xref: /netbsd-src/usr.sbin/syslogd/sign.c (revision 4497207b84ceb51909573ae0471b6d19ed110de0)

/*	$NetBSD: sign.c,v 1.9 2022/11/08 01:03:27 uwe Exp $	*/

/*-
 * Copyright (c) 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Martin Sch�tte.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *        This product includes software developed by the NetBSD
 *        Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
/*
 * sign.c
 * syslog-sign related code for syslogd
 *
 * Martin Sch�tte
 */
/*
 * Issues with the current internet draft:
 * 1. The draft is a bit unclear on the input format for the signature,
 *    so this might have to be changed later. Cf. sign_string_sign()
 * 2. The draft only defines DSA signatures. I hope it will be extended
 *    to DSS, thus allowing DSA, RSA (ANSI X9.31) and ECDSA (ANSI X9.62)
 * 3. The draft does not define the data format for public keys in CBs.
 *    This implementation sends public keys in DER encoding.
 * 4. This current implementation uses high-level OpenSSL API.
 *    I am not sure if these completely implement the FIPS/ANSI standards.
 * Update after WG discussion in August:
 * 1. check; next draft will be clearer and specify the format as implemented.
 * 2. check; definitely only DSA in this version.
 * 3. remains a problem, so far no statement from authors or WG.
 * 4. check; used EVP_sha1 method implements FIPS.
 */
/*
 * Limitations of this implementation:
 * - cannot use OpenPGP keys, only PKIX or DSA due to OpenSSL capabilities
 * - only works for correctly formatted messages, because incorrect messages
 *   are reformatted (e.g. if it receives a message with two spaces between
 *   fields it might even be parsed, but the output will have only one space).
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: sign.c,v 1.9 2022/11/08 01:03:27 uwe Exp $");

#ifndef DISABLE_SIGN
#include "syslogd.h"
#ifndef DISABLE_TLS
#include "tls.h"
#endif /* !DISABLE_TLS */
#include "sign.h"
#include "extern.h"

/*
 * init all SGs for a given algorithm
 */
bool
sign_global_init(struct filed *Files)
{
	DPRINTF((D_CALL|D_SIGN), "sign_global_init()\n");
	if (!(GlobalSign.sg == 0 || GlobalSign.sg == 1
	   || GlobalSign.sg == 2 || GlobalSign.sg == 3)) {
		logerror("sign_init(): invalid SG %d", GlobalSign.sg);
		return false;
	}

	if (!sign_get_keys())
		return false;

	/* signature algorithm */
	/* can probably be merged with the hash algorithm/context but
	 * I leave the optimization for later until the RFC is ready */
	GlobalSign.sigctx = EVP_MD_CTX_create();
	EVP_MD_CTX_init(GlobalSign.sigctx);

	/* the signature algorithm depends on the type of key */
	switch (EVP_PKEY_base_id(GlobalSign.pubkey)) {
	case EVP_PKEY_DSA:
		GlobalSign.sig = EVP_sha1();
		GlobalSign.sig_len_b64 = SIGN_B64SIGLEN_DSS;
		break;
#ifdef notyet
	/* this is the place to add non-DSA key types and algorithms */
	case EVP_PKEY_RSA:
		GlobalSign.sig = EVP_sha1();
		GlobalSign.sig_len_b64 = 28;
		break;
#endif
	default:
		logerror("key type not supported for syslog-sign");
		return false;
	}

	assert(GlobalSign.keytype == 'C' || GlobalSign.keytype == 'K');
	assert(GlobalSign.pubkey_b64 && GlobalSign.privkey &&
	    GlobalSign.pubkey);

	GlobalSign.gbc = 0;
	STAILQ_INIT(&GlobalSign.SigGroups);

	/* hash algorithm */
	OpenSSL_add_all_digests();
	GlobalSign.mdctx = EVP_MD_CTX_create();
	EVP_MD_CTX_init(GlobalSign.mdctx);

	/* values for SHA-1 */
	GlobalSign.md = EVP_sha1();
	GlobalSign.md_len_b64 = 28;
	GlobalSign.ver = "0111";

	if (!sign_sg_init(Files))
		return false;
	sign_new_reboot_session();

