CZMQ Manual - CZMQ/4.0.3


zcert - Class for work with CURVE security certificates


//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
//  This class has draft methods, which may change over time. They are not
//  in stable releases, by default. Use --enable-drafts to enable.
//  Create and initialize a new certificate in memory
CZMQ_EXPORT zcert_t *
    zcert_new (void);

//  Accepts public/secret key pair from caller
CZMQ_EXPORT zcert_t *
    zcert_new_from (const byte *public_key, const byte *secret_key);

//  Load certificate from file
CZMQ_EXPORT zcert_t *
    zcert_load (const char *filename);

//  Destroy a certificate in memory
    zcert_destroy (zcert_t **self_p);

//  Return public part of key pair as 32-byte binary string
CZMQ_EXPORT const byte *
    zcert_public_key (zcert_t *self);

//  Return secret part of key pair as 32-byte binary string
CZMQ_EXPORT const byte *
    zcert_secret_key (zcert_t *self);

//  Return public part of key pair as Z85 armored string
CZMQ_EXPORT const char *
    zcert_public_txt (zcert_t *self);

//  Return secret part of key pair as Z85 armored string
CZMQ_EXPORT const char *
    zcert_secret_txt (zcert_t *self);

//  Set certificate metadata from formatted string.
    zcert_set_meta (zcert_t *self, const char *name, const char *format, ...) CHECK_PRINTF (3);

//  Get metadata value from certificate; if the metadata value doesn't
//  exist, returns NULL.
CZMQ_EXPORT const char *
    zcert_meta (zcert_t *self, const char *name);

//  Get list of metadata fields from certificate. Caller is responsible for
//  destroying list. Caller should not modify the values of list items.
CZMQ_EXPORT zlist_t *
    zcert_meta_keys (zcert_t *self);

//  Save full certificate (public + secret) to file for persistent storage
//  This creates one public file and one secret file (filename + "_secret").
    zcert_save (zcert_t *self, const char *filename);

//  Save public certificate only to file for persistent storage
    zcert_save_public (zcert_t *self, const char *filename);

//  Save secret certificate only to file for persistent storage
    zcert_save_secret (zcert_t *self, const char *filename);

//  Apply certificate to socket, i.e. use for CURVE security on socket.
//  If certificate was loaded from public file, the secret key will be
//  undefined, and this certificate will not work successfully.
    zcert_apply (zcert_t *self, void *socket);

//  Return copy of certificate; if certificate is NULL or we exhausted
//  heap memory, returns NULL.
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT zcert_t *
    zcert_dup (zcert_t *self);

//  Return true if two certificates have the same keys
    zcert_eq (zcert_t *self, zcert_t *compare);

//  Print certificate contents to stdout
    zcert_print (zcert_t *self);

//  Self test of this class
    zcert_test (bool verbose);

//  *** Draft method, for development use, may change without warning ***
//  Unset certificate metadata.
    zcert_unset_meta (zcert_t *self, const char *name);

Please add '@interface' section in './../src/zcert.c'.


The zcert class provides a way to create and work with security certificates for the ZMQ CURVE mechanism. A certificate contains a public + secret key pair, plus metadata. It can be used as a temporary object in memory, or persisted to disk. On disk, a certificate is stored as two files. One is public and contains only the public key. The second is secret and contains both keys. The two have the same filename, with the secret file adding "_secret". To exchange certificates, send the public file via some secure route. Certificates are not signed but are text files that can be verified by eye.

Certificates are stored in the ZPL (ZMQ RFC 4) format. They have two sections, "metadata" and "curve". The first contains a list of name = value pairs, one per line. Values may be enclosed in quotes. The curve section has a public-key = keyvalue and, for secret certificates, a secret-key = keyvalue line. The keyvalue is a Z85-encoded CURVE key.


From zcert_test method

// Create temporary directory for test files
# define TESTDIR ".test_zcert"
zsys_dir_create (TESTDIR);

// Create a simple certificate with metadata
zcert_t *cert = zcert_new ();
assert (cert);
zcert_set_meta (cert, "email", "ph@imatix.com");
zcert_set_meta (cert, "name", "Pieter Hintjens");
zcert_set_meta (cert, "organization", "iMatix Corporation");
zcert_set_meta (cert, "version", "%d", 1);
zcert_set_meta (cert, "delete_me", "now");
zcert_unset_meta (cert, "delete_me");
assert (streq (zcert_meta (cert, "email"), "ph@imatix.com"));
zlist_t *keys = zcert_meta_keys (cert);
assert (zlist_size (keys) == 4);
zlist_destroy (&keys);

// Check the dup and eq methods
zcert_t *shadow = zcert_dup (cert);
assert (zcert_eq (cert, shadow));
zcert_destroy (&shadow);

// Check we can save and load certificate
zcert_save (cert, TESTDIR "/mycert.txt");
assert (zsys_file_exists (TESTDIR "/mycert.txt"));
assert (zsys_file_exists (TESTDIR "/mycert.txt_secret"));

// Load certificate, will in fact load secret one
shadow = zcert_load (TESTDIR "/mycert.txt");
assert (shadow);
assert (zcert_eq (cert, shadow));
zcert_destroy (&shadow);

// Delete secret certificate, load public one
int rc = zsys_file_delete (TESTDIR "/mycert.txt_secret");
assert (rc == 0);
shadow = zcert_load (TESTDIR "/mycert.txt");

// 32-byte null key encodes as 40 '0' characters
assert (streq (zcert_secret_txt (shadow), FORTY_ZEROES));

zcert_destroy (&shadow);
zcert_destroy (&cert);

// Delete all test files
zdir_t *dir = zdir_new (TESTDIR, NULL);
assert (dir);
zdir_remove (dir, true);
zdir_destroy (&dir);

#if defined (__WINDOWS__)
zsys_shutdown(); #endif


The czmq manual was written by the authors in the AUTHORS file.


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Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for ØMQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/. LICENSE included with the czmq distribution.