Subject: Add functions for key manipulation
Origin: v7-6-g6090505 <https://github.com/latchset/tang/commit/v7-6-g6090505>
Upstream-Author: Sergio Correia <scorreia@redhat.com>
Date: Fri Nov 27 09:30:49 2020 -0300

    We currently rely on the tangd-update script to read the keys and
    generate signed advertisements as well as JWKs for key derivation.

    Whenever there is a change in the directory containing the actual
    keys, we run tangd-update through a systemd file watching mechanism,
    so that we can have a cache directory with updated advertisements +
    JWKs.

    As reported in #23 and #24, this mechanism can be unreliable in
    certain situations, and having up-to-date information on the keys that
    are available is critical to tang, so the idea here is to remove this
    dependency on external scripts (e.g. tangd-update) and move this
    computation to tang itself.

    In this commit we add the related functions for key manipulation so
    that in a next step we can start using it in tang.

--- /dev/null
+++ b/src/keys.c
@@ -0,0 +1,455 @@
+/* vim: set tabstop=8 shiftwidth=4 softtabstop=4 expandtab smarttab colorcolumn=80: */
+/*
+ * Copyright (c) 2020 Red Hat, Inc.
+ * Author: Sergio Correia <scorreia@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <dirent.h>
+#include <stdio.h>
+
+#include <jose/b64.h>
+#include <jose/jwk.h>
+#include <jose/jws.h>
+
+#include "keys.h"
+
+#ifndef PATH_MAX
+#define PATH_MAX 4096
+#endif
+
+static const char**
+supported_hashes(void)
+{
+    /* TODO: check if jose has a way to export the hash algorithms it
+     * supports. */
+    static const char* hashes[] = {"S1", "S224", "S256", "S384", "S512", NULL};
+    return hashes;
+}
+
+static int
+is_hash(const char* alg)
+{
+    if (!alg) {
+        return 0;
+    }
+
+    const char** algs = supported_hashes();
+    for (size_t a = 0; algs[a]; a++) {
+        if (strcmp(alg, algs[a]) == 0) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+static json_t*
+jwk_generate(const char* alg)
+{
+    json_auto_t* jalg = json_pack("{s:s}", "alg", alg);
+    if (!jalg) {
+        fprintf(stderr, "Error packing JSON with alg %s\n", alg);
+        return NULL;
+    }
+
+    if (!jose_jwk_gen(NULL, jalg)) {
+        fprintf(stderr, "Error generating JWK with alg %s\n", alg);
+        return NULL;
+    }
+
+    return json_incref(jalg);
+}
+
+static char*
+jwk_thumbprint(const json_t* jwk, const char* alg)
+{
+    size_t elen = 0;
+    size_t dlen = 0;
+
+    if (!jwk) {
+        fprintf(stderr, "Invalid JWK\n");
+        return NULL;
+    }
+
+    if (!alg || !is_hash(alg)) {
+        fprintf(stderr, "Invalid hash algorithm (%s)\n", alg);
+        return NULL;
+    }
+
+    dlen = jose_jwk_thp_buf(NULL, NULL, alg, NULL, 0);
+    if (dlen == SIZE_MAX) {
+        fprintf(stderr, "Error determining hash size for %s\n", alg);
+        return NULL;
+    }
+
+    elen = jose_b64_enc_buf(NULL, dlen, NULL, 0);
+    if (elen == SIZE_MAX) {
+        fprintf(stderr, "Error determining encoded size for %s\n", alg);
+        return NULL;
+    }
+
+    uint8_t dec[dlen];
+    char enc[elen];
+
+    if (!jose_jwk_thp_buf(NULL, jwk, alg, dec, sizeof(dec))) {
+        fprintf(stderr, "Error making thumbprint\n");
+        return NULL;
+    }
+
+    if (jose_b64_enc_buf(dec, dlen, enc, sizeof(enc)) != elen) {
+        fprintf(stderr, "Error encoding data Base64\n");