	DPRINTF(D_SIGN, "length values: SIGN_MAX_SD_LENGTH %d, "
	    "SIGN_MAX_FRAG_LENGTH %d, SIGN_MAX_SB_LENGTH %d, "
	    "SIGN_MAX_HASH_NUM %d\n", SIGN_MAX_SD_LENGTH,
	    SIGN_MAX_FRAG_LENGTH, SIGN_MAX_SB_LENGTH, SIGN_MAX_HASH_NUM);

	/* set just before return, so it indicates initialization */
	GlobalSign.rsid = now;
	return true;
}

/*
 * get keys for syslog-sign
 * either from the X.509 certificate used for TLS
 * or by generating a new one
 *
 * sets the global variables
 * GlobalSign.keytype, GlobalSign.pubkey_b64,
 * GlobalSign.privkey, and GlobalSign.pubkey
 */
bool
sign_get_keys(void)
{
	EVP_PKEY *pubkey = NULL, *privkey = NULL;
	unsigned char *der_pubkey = NULL, *ptr_der_pubkey = NULL;
	char *pubkey_b64 = NULL;
	int der_len;

	/* try PKIX/TLS key first */
#ifndef DISABLE_TLS
	SSL *ssl;
	if (tls_opt.global_TLS_CTX
	 && (ssl = SSL_new(tls_opt.global_TLS_CTX))) {
		X509 *cert;
		DPRINTF(D_SIGN, "Try to get keys from TLS X.509 cert...\n");

		if (!(cert = SSL_get_certificate(ssl))) {
			logerror("SSL_get_certificate() failed");
			FREE_SSL(ssl);
			return false;
		}
		if (!(privkey = SSL_get_privatekey(ssl))) {
			logerror("SSL_get_privatekey() failed");
			FREE_SSL(ssl);
			return false;
		}
		if (!(pubkey = X509_get_pubkey(cert))) {
			logerror("X509_get_pubkey() failed");
			FREE_SSL(ssl);
			return false;
		}
		/* note:
		 * - privkey is just a pointer into SSL_CTX and
		 *   must not be changed nor be free()d
		 * - but pubkey has to be freed with EVP_PKEY_free()
		 */
		FREE_SSL(ssl);

		if (EVP_PKEY_DSA != EVP_PKEY_base_id(pubkey)) {
			DPRINTF(D_SIGN, "X.509 cert has no DSA key\n");
			EVP_PKEY_free(pubkey);
			privkey = NULL;
			pubkey = NULL;
		} else {
			DPRINTF(D_SIGN, "Got public and private key "
			    "from X.509 --> use type PKIX\n");
			GlobalSign.keytype = 'C';
			GlobalSign.privkey = privkey;
			GlobalSign.pubkey = pubkey;

			/* base64 certificate encoding */
			der_len = i2d_X509(cert, NULL);
			if (!(ptr_der_pubkey = der_pubkey = malloc(der_len))
			    || !(pubkey_b64 = malloc(der_len*2))) {
				free(der_pubkey);
				logerror("malloc() failed");
				return false;
			}
			if (i2d_X509(cert, &ptr_der_pubkey) <= 0) {
				logerror("i2d_X509() failed");
				return false;
			}
			b64_ntop(der_pubkey, der_len, pubkey_b64, der_len*2);
			free(der_pubkey);
			/* try to resize memory object as needed */
			GlobalSign.pubkey_b64 = realloc(pubkey_b64,
							strlen(pubkey_b64)+1);
			if (!GlobalSign.pubkey_b64)
				GlobalSign.pubkey_b64 = pubkey_b64;
		}
	}
#endif /* !DISABLE_TLS */
	if (!(privkey && pubkey)) { /* PKIX not available --> generate key */
		DSA *dsa;

		DPRINTF(D_SIGN, "Unable to get keys from X.509 "
			"--> use DSA with type 'K'\n");
		if (!(privkey = EVP_PKEY_new())) {
			logerror("EVP_PKEY_new() failed");
			return false;
		}
		if ((dsa = DSA_new()) == NULL) {
			logerror("DSA_new() failed");
			return false;
		}
		if (!DSA_generate_parameters_ex(dsa, SIGN_GENCERT_BITS, NULL, 0,
			NULL, NULL, NULL)) {
			logerror("DSA_generate_parameters_ex() failed");
			return false;
		}
		if (!DSA_generate_key(dsa)) {
			logerror("DSA_generate_key() failed");
			return false;
		}
		if (!EVP_PKEY_assign_DSA(privkey, dsa)) {
			logerror("EVP_PKEY_assign_DSA() failed");
			return false;
		}
		GlobalSign.keytype = 'K';  /* public/private keys used */
		GlobalSign.privkey = privkey;
		GlobalSign.pubkey = privkey;

