upstream: ability to download FIDO2 resident keys from a token via

"ssh-keygen -K". This will save public/private keys into the current
directory.

This is handy if you move a token between hosts.

feedback & ok markus@

OpenBSD-Commit-ID: d57c1f9802f7850f00a117a1d36682a6c6d10da6

1 files changed, 163 insertions, 61 deletions

diff --git a/ssh-keygen.c b/ssh-keygen.c
index 3640a3c37..7731339f7 100644
--- a/ssh-keygen.c
+++ b/ssh-keygen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.380 2019/12/30 09:49:52 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.381 2020/01/02 22:40:09 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -2871,6 +2871,137 @@ do_moduli_screen(const char *out_file, char **opts, size_t nopts)
 #endif /* WITH_OPENSSL */
 }
 
+static char *
+private_key_passphrase(void)
+{
+        char *passphrase1, *passphrase2;
+
+        /* Ask for a passphrase (twice). */
+        if (identity_passphrase)
+                passphrase1 = xstrdup(identity_passphrase);
+        else if (identity_new_passphrase)
+                passphrase1 = xstrdup(identity_new_passphrase);
+        else {
+passphrase_again:
+                passphrase1 =
+                        read_passphrase("Enter passphrase (empty for no "
+                            "passphrase): ", RP_ALLOW_STDIN);
+                passphrase2 = read_passphrase("Enter same passphrase again: ",
+                    RP_ALLOW_STDIN);
+                if (strcmp(passphrase1, passphrase2) != 0) {
+                        /*
+                         * The passphrases do not match.  Clear them and
+                         * retry.
+                         */
+                        freezero(passphrase1, strlen(passphrase1));
+                        freezero(passphrase2, strlen(passphrase2));
+                        printf("Passphrases do not match.  Try again.\n");
+                        goto passphrase_again;
+                }
+                /* Clear the other copy of the passphrase. */
+                freezero(passphrase2, strlen(passphrase2));
+        }
+        return passphrase1;
+}
+
+static const char *
+skip_ssh_url_preamble(const char *s)
+{
+        if (strncmp(s, "ssh://", 6) == 0)
+                return s + 6;
+        else if (strncmp(s, "ssh:", 4) == 0)
+                return s + 4;
+        return s;
+}
+
+static int
+do_download_sk(const char *skprovider)
+{
+        struct sshkey **keys;
+        size_t nkeys, i;
+        int r, ok = -1;
+        char *fp, *pin, *pass = NULL, *path, *pubpath;
+        const char *ext;
+
+        if (skprovider == NULL)
+                fatal("Cannot download keys without provider");
+
+        pin = read_passphrase("Enter PIN for security key: ", RP_ALLOW_STDIN);
+        if ((r = sshsk_load_resident(skprovider, pin, &keys, &nkeys)) != 0) {
+                freezero(pin, strlen(pin));
+                error("Unable to load resident keys: %s", ssh_err(r));
+                return -1;
+        }
+        if (nkeys == 0)
+                logit("No keys to download");
+        freezero(pin, strlen(pin));
+
+        for (i = 0; i < nkeys; i++) {
+                if (keys[i]->type != KEY_ECDSA_SK &&
+                    keys[i]->type != KEY_ED25519_SK) {
+                        error("Unsupported key type %s (%d)",
+                            sshkey_type(keys[i]), keys[i]->type);
+                        continue;
+                }
+                if ((fp = sshkey_fingerprint(keys[i],
+                    fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
+                        fatal("%s: sshkey_fingerprint failed", __func__);
+                debug("%s: key %zu: %s %s %s (flags 0x%02x)", __func__, i,
+                    sshkey_type(keys[i]), fp, keys[i]->sk_application,
+                    keys[i]->sk_flags);