+        return NULL;
+    }
+
+    return strndup(enc, elen);
+}
+
+void
+free_tang_keys_info(struct tang_keys_info* tki)
+{
+    if (!tki) {
+        return;
+    }
+
+    json_t* to_free[] = {tki->m_keys, tki->m_rotated_keys,
+                         tki->m_payload, tki->m_sign
+    };
+    size_t len = sizeof(to_free) / sizeof(to_free[0]);
+
+    for (size_t i = 0; i < len; i++) {
+        if (to_free[i] == NULL) {
+            continue;
+        }
+        json_decref(to_free[i]);
+    }
+    free(tki);
+}
+
+void
+cleanup_tang_keys_info(struct tang_keys_info** tki)
+{
+    if (!tki || !*tki) {
+        return;
+    }
+    free_tang_keys_info(*tki);
+    *tki = NULL;
+}
+
+static struct tang_keys_info*
+new_tang_keys_info(void)
+{
+    struct tang_keys_info* tki = calloc(1, sizeof(*tki));
+    if (!tki) {
+        return NULL;
+    }
+
+    tki->m_keys = json_array();
+    tki->m_rotated_keys = json_array();
+    tki->m_payload = json_array();
+    tki->m_sign = json_array();
+
+    if (!tki->m_keys || !tki->m_rotated_keys ||
+        !tki->m_payload || !tki->m_sign) {
+        free_tang_keys_info(tki);
+        return NULL;
+    }
+    tki->m_keys_count = 0;
+    return tki;
+}
+
+static int
+jwk_valid_for(const json_t* jwk, const char* use)
+{
+    if (!jwk || !use) {
+        return 0;
+    }
+    return jose_jwk_prm(NULL, jwk, false, use);
+}
+
+static int
+jwk_valid_for_signing_and_verifying(const json_t* jwk)
+{
+    const char* uses[] = {"sign", "verify", NULL};
+    int ret = 1;
+    for (int i = 0; uses[i]; i++) {
+        if (!jwk_valid_for(jwk, uses[i])) {
+            ret = 0;
+            break;
+        }
+    }
+    return ret;
+}
+
+static int
+jwk_valid_for_signing(const json_t* jwk)
+{
+    return jwk_valid_for(jwk, "sign");
+}
+
+static int
+jwk_valid_for_deriving_keys(const json_t* jwk)
+{
+    return jwk_valid_for(jwk, "deriveKey");
+}
+
+static void
+cleanup_str(char** str)
+{
+    if (!str || !*str) {
+        return;
+    }
+    free(*str);
+    *str = NULL;
+}
+
+static json_t*
+jwk_sign(const json_t* to_sign, const json_t* sig_keys)
+{
+    if (!sig_keys || !json_is_array(sig_keys) || !json_is_array(to_sign)) {
+        return NULL;
+    }
+
+    json_auto_t* to_sign_copy = json_deep_copy(to_sign);
+    if (!jose_jwk_pub(NULL, to_sign_copy)) {
+        fprintf(stderr, "Error removing private material from data to sign\n");
+    }
+
+    json_auto_t* payload = json_pack("{s:O}", "keys", to_sign_copy);
+    json_auto_t* sig_template = json_pack("{s:{s:s}}",
+                                          "protected", "cty", "jwk-set+json");
+
+    /* Use the template with the signing keys. */
+    json_auto_t* sig_template_arr = json_array();
+    size_t arr_size = json_array_size(sig_keys);
+    for (size_t i = 0; i < arr_size; i++) {
+        if (json_array_append(sig_template_arr, sig_template) == -1) {
+            fprintf(stderr, "Unable to append sig template to array\n");
+            return NULL;
+        }
+    }
+
+    __attribute__ ((__cleanup__(cleanup_str))) char* data_to_sign = json_dumps(payload, 0);
+    json_auto_t* jws = json_pack("{s:o}", "payload",
+                                 jose_b64_enc(data_to_sign, strlen(data_to_sign)));
+
+    if (!jose_jws_sig(NULL, jws, sig_template_arr, sig_keys)) {
+        fprintf(stderr, "Error trying to jose_jws_sign\n");
+        return NULL;
+    }