		/* pubkey base64 encoding */
		der_len = i2d_DSA_PUBKEY(dsa, NULL);
		if (!(ptr_der_pubkey = der_pubkey = malloc(der_len))
		 || !(pubkey_b64 = malloc(der_len*2))) {
			free(der_pubkey);
			logerror("malloc() failed");
			return false;
		}
		if (i2d_DSA_PUBKEY(dsa, &ptr_der_pubkey) <= 0) {
			logerror("i2d_DSA_PUBKEY() failed");
			free(der_pubkey);
			free(pubkey_b64);
			return false;
		}
		b64_ntop(der_pubkey, der_len, pubkey_b64, der_len*2);
		free(der_pubkey);
		/* try to resize memory object as needed */
		GlobalSign.pubkey_b64 = realloc(pubkey_b64,
		    strlen(pubkey_b64) + 1);
		if (!GlobalSign.pubkey_b64)
			GlobalSign.pubkey_b64 = pubkey_b64;
	}
	return true;
}

/*
 * init SGs
 */
bool
sign_sg_init(struct filed *Files)
{
	struct signature_group_t *sg, *newsg, *last_sg;
	struct filed_queue	 *fq;
	struct string_queue	 *sqentry, *last_sqentry;
	struct filed *f;
	unsigned int i;

	/* note on SG 1 and 2:
	 * it is assumed that redundant signature groups
	 * and especially signature groups without an associated
	 * destination are harmless.
	 * this currently holds true because sign_append_hash()
	 * is called from fprintlog(), so only actually used
	 * signature group get hashes and need memory for them
	 */
	/* possible optimization for SGs 1 and 2:
	 * use a struct signature_group_t *newsg[IETF_NUM_PRIVALUES]
	 * for direct group lookup
	 */

#define ALLOC_OR_FALSE(x) do {				\
	if(!((x) = calloc(1, sizeof(*(x))))) {		\
		logerror("Unable to allocate memory");	\
		return false;				\
	}						\
} while (0)

#define ALLOC_SG(x) do {				\
	ALLOC_OR_FALSE(x);				\
	(x)->last_msg_num = 1; /* cf. section 4.2.5 */	\
	STAILQ_INIT(&(x)->hashes);			\
	STAILQ_INIT(&(x)->files);			\
} while (0)

/* alloc(fq) and add to SGs file queue */
#define ASSIGN_FQ() do {				\
	ALLOC_OR_FALSE(fq);				\
	fq->f = f;					\
	f->f_sg = newsg;				\
	DPRINTF(D_SIGN, "SG@%p <--> f@%p\n", newsg, f); \
	STAILQ_INSERT_TAIL(&newsg->files, fq, entries); \
} while (0)

	switch (GlobalSign.sg) {
	case 0:
		/* one SG, linked to all files */
		ALLOC_SG(newsg);
		newsg->spri = 0;
		for (f = Files; f; f = f->f_next)
			ASSIGN_FQ();
		STAILQ_INSERT_TAIL(&GlobalSign.SigGroups,
			newsg, entries);
		break;
	case 1:
		/* every PRI gets one SG */
		for (i = 0; i < IETF_NUM_PRIVALUES; i++) {
			int fac, prilev;
			fac = LOG_FAC(i);
			prilev = LOG_PRI(i);
			ALLOC_SG(newsg);
			newsg->spri = i;

			/* now find all destinations associated with this SG */
			for (f = Files; f; f = f->f_next)
				/* check priorities */
				if (MATCH_PRI(f, fac, prilev))
					ASSIGN_FQ();
			STAILQ_INSERT_TAIL(&GlobalSign.SigGroups,
				newsg, entries);
		}
		break;
	case 2:
		/* PRI ranges get one SG, boundaries given by the
		 * SPRI, indicating the largest PRI in the SG
		 *
		 * either GlobalSign.sig2_delims has a list of
		 * user configured delimiters, or we use a default
		 * and set up one SG per facility
		 */
		if (STAILQ_EMPTY(&GlobalSign.sig2_delims)) {
			DPRINTF(D_SIGN, "sign_sg_init(): set default "
			    "values for SG 2\n");
			for (i = 0; i < (IETF_NUM_PRIVALUES>>3); i++) {
				ALLOC_OR_FALSE(sqentry);
				sqentry->data = NULL;
				sqentry->key = (i<<3);
				STAILQ_INSERT_TAIL(&GlobalSign.sig2_delims,
					sqentry, entries);
			}
		}
		assert(!STAILQ_EMPTY(&GlobalSign.sig2_delims));

