pki: add security key file import/export functionality

Signed-off-by: Praneeth Sarode <praneethsarode@gmail.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

include/libssh/pki_priv.h

@@ -164,6 +164,11 @@ int pki_uri_import(const char *uri_name, ssh_key *key, enum ssh_key_e key_type);
 #endif /* WITH_PKCS11_URI */
 
 bool ssh_key_size_allowed_rsa(int min_size, ssh_key key);
+
+/* Security Key Helper Functions */
+int pki_buffer_pack_sk_priv_data(ssh_buffer buffer, const ssh_key key);
+int pki_buffer_unpack_sk_priv_data(ssh_buffer buffer, ssh_key key);
+
 #ifdef __cplusplus
 }
 #endif

src/pki.c

@@ -997,10 +997,15 @@ ssh_pki_export_privkey_base64_format(const ssh_key privkey,
     /*
      * For historic reasons, the Ed25519 keys are exported in OpenSSH file
      * format by default also when built with OpenSSL.
+     *
+     * The FIDO2/U2F security keys are an extension to the SSH protocol
+     * proposed by OpenSSH, and do not have any representation in PEM format.
+     * So, they are always exported in the OpenSSH file format.
      */
 #ifdef HAVE_LIBCRYPTO
     if (format == SSH_FILE_FORMAT_DEFAULT &&
-        privkey->type != SSH_KEYTYPE_ED25519) {
+        privkey->type != SSH_KEYTYPE_ED25519 &&
+        !is_sk_key_type(privkey->type)) {
         format = SSH_FILE_FORMAT_PEM;
     }
 #endif /* HAVE_LIBCRYPTO */
@@ -1224,10 +1229,16 @@ ssh_pki_export_privkey_file_format(const ssh_key privkey,
     /*
      * For historic reasons, the Ed25519 keys are exported in OpenSSH file
      * format by default also when built with OpenSSL.
+     *
+     * The FIDO2/U2F security keys are an extension to the SSH protocol
+     * proposed by OpenSSH, and do not have any representation in PEM format.
+     * So, they are always exported in the OpenSSH file format.
      */
 #ifdef HAVE_LIBCRYPTO
     if (format == SSH_FILE_FORMAT_DEFAULT &&
-        privkey->type != SSH_KEYTYPE_ED25519) {
+        privkey->type != SSH_KEYTYPE_ED25519 &&
+        !is_sk_key_type(privkey->type)) {
+
         format = SSH_FILE_FORMAT_PEM;
     }
 #endif /* HAVE_LIBCRYPTO */
@@ -1453,6 +1464,38 @@ int pki_import_privkey_buffer(enum ssh_keytypes_e type,
         }
         break;
     }
+    case SSH_KEYTYPE_SK_ECDSA: {
+        ssh_string type_str = NULL;
+        ssh_string pubkey = NULL;
+        int nid;
+
+        rc = ssh_buffer_unpack(buffer, "SS", &type_str, &pubkey);
+        if (rc != SSH_OK) {
+            goto fail;
+        }
+
+        rc = pki_buffer_unpack_sk_priv_data(buffer, key);
+        if (rc != SSH_OK) {
+            SSH_STRING_FREE(type_str);
+            SSH_STRING_FREE(pubkey);
+            goto fail;
+        }
+
+        nid = pki_key_ecdsa_nid_from_name(ssh_string_get_char(type_str));
+        SSH_STRING_FREE(type_str);
+
+        if (nid == -1) {
+            SSH_STRING_FREE(pubkey);
+            goto fail;
+        }
+
+        rc = pki_pubkey_build_ecdsa(key, nid, pubkey);
+        SSH_STRING_FREE(pubkey);
+        if (rc != SSH_OK) {
+            goto fail;
+        }
+        break;
+    }
 #endif /* HAVE_ECC */
     case SSH_KEYTYPE_ED25519: {
         ssh_string pubkey = NULL, privkey = NULL;
@@ -1478,14 +1521,38 @@ int pki_import_privkey_buffer(enum ssh_keytypes_e type,
         }
         break;
     }
+    case SSH_KEYTYPE_SK_ED25519: {
+        ssh_string pubkey = NULL;
+
+        if (ssh_fips_mode()) {
+            SSH_LOG(SSH_LOG_TRACE, "Ed25519 keys not supported in FIPS mode");
+            goto fail;
+        }
+
+        rc = ssh_buffer_unpack(buffer, "S", &pubkey);
+        if (rc != SSH_OK) {
+            goto fail;
+        }
+
+        rc = pki_buffer_unpack_sk_priv_data(buffer, key);
+        if (rc != SSH_OK) {
+            SSH_STRING_FREE(pubkey);
+            goto fail;
+        }
+
+        rc = pki_pubkey_build_ed25519(key, pubkey);
+        SSH_STRING_FREE(pubkey);
+        if (rc != SSH_OK) {
+            goto fail;
+        }
+        break;
+    }
     case SSH_KEYTYPE_RSA_CERT01:
     case SSH_KEYTYPE_ECDSA_P256_CERT01:
     case SSH_KEYTYPE_ECDSA_P384_CERT01:
     case SSH_KEYTYPE_ECDSA_P521_CERT01:
     case SSH_KEYTYPE_ED25519_CERT01:
-    case SSH_KEYTYPE_SK_ECDSA:
     case SSH_KEYTYPE_SK_ECDSA_CERT01:
-    case SSH_KEYTYPE_SK_ED25519:
     case SSH_KEYTYPE_SK_ED25519_CERT01:
     case SSH_KEYTYPE_RSA1:
     case SSH_KEYTYPE_UNKNOWN:
@@ -2232,6 +2299,64 @@ int ssh_pki_export_privkey_to_pubkey(const ssh_key privkey,
     return SSH_OK;
 }
 