+    return json_incref(jws);
+}
+
+static json_t*
+find_by_thp(struct tang_keys_info* tki, const char* target)
+{
+    if (!tki) {
+        return NULL;
+    }
+
+    json_auto_t* keys = json_deep_copy(tki->m_keys);
+    json_array_extend(keys, tki->m_rotated_keys);
+
+    size_t idx;
+    json_t* jwk;
+    const char** hashes = supported_hashes();
+    json_array_foreach(keys, idx, jwk) {
+        for (int i = 0; hashes[i]; i++) {
+            __attribute__ ((__cleanup__(cleanup_str))) char* thumbprint = jwk_thumbprint(jwk, hashes[i]);
+            if (strcmp(thumbprint, target) != 0) {
+                continue;
+            }
+
+            if (jwk_valid_for_deriving_keys(jwk)) {
+                return json_incref(jwk);
+            } else if (jwk_valid_for_signing(jwk)) {
+                json_auto_t* sign = json_deep_copy(tki->m_sign);
+                if (json_array_append(sign, jwk) == -1) {
+                    return NULL;
+                }
+                json_auto_t* jws = jwk_sign(tki->m_payload, sign);
+                if (!jws) {
+                    return NULL;
+                }
+                return json_incref(jws);
+            }
+        }
+    }
+    return NULL;
+}
+
+static int
+prepare_payload_and_sign(struct tang_keys_info* tki)
+{
+    if (!tki) {
+        return 0;
+    }
+
+    size_t idx;
+    json_t* jwk;
+    json_array_foreach(tki->m_keys, idx, jwk) {
+        if (jwk_valid_for_signing_and_verifying(jwk)) {
+            if (json_array_append(tki->m_sign, jwk) == -1) {
+                continue;
+            }
+            if (json_array_append(tki->m_payload, jwk) == -1) {
+                continue;
+            }
+        } else if (jwk_valid_for_deriving_keys(jwk)) {
+            if (json_array_append(tki->m_payload, jwk) == -1) {
+                continue;
+            }
+        }
+    }
+    if (json_array_size(tki->m_sign) == 0 || json_array_size(tki->m_payload) == 0) {
+        return 0;
+    }
+    return 1;
+}
+
+static int
+create_new_keys(const char* jwkdir)
+{
+    const char** hashes = supported_hashes();
+    const char* alg[] = {"ES512", "ECMR", NULL};
+    char path[PATH_MAX];
+    for (int i = 0; alg[i] != NULL; i++) {
+        json_auto_t* jwk = jwk_generate(alg[i]);
+        if (!jwk) {
+            return 0;
+        }
+        __attribute__ ((__cleanup__(cleanup_str))) char* thp = jwk_thumbprint(jwk, hashes[0]);
+        if (!thp) {
+            return 0;
+        }
+        if (snprintf(path, PATH_MAX, "%s/%s.jwk", jwkdir, thp) < 0) {
+            fprintf(stderr, "Unable to prepare variable with file full path (%s)\n", thp);
+            return 0;
+        }
+        path[sizeof(path) - 1] = '\0';
+        if (json_dump_file(jwk, path, 0) == -1) {
+            fprintf(stderr, "Error saving JWK to file (%s)\n", path);
+            return 0;
+        }
+    }
+    return 1;
+}
+
+static struct tang_keys_info*
+load_keys(const char* jwkdir)
+{
+    struct tang_keys_info* tki = new_tang_keys_info();
+    if (!tki) {
+        return NULL;
+    }
+
+    struct dirent* d;
+    DIR* dir = opendir(jwkdir);
+    if (!dir) {
+        free_tang_keys_info(tki);
+        return NULL;
+    }
+
+    char filepath[PATH_MAX];
+    const char* pattern = ".jwk";
+    while ((d = readdir(dir)) != NULL) {
+        if (strcmp(d->d_name, ".") == 0 || strcmp(d->d_name, "..") == 0) {
+            continue;
+        }