		/* add one more group at the end */
		last_sqentry = STAILQ_LAST(&GlobalSign.sig2_delims,
			string_queue, entries);
		if (last_sqentry->key < IETF_NUM_PRIVALUES) {
			ALLOC_OR_FALSE(sqentry);
			sqentry->data = NULL;
			sqentry->key = IETF_NUM_PRIVALUES-1;
			STAILQ_INSERT_TAIL(&GlobalSign.sig2_delims,
				sqentry, entries);
		}

		STAILQ_FOREACH(sqentry, &GlobalSign.sig2_delims, entries) {
			unsigned int min_pri = 0;
			ALLOC_SG(newsg);
			newsg->spri = sqentry->key;

			/* check _all_ priorities in SG */
			last_sg = STAILQ_LAST(&GlobalSign.SigGroups,
			    signature_group_t, entries);
			if (last_sg)
				min_pri = last_sg->spri + 1;

			DPRINTF(D_SIGN, "sign_sg_init(): add SG@%p: SG=\"2\","
			    " SPRI=\"%d\" -- for msgs with "
			    "%d <= pri <= %d\n",
			    newsg, newsg->spri, min_pri, newsg->spri);
			/* now find all destinations associated with this SG */
			for (f = Files; f; f = f->f_next) {
				bool match = false;
				for (i = min_pri; i <= newsg->spri; i++) {
					int fac, prilev;
					fac = LOG_FAC(i);
					prilev = LOG_PRI(i);
					if (MATCH_PRI(f, fac, prilev)) {
						match = true;
						break;
					}
				}
				if (match)
					ASSIGN_FQ();
			}
			STAILQ_INSERT_TAIL(&GlobalSign.SigGroups,
			    newsg, entries);
		}
		break;
	case 3:
		/* every file (with flag) gets one SG */
		for (f = Files; f; f = f->f_next) {
			if (!(f->f_flags & FFLAG_SIGN)) {
				f->f_sg = NULL;
				continue;
			}
			ALLOC_SG(newsg);
			newsg->spri = f->f_file; /* not needed but shows SGs */
			ASSIGN_FQ();
			STAILQ_INSERT_TAIL(&GlobalSign.SigGroups,
			    newsg, entries);
		}
		break;
	}
	DPRINTF((D_PARSE|D_SIGN), "sign_sg_init() set up these "
	    "Signature Groups:\n");
	STAILQ_FOREACH(sg, &GlobalSign.SigGroups, entries) {
		DPRINTF((D_PARSE|D_SIGN), "SG@%p with SG=\"%d\", SPRI=\"%d\","
		    " associated files:\n", sg, GlobalSign.sg, sg->spri);
		STAILQ_FOREACH(fq, &sg->files, entries) {
			DPRINTF((D_PARSE|D_SIGN), "    f@%p with type %d\n",
			    fq->f, fq->f->f_type);
		}
	}
	return true;
}

/*
 * free all SGs for a given algorithm
 */
void
sign_global_free(void)
{
	struct signature_group_t *sg, *tmp_sg;
	struct filed_queue *fq, *tmp_fq;

	DPRINTF((D_CALL|D_SIGN), "sign_global_free()\n");
	STAILQ_FOREACH_SAFE(sg, &GlobalSign.SigGroups, entries, tmp_sg) {
		if (!STAILQ_EMPTY(&sg->hashes)) {
			/* send CB and SB twice to get minimal redundancy
			 * for the last few message hashes */
			sign_send_certificate_block(sg);
			sign_send_certificate_block(sg);
			sign_send_signature_block(sg, true);
			sign_send_signature_block(sg, true);
			sign_free_hashes(sg);
		}
		fq = STAILQ_FIRST(&sg->files);
		while (fq != NULL) {
			tmp_fq = STAILQ_NEXT(fq, entries);
			free(fq);
			fq = tmp_fq;
		}
		STAILQ_REMOVE(&GlobalSign.SigGroups,
			sg, signature_group_t, entries);
		free(sg);
	}
	sign_free_string_queue(&GlobalSign.sig2_delims);

	if (GlobalSign.privkey) {
		GlobalSign.privkey = NULL;
	}
	if (GlobalSign.pubkey) {
		EVP_PKEY_free(GlobalSign.pubkey);
		GlobalSign.pubkey = NULL;
	}
	if(GlobalSign.mdctx) {
		EVP_MD_CTX_destroy(GlobalSign.mdctx);
		GlobalSign.mdctx = NULL;
	}
	if(GlobalSign.sigctx) {
		EVP_MD_CTX_destroy(GlobalSign.sigctx);
		GlobalSign.sigctx = NULL;
	}
	FREEPTR(GlobalSign.pubkey_b64);
}

