fidoCommand int
+
+const (
+ cred fidoCommand = iota
+ assert fidoCommand = iota
+ assertWithPIN fidoCommand = iota
+)
+
+const relyingPartyID = "gocryptfs"
+
+func callFidoCommand(command fidoCommand, device string, stdin []string) ([]string, error) {
+ var cmd *exec.Cmd
+ switch command {
+ case cred:
+ cmd = exec.Command("fido2-cred", "-M", "-h", "-v", device)
+ case assert:
+ cmd = exec.Command("fido2-assert", "-G", "-h", device)
+ case assertWithPIN:
+ cmd = exec.Command("fido2-assert", "-G", "-h", "-v", device)
+ }
+ tlog.Debug.Printf("callFidoCommand: executing %q with args %v", cmd.Path, cmd.Args)
+ cmd.Stderr = os.Stderr
+ in, err := cmd.StdinPipe()
+ if err != nil {
+ return nil, err
+ }
+ for _, s := range stdin {
+ // This does not deadlock because the pipe buffer is big enough (64kiB on Linux)
+ io.WriteString(in, s+"\n")
+ }
+ in.Close()
+ out, err := cmd.Output()
+ if err != nil {
+ return nil, fmt.Errorf("%s failed with %v", cmd.Args[0], err)
+ }
+ return strings.Split(string(out), "\n"), nil
+}
+
+// Register registers a credential using a FIDO2 token
+func Register(device string, userName string) (credentialID []byte) {
+ tlog.Info.Printf("FIDO2 Register: interact with your device ...")
+ cdh := base64.StdEncoding.EncodeToString(cryptocore.RandBytes(32))
+ userID := base64.StdEncoding.EncodeToString(cryptocore.RandBytes(32))
+ stdin := []string{cdh, relyingPartyID, userName, userID}
+ out, err := callFidoCommand(cred, device, stdin)
+ if err != nil {
+ tlog.Fatal.Println(err)
+ os.Exit(exitcodes.FIDO2Error)
+ }
+ credentialID, err = base64.StdEncoding.DecodeString(out[4])
+ if err != nil {
+ tlog.Fatal.Println(err)
+ os.Exit(exitcodes.FIDO2Error)
+ }
+ return credentialID
+}
+
+// Secret generates a HMAC secret using a FIDO2 token
+func Secret(device string, credentialID []byte, salt []byte) (secret []byte) {
+ tlog.Info.Printf("FIDO2 Secret: interact with your device ...")
+ cdh := base64.StdEncoding.EncodeToString(cryptocore.RandBytes(32))
+ crid := base64.StdEncoding.EncodeToString(credentialID)
+ hmacsalt := base64.StdEncoding.EncodeToString(salt)
+ stdin := []string{cdh, relyingPartyID, crid, hmacsalt}
+ // try asserting without PIN first
+ out, err := callFidoCommand(assert, device, stdin)
+ if err != nil {
+ // if that fails, let's assert with PIN
+ out, err = callFidoCommand(assertWithPIN, device, stdin)
+ if err != nil {
+ tlog.Fatal.Println(err)
+ os.Exit(exitcodes.FIDO2Error)
+ }
+ }
+ secret, err = base64.StdEncoding.DecodeString(out[4])
+ if err != nil {
+ tlog.Fatal.Println(err)
+ os.Exit(exitcodes.FIDO2Error)
+ }
+
+ // sanity checks
+ secretLen := len(secret)
+ if secretLen < 32 {
+ tlog.Fatal.Printf("FIDO2 HMACSecret too short (%d)!\n", secretLen)
+ os.Exit(exitcodes.FIDO2Error)
+ }
+ zero := make([]byte, secretLen)
+ if bytes.Equal(zero, secret) {
+ tlog.Fatal.Printf("FIDO2 HMACSecret is all zero!")
+ os.Exit(exitcodes.FIDO2Error)
+ }
+
+ return secret
+}