+
+        char* dot = strrchr(d->d_name, '.');
+        if (!dot) {
+            continue;
+        }
+
+        if (strcmp(dot, pattern) == 0) {
+            /* Found a file with .jwk extension. */
+            if (snprintf(filepath, PATH_MAX, "%s/%s", jwkdir, d->d_name) < 0) {
+                fprintf(stderr, "Unable to prepare variable with file full path (%s); skipping\n", d->d_name);
+                continue;
+            }
+            filepath[sizeof(filepath) - 1] = '\0';
+            json_auto_t* json = json_load_file(filepath, 0, NULL);
+            if (!json) {
+                fprintf(stderr, "Invalid JSON file (%s); skipping\n", filepath);
+                continue;
+            }
+
+            json_t* arr = tki->m_keys;
+            if (d->d_name[0] == '.') {
+                arr = tki->m_rotated_keys;
+            }
+            if (json_array_append(arr, json) == -1) {
+                fprintf(stderr, "Unable to append JSON (%s) to array; skipping\n", d->d_name);
+                continue;
+            }
+            tki->m_keys_count++;
+        }
+    }
+    closedir(dir);
+    return tki;
+}
+
+struct tang_keys_info*
+read_keys(const char* jwkdir)
+{
+    struct tang_keys_info* tki = load_keys(jwkdir);
+    if (!tki) {
+        return NULL;
+    }
+
+    if (tki->m_keys_count == 0) {
+        /* Let's attempt to create a new pair of keys. */
+        free_tang_keys_info(tki);
+        if (!create_new_keys(jwkdir)) {
+            return NULL;
+        }
+        tki = load_keys(jwkdir);
+    }
+
+    if (!prepare_payload_and_sign(tki)) {
+        free_tang_keys_info(tki);
+        return NULL;
+    }
+    return tki;
+}
+
+json_t*
+find_jws(struct tang_keys_info* tki, const char* thp)
+{
+    if (!tki) {
+        return NULL;
+    }
+
+    if (thp == NULL) {
+        /* Default advertisement. */
+        json_auto_t* jws = jwk_sign(tki->m_payload, tki->m_sign);
+        if (!jws) {
+            return NULL;
+        }
+        return json_incref(jws);
+    }
+    return find_by_thp(tki, thp);
+}
+
+json_t*
+find_jwk(struct tang_keys_info* tki, const char* thp)
+{
+    if (!tki || !thp) {
+        return NULL;
+    }
+    return find_by_thp(tki, thp);
+}
--- /dev/null
+++ b/src/keys.h
@@ -0,0 +1,45 @@
+/* vim: set tabstop=8 shiftwidth=4 softtabstop=4 expandtab smarttab colorcolumn=80: */
+/*
+ * Copyright (c) 2020 Red Hat, Inc.
+ * Author: Sergio Correia <scorreia@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <jansson.h>
+#include <stddef.h>
+
+struct tang_keys_info {
+    /* Arrays. */
+    json_t* m_keys;               /* Regular keys. */
+    json_t* m_rotated_keys;       /* Rotated keys. */
+
+    json_t* m_payload;            /* Payload made of regular keys capable of
+                                   * either signing+verifying or deriving new
+                                   * keys. */
+
+    json_t* m_sign;               /* Set of signing keys made from regular
+                                     keys. */
+
+    size_t m_keys_count;          /* Number of keys (regular + rotated). */
+
+};
+
+void cleanup_tang_keys_info(struct tang_keys_info**);
+void free_tang_keys_info(struct tang_keys_info*);
+struct tang_keys_info* read_keys(const char* /* jwkdir */);
+json_t* find_jws(struct tang_keys_info* /* tki */, const char* /* thp */);
+json_t* find_jwk(struct tang_keys_info* /* tki */, const char* /* thp */);