/*
 * create and send certificate block
 */
bool
sign_send_certificate_block(struct signature_group_t *sg)
{
	struct filed_queue *fq;
	struct buf_msg *buffer;
	char *tstamp;
	char payload[SIGN_MAX_PAYLOAD_LENGTH];
	char sd[SIGN_MAX_SD_LENGTH];
	size_t payload_len, fragment_len;
	size_t payload_index = 0;

	/* do nothing if CBs already sent or if there was no message in SG */
	if (!sg->resendcount
	    || ((sg->resendcount == SIGN_RESENDCOUNT_CERTBLOCK)
	    && STAILQ_EMPTY(&sg->hashes)))
		return false;

	DPRINTF((D_CALL|D_SIGN), "sign_send_certificate_block(%p)\n", sg);
	tstamp = make_timestamp(NULL, true, (size_t)-1);

	payload_len = snprintf(payload, sizeof(payload), "%s %c %s", tstamp,
		GlobalSign.keytype, GlobalSign.pubkey_b64);
	if (payload_len >= sizeof(payload)) {
		DPRINTF(D_SIGN, "Buffer too small for syslog-sign setup\n");
		return false;
	}

	while (payload_index < payload_len) {
		if (payload_len - payload_index <= SIGN_MAX_FRAG_LENGTH)
			fragment_len = payload_len - payload_index;
		else
			fragment_len = SIGN_MAX_FRAG_LENGTH;

		/* format SD */
		size_t sd_len __diagused;
		sd_len = snprintf(sd, sizeof(sd), "[ssign-cert "
		    "VER=\"%s\" RSID=\"%" PRIuFAST64 "\" SG=\"%d\" "
		    "SPRI=\"%d\" TBPL=\"%zu\" INDEX=\"%zu\" "
		    "FLEN=\"%zu\" FRAG=\"%.*s\" "
		    "SIGN=\"\"]",
		    GlobalSign.ver, GlobalSign.rsid, GlobalSign.sg,
		    sg->spri, payload_len, payload_index+1,
		    fragment_len, (int)fragment_len,
		    &payload[payload_index]);
		assert(sd_len < sizeof(sd));
		assert(sd[sd_len] == '\0');
		assert(sd[sd_len-1] == ']');
		assert(sd[sd_len-2] == '"');

		if (!sign_msg_sign(&buffer, sd, sizeof(sd)))
			return 0;
		DPRINTF((D_CALL|D_SIGN), "sign_send_certificate_block(): "
		    "calling fprintlog()\n");

		STAILQ_FOREACH(fq, &sg->files, entries) {
			/* we have to preserve the f_prevcount */
			int tmpcnt;
			tmpcnt = fq->f->f_prevcount;
			fprintlog(fq->f, buffer, NULL);
			fq->f->f_prevcount = tmpcnt;
		}
		sign_inc_gbc();
		DELREF(buffer);
		payload_index += fragment_len;
	}
	sg->resendcount--;
	return true;
}

/*
 * determine the SG for a message
 * returns NULL if -sign not configured or no SG for this priority
 */
struct signature_group_t *
sign_get_sg(int pri, struct filed *f)
{
	struct signature_group_t *sg, *rc = NULL;

	if (GlobalSign.rsid && f)
		switch (GlobalSign.sg) {
		case 0:
			rc = f->f_sg;
			break;
		case 1:
		case 2:
			STAILQ_FOREACH(sg, &GlobalSign.SigGroups, entries) {
				if (sg->spri >= (unsigned int)pri) {
					rc = sg;
					break;
				}
			}
			break;
		case 3:
			if (f->f_flags & FFLAG_SIGN)
				rc = f->f_sg;
			else
				rc = NULL;
			break;
		}

	DPRINTF((D_CALL|D_SIGN), "sign_get_sg(%d, %p) --> %p\n", pri, f, rc);
	return rc;
}