+/**
+ * @internal
+ *
+ * @brief Pack security key private data into a buffer.
+ *
+ * This function packs the common security key fields (application, flags,
+ * key handle, and reserved data) into a buffer.
+ * This is used for both ECDSA and Ed25519 security keys when exporting
+ * private key data.
+ *
+ * @param[in] buffer    The buffer to pack the security key data into.
+ *
+ * @param[in] key       The security key containing the data to pack.
+ *                      Must be a security key type (SK_ECDSA or SK_ED25519).
+ *
+ * @return              SSH_OK on success, SSH_ERROR on error.
+ *
+ * @see ssh_buffer_pack()
+ */
+int pki_buffer_pack_sk_priv_data(ssh_buffer buffer, ssh_key key)
+{
+    return ssh_buffer_pack(buffer,
+                           "SbSS",
+                           key->sk_application,
+                           key->sk_flags,
+                           key->sk_key_handle,
+                           key->sk_reserved);
+}
+
+/**
+ * @internal
+ *
+ * @brief Unpack security key private data from a buffer.
+ *
+ * This function unpacks the common security key fields (application, flags,
+ * key handle, and reserved data) from a buffer.
+ * This is used for both ECDSA and Ed25519 security keys when importing
+ * private key data.
+ *
+ * @param[in] buffer    The buffer to unpack the security key data from.
+ *
+ * @param[in] key       The security key to store the unpacked data into.
+ *                      Must be a security key type (SK_ECDSA or SK_ED25519).
+ *
+ * @return              SSH_OK on success, SSH_ERROR on error.
+ *
+ * @see ssh_buffer_unpack()
+ */
+int pki_buffer_unpack_sk_priv_data(ssh_buffer buffer, ssh_key key)
+{
+    return ssh_buffer_unpack(buffer,
+                             "SbSS",
+                             &key->sk_application,
+                             &key->sk_flags,
+                             &key->sk_key_handle,
+                             &key->sk_reserved);
+}
+
 /**
  * @internal
  *

src/pki_crypto.c

@@ -1785,7 +1785,7 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
             goto fail;
         }
 
-        if (type == SSH_KEY_PRIVATE) {
+        if (type == SSH_KEY_PRIVATE && key->type == SSH_KEYTYPE_ED25519) {
             key_len = 0;
             rc = EVP_PKEY_get_raw_private_key(key->key, NULL, &key_len);
             if (rc != 1) {
@@ -1831,15 +1831,22 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
             }
             explicit_bzero(ed25519_privkey, ED25519_KEY_LEN);
             SAFE_FREE(ed25519_privkey);
-        } else {
+        } else if (type == SSH_KEY_PRIVATE &&
+                   key->type == SSH_KEYTYPE_SK_ED25519) {
+
+            rc = pki_buffer_pack_sk_priv_data(buffer, key);
+            if (rc == SSH_ERROR) {
+                goto fail;
+            }
+        } else if (type == SSH_KEY_PUBLIC &&
+                   key->type == SSH_KEYTYPE_SK_ED25519) {
             /* public key can contain certificate sk information */
-            if (key->type == SSH_KEYTYPE_SK_ED25519) {
+            rc = ssh_buffer_add_ssh_string(buffer, key->sk_application);
-                rc = ssh_buffer_add_ssh_string(buffer, key->sk_application);
+            if (rc != SSH_OK) {
-                if (rc < 0) {
+                goto fail;
-                    goto fail;
-                }
             }
         }
+
         SAFE_FREE(ed25519_pubkey);
         break;
     case SSH_KEYTYPE_ECDSA_P256:
@@ -1944,7 +1951,8 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
         ssh_string_burn(e);
         SSH_STRING_FREE(e);
         e = NULL;
-        if (type == SSH_KEY_PRIVATE) {
+
+        if (type == SSH_KEY_PRIVATE && key->type != SSH_KEYTYPE_SK_ECDSA) {
 #if OPENSSL_VERSION_NUMBER >= 0x30000000L
             OSSL_PARAM_free(params);
             rc = EVP_PKEY_todata(key->key, EVP_PKEY_KEYPAIR, &params);
@@ -1981,10 +1989,18 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
             ssh_string_burn(d);
             SSH_STRING_FREE(d);
             d = NULL;
-        } else if (key->type == SSH_KEYTYPE_SK_ECDSA) {
+        } else if (type == SSH_KEY_PRIVATE &&
+                   key->type == SSH_KEYTYPE_SK_ECDSA) {
+
+            rc = pki_buffer_pack_sk_priv_data(buffer, key);
+            if (rc == SSH_ERROR) {
+                goto fail;
+            }
+        } else if (type == SSH_KEY_PUBLIC &&
+                   key->type == SSH_KEYTYPE_SK_ECDSA) {
             /* public key can contain certificate sk information */
             rc = ssh_buffer_add_ssh_string(buffer, key->sk_application);
-            if (rc < 0) {
+            if (rc != SSH_OK) {
                 goto fail;
             }
         }