+                ext = skip_ssh_url_preamble(keys[i]->sk_application);
+                xasprintf(&path, "id_%s_rk%s%s",
+                    keys[i]->type == KEY_ECDSA_SK ? "ecdsa_sk" : "ed25519_sk",
+                    *ext == '\0' ? "" : "_", ext);
+
+                /* If the file already exists, ask the user to confirm. */
+                if (!confirm_overwrite(path)) {
+                        free(path);
+                        break;
+                }
+
+                /* Save the key with the application string as the comment */
+                if (pass == NULL)
+                        pass = private_key_passphrase();
+                if ((r = sshkey_save_private(keys[i], path, pass,
+                    keys[i]->sk_application, private_key_format,
+                    openssh_format_cipher, rounds)) != 0) {
+                        error("Saving key \"%s\" failed: %s",
+                            path, ssh_err(r));
+                        free(path);
+                        break;
+                }
+                if (!quiet) {
+                        printf("Saved %s key%s%s to %s\n",
+                            sshkey_type(keys[i]),
+                            *ext != '\0' ? " " : "",
+                            *ext != '\0' ? keys[i]->sk_application : "",
+                            path);
+                }
+
+                /* Save public key too */
+                xasprintf(&pubpath, "%s.pub", path);
+                free(path);
+                if ((r = sshkey_save_public(keys[i], pubpath,
+                    keys[i]->sk_application)) != 0) {
+                        free(pubpath);
+                        error("Saving public key \"%s\" failed: %s",
+                            pubpath, ssh_err(r));
+                        break;
+                }
+                free(pubpath);
+        }
+
+        if (i >= nkeys)
+                ok = 0; /* success */
+        if (pass != NULL)
+                freezero(pass, strlen(pass));
+        for (i = 0; i < nkeys; i++)
+                sshkey_free(keys[i]);
+        free(keys);
+        return ok ? 0 : -1;
+}
+
 static void
 usage(void)
 {
@@ -2891,6 +3022,8 @@ usage(void)
             "       ssh-keygen -D pkcs11\n");
 #endif
         fprintf(stderr,
+            "       ssh-keygen -K path [-w sk_provider]\n");
+        fprintf(stderr,
             "       ssh-keygen -F hostname [-lv] [-f known_hosts_file]\n"
             "       ssh-keygen -H [-f known_hosts_file]\n"
             "       ssh-keygen -R hostname [-f known_hosts_file]\n"
@@ -2920,24 +3053,23 @@ usage(void)
 int
 main(int argc, char **argv)
 {
-        char dotsshdir[PATH_MAX], comment[1024], *passphrase1, *passphrase2;
+        char dotsshdir[PATH_MAX], comment[1024], *passphrase;
         char *rr_hostname = NULL, *ep, *fp, *ra;
         struct sshkey *private, *public;
         struct passwd *pw;
         struct stat st;
-        int r, opt, type, fd;
+        int r, opt, type;
         int change_passphrase = 0, change_comment = 0, show_cert = 0;
         int find_host = 0, delete_host = 0, hash_hosts = 0;
         int gen_all_hostkeys = 0, gen_krl = 0, update_krl = 0, check_krl = 0;
         int prefer_agent = 0, convert_to = 0, convert_from = 0;
         int print_public = 0, print_generic = 0, cert_serial_autoinc = 0;
-        int do_gen_candidates = 0, do_screen_candidates = 0;
+        int do_gen_candidates = 0, do_screen_candidates = 0, download_sk = 0;
         unsigned long long cert_serial = 0;
         char *identity_comment = NULL, *ca_key_path = NULL, **opts = NULL;
         size_t i, nopts = 0;
         u_int32_t bits = 0;
         uint8_t sk_flags = SSH_SK_USER_PRESENCE_REQD;
-        FILE *f;
         const char *errstr;
         int log_level = SYSLOG_LEVEL_INFO;
         char *sign_op = NULL;
@@ -2965,8 +3097,8 @@ main(int argc, char **argv)
 