/*
 * create and send signature block
 *
 * uses a sliding window for redundancy
 * if force==true then simply send all available hashes, e.g. on shutdown
 *
 * sliding window checks implicitly assume that new hashes are appended
 * to the SG between two calls. if that is not the case (e.g. with repeated
 * messages) the queue size will shrink.
 * this has no negative consequences except generating more and shorter SBs
 * than expected and confusing the operator because two consecutive SBs will
 * have same FMNn
 */
unsigned
sign_send_signature_block(struct signature_group_t *sg, bool force)
{
	char sd[SIGN_MAX_SD_LENGTH];
	size_t sd_len;
	size_t sg_num_hashes = 0;	/* hashes in SG queue */
	size_t hashes_in_sb = 0;	/* number of hashes in current SB */
	size_t hashes_sent = 0;	/* count of hashes sent */
	struct string_queue *qentry, *old_qentry;
	struct buf_msg *buffer;
	struct filed_queue *fq;
	size_t i;

	if (!sg) return 0;
	DPRINTF((D_CALL|D_SIGN), "sign_send_signature_block(%p, %d)\n",
	    sg, force);

	STAILQ_FOREACH(qentry, &sg->hashes, entries)
		sg_num_hashes++;

	/* only act if a division is full */
	if (!sg_num_hashes
	    || (!force && (sg_num_hashes % SIGN_HASH_DIVISION_NUM)))
		return 0;

	/* if no CB sent so far then do now, just before first SB */
	if (sg->resendcount == SIGN_RESENDCOUNT_CERTBLOCK)
		sign_send_certificate_block(sg);

	/* shortly after reboot we have shorter SBs */
	hashes_in_sb = MIN(sg_num_hashes, SIGN_HASH_NUM);

	DPRINTF(D_SIGN, "sign_send_signature_block(): "
	    "sg_num_hashes = %zu, hashes_in_sb = %zu, SIGN_HASH_NUM = %d\n",
	    sg_num_hashes, hashes_in_sb, SIGN_HASH_NUM);
	if (sg_num_hashes > SIGN_HASH_NUM) {
		DPRINTF(D_SIGN, "sign_send_signature_block(): sg_num_hashes"
		    " > SIGN_HASH_NUM -- This should not happen!\n");
	}

	/* now the SD */
	qentry = STAILQ_FIRST(&sg->hashes);
	sd_len = snprintf(sd, sizeof(sd), "[ssign "
	    "VER=\"%s\" RSID=\"%" PRIuFAST64 "\" SG=\"%d\" "
	    "SPRI=\"%d\" GBC=\"%" PRIuFAST64 "\" FMN=\"%" PRIuFAST64 "\" "
	    "CNT=\"%zu\" HB=\"",
	    GlobalSign.ver, GlobalSign.rsid, GlobalSign.sg,
	    sg->spri, GlobalSign.gbc, qentry->key,
	    hashes_in_sb);
	while (hashes_sent < hashes_in_sb) {
		assert(qentry);
		sd_len += snprintf(sd+sd_len, sizeof(sd)-sd_len, "%s ",
		    qentry->data);
		hashes_sent++;
		qentry = STAILQ_NEXT(qentry, entries);
	}
	/* overwrite last space and close SD */
	assert(sd_len < sizeof(sd));
	assert(sd[sd_len] == '\0');
	assert(sd[sd_len-1] == ' ');
	sd[sd_len-1] = '\0';
	sd_len = strlcat(sd, "\" SIGN=\"\"]", sizeof(sd));

	if (sign_msg_sign(&buffer, sd, sizeof(sd))) {
		DPRINTF((D_CALL|D_SIGN), "sign_send_signature_block(): calling"
		    " fprintlog(), sending %zu out of %zu hashes\n",
		    MIN(SIGN_MAX_HASH_NUM, sg_num_hashes), sg_num_hashes);

