upstream: support for user-verified FIDO keys

FIDO2 supports a notion of "user verification" where the user is
required to demonstrate their identity to the token before particular
operations (e.g. signing). Typically this is done by authenticating
themselves using a PIN that has been set on the token.

This adds support for generating and using user verified keys where
the verification happens via PIN (other options might be added in the
future, but none are in common use now). Practically, this adds
another key generation option "verify-required" that yields a key that
requires a PIN before each authentication.

feedback markus@ and Pedro Martelletto; ok markus@

OpenBSD-Commit-ID: 57fd461e4366f87c47502c5614ec08573e6d6a15

1 files changed, 26 insertions, 12 deletions

diff --git a/sk-usbhid.c b/sk-usbhid.c
index 2a573caa2..1dd834883 100644
--- a/sk-usbhid.c
+++ b/sk-usbhid.c
@@ -163,7 +163,8 @@ pick_first_device(void)
 /* Check if the specified key handle exists on a given device. */
 static int
 try_device(fido_dev_t *dev, const uint8_t *message, size_t message_len,
-    const char *application, const uint8_t *key_handle, size_t key_handle_len)
+    const char *application, const uint8_t *key_handle, size_t key_handle_len,
+    uint8_t flags, const char *pin)
 {
         fido_assert_t *assert = NULL;
         int r = FIDO_ERR_INTERNAL;
@@ -191,7 +192,7 @@ try_device(fido_dev_t *dev, const uint8_t *message, size_t message_len,
                 skdebug(__func__, "fido_assert_up: %s", fido_strerr(r));
                 goto out;
         }
-        r = fido_dev_get_assert(dev, assert, NULL);
+        r = fido_dev_get_assert(dev, assert, pin);
         skdebug(__func__, "fido_dev_get_assert: %s", fido_strerr(r));
         if (r == FIDO_ERR_USER_PRESENCE_REQUIRED) {
                 /* U2F tokens may return this */
@@ -206,7 +207,8 @@ try_device(fido_dev_t *dev, const uint8_t *message, size_t message_len,
 /* Iterate over configured devices looking for a specific key handle */
 static fido_dev_t *
 find_device(const char *path, const uint8_t *message, size_t message_len,
-    const char *application, const uint8_t *key_handle, size_t key_handle_len)
+    const char *application, const uint8_t *key_handle, size_t key_handle_len,
+    uint8_t flags, const char *pin)
 {
         fido_dev_info_t *devlist = NULL;
         fido_dev_t *dev = NULL;
@@ -260,7 +262,7 @@ find_device(const char *path, const uint8_t *message, size_t message_len,
                         continue;
                 }
                 if (try_device(dev, message, message_len, application,
-                    key_handle, key_handle_len) == 0) {
+                    key_handle, key_handle_len, flags, pin) == 0) {
                         skdebug(__func__, "found key");
                         break;
                 }
@@ -570,19 +572,23 @@ sk_enroll(uint32_t alg, const uint8_t *challenge, size_t challenge_len,
                 skdebug(__func__, "fido_dev_open: %s", fido_strerr(r));
                 goto out;
         }
-        if ((flags & SSH_SK_RESIDENT_KEY) != 0) {
+        if ((flags & (SSH_SK_RESIDENT_KEY|SSH_SK_USER_VERIFICATION_REQD)) != 0) {
                 if (check_sk_extensions(dev, "credProtect", &credprot) < 0) {
                         skdebug(__func__, "check_sk_extensions failed");
                         goto out;
                 }
                 if (credprot == 0) {
                         skdebug(__func__, "refusing to create unprotected "
-                            "resident key");
+                            "resident/verify-required key");
                         ret = SSH_SK_ERR_UNSUPPORTED;
                         goto out;
                 }
-                if ((r = fido_cred_set_prot(cred,
-                    FIDO_CRED_PROT_UV_OPTIONAL_WITH_ID)) != FIDO_OK) {
+                if ((flags & SSH_SK_USER_VERIFICATION_REQD))
+                        credprot = FIDO_CRED_PROT_UV_REQUIRED;
+                else
+                        credprot = FIDO_CRED_PROT_UV_OPTIONAL_WITH_ID;
+
+                if ((r = fido_cred_set_prot(cred, credprot)) != FIDO_OK) {
                         skdebug(__func__, "fido_cred_set_prot: %s",
                             fido_strerr(r));
                         ret = fidoerr_to_skerr(r);
@@ -826,7 +832,7 @@ sk_sign(uint32_t alg, const uint8_t *data, size_t datalen,
                 goto out;
         }
         if ((dev = find_device(device, message, sizeof(message),
-            application, key_handle, key_handle_len)) == NULL) {
+            application, key_handle, key_handle_len, flags, pin)) == NULL) {
                 skdebug(__func__, "couldn't find device for key handle");
                 goto out;
         }
@@ -855,8 +861,15 @@ sk_sign(uint32_t alg, const uint8_t *data, size_t datalen,
                 skdebug(__func__, "fido_assert_set_up: %s", fido_strerr(r));
                 goto out;
         }
-        if ((r = fido_dev_get_assert(dev, assert, NULL)) != FIDO_OK) {
+        if (pin == NULL && (flags & SSH_SK_USER_VERIFICATION_REQD) &&
+            (r = fido_assert_set_uv(assert, FIDO_OPT_TRUE)) != FIDO_OK) {
+                skdebug(__func__, "fido_assert_set_uv: %s", fido_strerr(r));
+                ret = FIDO_ERR_PIN_REQUIRED;
+                goto out;
+        }
+        if ((r = fido_dev_get_assert(dev, assert, pin)) != FIDO_OK) {
                 skdebug(__func__, "fido_dev_get_assert: %s", fido_strerr(r));
+                ret = fidoerr_to_skerr(r);
                 goto out;
         }
         if ((response = calloc(1, sizeof(*response))) == NULL) {
@@ -978,8 +991,9 @@ read_rks(const char *devpath, const char *pin,
                                 continue;
                         }
                         skdebug(__func__, "Device %s RP \"%s\" slot %zu: "
-                            "type %d", devpath, fido_credman_rp_id(rp, i), j,
-                            fido_cred_type(cred));
+                            "type %d flags 0x%02x prot 0x%02x", devpath,
+                            fido_credman_rp_id(rp, i), j, fido_cred_type(cred),
+                            fido_cred_flags(cred), fido_cred_prot(cred));
 
                         /* build response entry */
                         if ((srk = calloc(1, sizeof(*srk))) == NULL ||