src/pki_gcrypt.c

@@ -1600,9 +1600,21 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
                 }
             }
         } else {
-            rc = pki_ed25519_private_key_to_blob(buffer, key);
+            if (key->type == SSH_KEYTYPE_SK_ED25519) {
-            if (rc == SSH_ERROR) {
+                rc = pki_ed25519_public_key_to_blob(buffer, key);
-                goto fail;
+                if (rc == SSH_ERROR) {
+                    goto fail;
+                }
+
+                rc = pki_buffer_pack_sk_priv_data(buffer, key);
+                if (rc == SSH_ERROR) {
+                    goto fail;
+                }
+            } else {
+                rc = pki_ed25519_private_key_to_blob(buffer, key);
+                if (rc == SSH_ERROR) {
+                    goto fail;
+                }
             }
         }
         break;
@@ -1640,7 +1652,7 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
         SSH_STRING_FREE(e);
         e = NULL;
 
-        if (type == SSH_KEY_PRIVATE) {
+        if (type == SSH_KEY_PRIVATE && !is_sk_key_type(key->type)) {
             d = ssh_sexp_extract_mpi(key->ecdsa,
                                      "d",
                                      GCRYMPI_FMT_STD,
@@ -1657,7 +1669,14 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
             ssh_string_burn(d);
             SSH_STRING_FREE(d);
             d = NULL;
-        } else if (key->type == SSH_KEYTYPE_SK_ECDSA) {
+        } else if (type == SSH_KEY_PRIVATE && is_sk_key_type(key->type)) {
+            /* Add security key private data for SK_ECDSA */
+            rc = pki_buffer_pack_sk_priv_data(buffer, key);
+            if (rc == SSH_ERROR) {
+                goto fail;
+            }
+        } else if (type == SSH_KEY_PUBLIC &&
+                   key->type == SSH_KEYTYPE_SK_ECDSA) {
             /* public key can contain certificate sk information */
             rc = ssh_buffer_add_ssh_string(buffer, key->sk_application);
             if (rc < 0) {

src/pki_mbedcrypto.c

@@ -1066,7 +1066,7 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
             goto out;
         }
 
-        if (type == SSH_KEY_PRIVATE) {
+        if (type == SSH_KEY_PRIVATE && key->type != SSH_KEYTYPE_SK_ECDSA) {
             d = ssh_make_bignum_string(&key->ecdsa->MBEDTLS_PRIVATE(d));
 
             if (d == NULL) {
@@ -1078,7 +1078,14 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
             if (rc < 0) {
                 goto out;
             }
-        } else if (key->type == SSH_KEYTYPE_SK_ECDSA) {
+        } else if (type == SSH_KEY_PRIVATE &&
+                   key->type == SSH_KEYTYPE_SK_ECDSA) {
+            rc = pki_buffer_pack_sk_priv_data(buffer, key);
+            if (rc != SSH_OK) {
+                goto out;
+            }
+        } else if (type == SSH_KEY_PUBLIC &&
+                   key->type == SSH_KEYTYPE_SK_ECDSA) {
             /* public key can contain certificate sk information */
             rc = ssh_buffer_add_ssh_string(buffer, key->sk_application);
             if (rc < 0) {
@@ -1101,9 +1108,21 @@ ssh_string pki_key_to_blob(const ssh_key key, enum ssh_key_e type)
                 }
             }
         } else {
-            rc = pki_ed25519_private_key_to_blob(buffer, key);
+            if (key->type == SSH_KEYTYPE_SK_ED25519) {
-            if (rc == SSH_ERROR) {
+                rc = pki_ed25519_public_key_to_blob(buffer, key);
-                goto out;
+                if (rc == SSH_ERROR) {
+                    goto out;
+                }
+
+                rc = pki_buffer_pack_sk_priv_data(buffer, key);
+                if (rc == SSH_ERROR) {
+                    goto out;
+                }
+            } else {
+                rc = pki_ed25519_private_key_to_blob(buffer, key);
+                if (rc == SSH_ERROR) {
+                    goto out;
+                }
             }
         }
         break;