		STAILQ_FOREACH(fq, &sg->files, entries) {
			int tmpcnt;
			tmpcnt = fq->f->f_prevcount;
			fprintlog(fq->f, buffer, NULL);
			fq->f->f_prevcount = tmpcnt;
		}
		sign_inc_gbc();
		DELREF(buffer);
	}
	/* always drop the oldest division of hashes */
	if (sg_num_hashes >= SIGN_HASH_NUM) {
		qentry = STAILQ_FIRST(&sg->hashes);
		for (i = 0; i < SIGN_HASH_DIVISION_NUM; i++) {
			old_qentry = qentry;
			qentry = STAILQ_NEXT(old_qentry, entries);
			STAILQ_REMOVE(&sg->hashes, old_qentry,
			    string_queue, entries);
			FREEPTR(old_qentry->data);
			FREEPTR(old_qentry);
		}
	}
	return hashes_sent;
}

void
sign_free_hashes(struct signature_group_t *sg)
{
	DPRINTF((D_CALL|D_SIGN), "sign_free_hashes(%p)\n", sg);
	sign_free_string_queue(&sg->hashes);
}

void
sign_free_string_queue(struct string_queue_head *sqhead)
{
	struct string_queue *qentry, *tmp_qentry;

	DPRINTF((D_CALL|D_SIGN), "sign_free_string_queue(%p)\n", sqhead);
	STAILQ_FOREACH_SAFE(qentry, sqhead, entries, tmp_qentry) {
		STAILQ_REMOVE(sqhead, qentry, string_queue, entries);
		FREEPTR(qentry->data);
		free(qentry);
	}
	assert(STAILQ_EMPTY(sqhead));
}

/*
 * hash one syslog message
 */
bool
sign_msg_hash(char *line, char **hash)
{
	unsigned char md_value[EVP_MAX_MD_SIZE];
	unsigned char md_b64[EVP_MAX_MD_SIZE*2];
	/* TODO: exact expression for b64 length? */
	unsigned md_len = 0;

	DPRINTF((D_CALL|D_SIGN), "sign_msg_hash('%s')\n", line);

	SSL_CHECK_ONE(EVP_DigestInit_ex(GlobalSign.mdctx, GlobalSign.md, NULL));
	SSL_CHECK_ONE(EVP_DigestUpdate(GlobalSign.mdctx, line, strlen(line)));
	SSL_CHECK_ONE(EVP_DigestFinal_ex(GlobalSign.mdctx, md_value, &md_len));

	b64_ntop(md_value, md_len, (char *)md_b64, EVP_MAX_MD_SIZE*2);
	*hash = strdup((char *)md_b64);

	DPRINTF((D_CALL|D_SIGN), "sign_msg_hash() --> \"%s\"\n", *hash);
	return true;
}

/*
 * append hash to SG queue
 */
bool
sign_append_hash(char *hash, struct signature_group_t *sg)
{
	struct string_queue *qentry;

	/* if one SG is shared by several destinations
	 * prevent duplicate entries */
	if ((qentry = STAILQ_LAST(&sg->hashes, string_queue, entries))
	    && !strcmp(qentry->data, hash)) {
		DPRINTF((D_CALL|D_SIGN), "sign_append_hash('%s', %p): "
		    "hash already in queue\n", hash, sg);
		return false;
	}

	MALLOC(qentry, sizeof(*qentry));
	qentry->key = sign_assign_msg_num(sg);
	qentry->data = hash;
	STAILQ_INSERT_TAIL(&sg->hashes, qentry, entries);
	DPRINTF((D_CALL|D_SIGN), "sign_append_hash('%s', %p): "
	    "#%" PRIdFAST64 "\n", hash, sg, qentry->key);
	return true;
}

/*
 * sign one syslog-sign message
 *
 * requires a ssign or ssigt-cert SD element
 * ending with ' SIGN=""]' in sd
 * linesize is available memory (= sizeof(sd))
 *
 * function will calculate signature and return a new buffer
 */
bool
sign_msg_sign(struct buf_msg **bufferptr, char *sd, size_t linesize)
{
	char *signature, *line;
	size_t linelen, tlsprefixlen, endptr, newlinelen;
	struct buf_msg *buffer;

	DPRINTF((D_CALL|D_SIGN), "sign_msg_sign()\n");
	endptr = strlen(sd);

	assert(endptr < linesize);
	assert(sd[endptr] == '\0');
	assert(sd[endptr-1] == ']');
	assert(sd[endptr-2] == '"');

	/* set up buffer */
	buffer = buf_msg_new(0);
	buffer->timestamp = make_timestamp(NULL, !BSDOutputFormat, 0);
	buffer->prog = appname;
	buffer->pid = include_pid;
	buffer->recvhost = buffer->host = LocalFQDN;
	buffer->pri = 110;
	buffer->flags = IGN_CONS|SIGN_MSG;
	buffer->sd = sd;