         sk_provider = getenv("SSH_SK_PROVIDER");
 
-        /* Remaining characters: dGjJKSTWx */
-        while ((opt = getopt(argc, argv, "ABHLQUXceghiklopquvy"
+        /* Remaining characters: dGjJSTWx */
+        while ((opt = getopt(argc, argv, "ABHKLQUXceghiklopquvy"
             "C:D:E:F:I:M:N:O:P:R:V:Y:Z:"
             "a:b:f:g:m:n:r:s:t:w:z:")) != -1) {
                 switch (opt) {
@@ -3046,6 +3178,9 @@ main(int argc, char **argv)
                 case 'g':
                         print_generic = 1;
                         break;
+                case 'K':
+                        download_sk = 1;
+                        break;
                 case 'P':
                         identity_passphrase = optarg;
                         break;
@@ -3261,6 +3396,8 @@ main(int argc, char **argv)
         }
         if (pkcs11provider != NULL)
                 do_download(pw);
+        if (download_sk)
+                return do_download_sk(sk_provider);
         if (print_fingerprint || print_bubblebabble)
                 do_fingerprint(pw);
         if (change_passphrase)
@@ -3356,7 +3493,7 @@ main(int argc, char **argv)
                         printf("You may need to touch your security key "
                             "to authorize key generation.\n");
                 }
-                passphrase1 = NULL;
+                passphrase = NULL;
                 for (i = 0 ; i < 3; i++) {
                         if (!quiet) {
                                 printf("You may need to touch your security "
@@ -3365,21 +3502,21 @@ main(int argc, char **argv)
                         fflush(stdout);
                         r = sshsk_enroll(type, sk_provider,
                             cert_key_id == NULL ? "ssh:" : cert_key_id,
-                            sk_flags, passphrase1, NULL, &private, NULL);
+                            sk_flags, passphrase, NULL, &private, NULL);
                         if (r == 0)
                                 break;
                         if (r != SSH_ERR_KEY_WRONG_PASSPHRASE)
                                 exit(1); /* error message already printed */
-                        if (passphrase1 != NULL)
-                                freezero(passphrase1, strlen(passphrase1));
-                        passphrase1 = read_passphrase("Enter PIN for security "
+                        if (passphrase != NULL)
+                                freezero(passphrase, strlen(passphrase));
+                        passphrase = read_passphrase("Enter PIN for security "
                             "key: ", RP_ALLOW_STDIN);
                 }
-                if (passphrase1 != NULL)
-                        freezero(passphrase1, strlen(passphrase1));
+                if (passphrase != NULL)
+                        freezero(passphrase, strlen(passphrase));
                 if (i > 3)
                         fatal("Too many incorrect PINs");
-                break;
+                break;
         default:
                 if ((r = sshkey_generate(type, bits, &private)) != 0)
                         fatal("sshkey_generate failed");
@@ -3409,35 +3546,9 @@ main(int argc, char **argv)
         /* If the file already exists, ask the user to confirm. */
         if (!confirm_overwrite(identity_file))
                 exit(1);
-        /* Ask for a passphrase (twice). */
-        if (identity_passphrase)
-                passphrase1 = xstrdup(identity_passphrase);
-        else if (identity_new_passphrase)
-                passphrase1 = xstrdup(identity_new_passphrase);
-        else {
-passphrase_again:
-                passphrase1 =
-                        read_passphrase("Enter passphrase (empty for no "
-                            "passphrase): ", RP_ALLOW_STDIN);
-                passphrase2 = read_passphrase("Enter same passphrase again: ",
-                    RP_ALLOW_STDIN);
-                if (strcmp(passphrase1, passphrase2) != 0) {
-                        /*
-                         * The passphrases do not match.  Clear them and
-                         * retry.
-                         */
-                        explicit_bzero(passphrase1, strlen(passphrase1));
-                        explicit_bzero(passphrase2, strlen(passphrase2));
-                        free(passphrase1);
-                        free(passphrase2);
-                        printf("Passphrases do not match.  Try again.\n");
-                        goto passphrase_again;
-                }
-                /* Clear the other copy of the passphrase. */
-                explicit_bzero(passphrase2, strlen(passphrase2));
-                free(passphrase2);
-        }
 
+        /* Determine the passphrase for the private key */
+        passphrase = private_key_passphrase();
         if (identity_comment) {
                 strlcpy(comment, identity_comment, sizeof(comment));
         } else {
@@ -3446,35 +3557,26 @@ passphrase_again:
         }
 
         /* Save the key with the given passphrase and comment. */
-        if ((r = sshkey_save_private(private, identity_file, passphrase1,
+        if ((r = sshkey_save_private(private, identity_file, passphrase,
             comment, private_key_format, openssh_format_cipher, rounds)) != 0) {
                 error("Saving key \"%s\" failed: %s",
                     identity_file, ssh_err(r));
-                explicit_bzero(passphrase1, strlen(passphrase1));
-                free(passphrase1);
+                freezero(passphrase, strlen(passphrase));
                 exit(1);
         }
-        /* Clear the passphrase. */
-        explicit_bzero(passphrase1, strlen(passphrase1));
-        free(passphrase1);
-
-        /* Clear the private key and the random number generator. */
+        freezero(passphrase, strlen(passphrase));
         sshkey_free(private);
 
-        if (!quiet)
-                printf("Your identification has been saved in %s.\n", identity_file);
+        if (!quiet) {
+                printf("Your identification has been saved in %s.\n",
+                    identity_file);
+        }
 
         strlcat(identity_file, ".pub", sizeof(identity_file));
-        if ((fd = open(identity_file, O_WRONLY|O_CREAT|O_TRUNC, 0644)) == -1)
+        if ((r = sshkey_save_public(public, identity_file, comment)) != 0) {
                 fatal("Unable to save public key to %s: %s",
                     identity_file, strerror(errno));
-        if ((f = fdopen(fd, "w")) == NULL)
-                fatal("fdopen %s failed: %s", identity_file, strerror(errno));
-        if ((r = sshkey_write(public, f)) != 0)
-                error("write key failed: %s", ssh_err(r));
-        fprintf(f, " %s\n", comment);
-        if (ferror(f) || fclose(f) != 0)
-                fatal("write public failed: %s", strerror(errno));
+        }
 
         if (!quiet) {
                 fp = sshkey_fingerprint(public, fingerprint_hash,