	/* SD ready, now format and sign */
	if (!format_buffer(buffer, &line, &linelen, NULL,
		&tlsprefixlen, NULL)) {
		DPRINTF((D_CALL|D_SIGN), "sign_send_signature_block():"
		    " format_buffer() failed\n");
		buffer->sd = NULL;
		DELREF(buffer);
		return false;
	}
	if (!sign_string_sign(line+tlsprefixlen, &signature)) {
		DPRINTF((D_CALL|D_SIGN), "sign_send_signature_block():"
		    " sign_string_sign() failed\n");
		buffer->sd = NULL;
		DELREF(buffer);
		FREEPTR(line);
		return false;
	}
	FREEPTR(line);
	sd[endptr-2] = '\0';
	newlinelen = strlcat(sd, signature, linesize);
	newlinelen = strlcat(sd, "\"]", linesize);

	if (newlinelen >= linesize) {
		DPRINTF(D_SIGN, "sign_send_signature_block(): "
		    "buffer too small\n");
		buffer->sd = NULL;
		DELREF(buffer);
		return false;
	}
	assert(newlinelen < linesize);
	assert(sd[newlinelen] == '\0');
	assert(sd[newlinelen-1] == ']');
	assert(sd[newlinelen-2] == '"');

	buffer->sd = strdup(sd);
	*bufferptr = buffer;
	return true;
}

/*
 * sign one string
 */
bool
sign_string_sign(char *line, char **signature)
{
	char buf[SIGN_MAX_LENGTH+1];
	unsigned char sig_value[SIGN_B64SIGLEN_DSS];
	unsigned char sig_b64[SIGN_B64SIGLEN_DSS];
	unsigned sig_len = 0;
	char *p, *q;
	/*
	 * The signature is calculated over the completely formatted
	 * syslog-message, including all of the PRI, HEADER, and hashes
	 * in the hash block, excluding spaces between fields, and also
	 * excluding the signature field (SD Parameter Name "SIGN", "=",
	 * and corresponding value).
	 *
	 * -- I am not quite sure which spaces are to be removed.
	 * Only the ones inside the "ssign" element or those between
	 * header fields as well?
	 */
	/* removes the string ' SIGN=""' */
	for (p = line, q = buf;
	     *p && (q - buf <= SIGN_MAX_LENGTH);) {
		if (strncmp(p, " SIGN=\"\"", 8) == 0)
			p += 8;
		*q++ = *p++;
	}
	*q = '\0';

	SSL_CHECK_ONE(EVP_SignInit(GlobalSign.sigctx, GlobalSign.sig));
	SSL_CHECK_ONE(EVP_SignUpdate(GlobalSign.sigctx, buf, q-buf));
	assert(GlobalSign.privkey);
	SSL_CHECK_ONE(EVP_SignFinal(GlobalSign.sigctx, sig_value, &sig_len,
	    GlobalSign.privkey));

	b64_ntop(sig_value, sig_len, (char *)sig_b64, sizeof(sig_b64));
	*signature = strdup((char *)sig_b64);

	DPRINTF((D_CALL|D_SIGN), "sign_string_sign('%s') --> '%s'\n",
	    buf, *signature);
	return *signature != NULL;
}

void
sign_new_reboot_session(void)
{
	struct signature_group_t *sg;

	DPRINTF((D_CALL|D_SIGN), "sign_new_reboot_session()\n");

	/* global counters */
	GlobalSign.gbc = 0;
	/* might be useful for later analysis:
	 * rebooted session IDs are sequential,
	 * normal IDs are almost always not */
	GlobalSign.rsid++;

	assert(GlobalSign.sg <= 3);
	/* reset SGs */
	STAILQ_FOREACH(sg, &GlobalSign.SigGroups, entries) {
		sg->resendcount = SIGN_RESENDCOUNT_CERTBLOCK;
		sg->last_msg_num = 1;
	}
}

/* get msg_num, increment counter, check overflow */
uint_fast64_t
sign_assign_msg_num(struct signature_group_t *sg)
{
	uint_fast64_t old;

	old = sg->last_msg_num++;
	if (sg->last_msg_num > SIGN_MAX_COUNT)
		sign_new_reboot_session();
	return old;
}


/* increment gbc, check overflow */
void
sign_inc_gbc(void)
{
	if (++GlobalSign.gbc > SIGN_MAX_COUNT)
		sign_new_reboot_session();
}
#endif /* !DISABLE_SIGN */