bind9/lib/isccc/cc.c

/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * SPDX-License-Identifier: MPL-2.0 AND ISC
 *
 * 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 https://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

/*
 * Copyright (C) 2001 Nominum, Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC AND NOMINUM DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*! \file */

#include <errno.h>
#include <inttypes.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <isc/assertions.h>
#include <isc/hmac.h>
#include <isc/result.h>
#include <isc/safe.h>

#include <isccc/alist.h>
#include <isccc/base64.h>
#include <isccc/cc.h>
#include <isccc/sexpr.h>
#include <isccc/symtab.h>
#include <isccc/symtype.h>
#include <isccc/util.h>

#define MAX_TAGS     256
#define DUP_LIFETIME 900
#ifndef ISCCC_MAXDEPTH
#define ISCCC_MAXDEPTH \
	10 /* Big enough for rndc which just sends a string each way. */
#endif

typedef isccc_sexpr_t *sexpr_ptr;

static unsigned char auth_hmd5[] = {
	0x05, 0x5f, 0x61, 0x75, 0x74, 0x68, /*%< len + _auth */
	ISCCC_CCMSGTYPE_TABLE,		    /*%< message type */
	0x00, 0x00, 0x00, 0x20,		    /*%< length == 32 */
	0x04, 0x68, 0x6d, 0x64, 0x35,	    /*%< len + hmd5 */
	ISCCC_CCMSGTYPE_BINARYDATA,	    /*%< message type */
	0x00, 0x00, 0x00, 0x16,		    /*%< length == 22 */
	/*
	 * The base64 encoding of one of our HMAC-MD5 signatures is
	 * 22 bytes.
	 */
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

#define HMD5_OFFSET 21 /*%< 21 = 6 + 1 + 4 + 5 + 1 + 4 */
#define HMD5_LENGTH 22

static unsigned char auth_hsha[] = {
	0x05, 0x5f, 0x61, 0x75, 0x74, 0x68, /*%< len + _auth */
	ISCCC_CCMSGTYPE_TABLE,		    /*%< message type */
	0x00, 0x00, 0x00, 0x63,		    /*%< length == 99 */
	0x04, 0x68, 0x73, 0x68, 0x61,	    /*%< len + hsha */
	ISCCC_CCMSGTYPE_BINARYDATA,	    /*%< message type */
	0x00, 0x00, 0x00, 0x59,		    /*%< length == 89 */
	0x00,				    /*%< algorithm */
	/*
	 * The base64 encoding of one of our HMAC-SHA* signatures is
	 * 88 bytes.
	 */
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00
};

#define HSHA_OFFSET 22 /*%< 21 = 6 + 1 + 4 + 5 + 1 + 4 + 1 */
#define HSHA_LENGTH 88

static isc_result_t
table_towire(isccc_sexpr_t *alist, isc_buffer_t **buffer);

static isc_result_t
list_towire(isccc_sexpr_t *alist, isc_buffer_t **buffer);

static isc_result_t
value_towire(isccc_sexpr_t *elt, isc_buffer_t **buffer) {
	unsigned int len;
	isccc_region_t *vr;
	isc_result_t result;

	if (isccc_sexpr_binaryp(elt)) {
		vr = isccc_sexpr_tobinary(elt);
		len = REGION_SIZE(*vr);
		result = isc_buffer_reserve(*buffer, 1 + 4);
		if (result != ISC_R_SUCCESS) {
			return ISC_R_NOSPACE;
		}
		isc_buffer_putuint8(*buffer, ISCCC_CCMSGTYPE_BINARYDATA);
		isc_buffer_putuint32(*buffer, len);

		result = isc_buffer_reserve(*buffer, len);
		if (result != ISC_R_SUCCESS) {
			return ISC_R_NOSPACE;
		}
		isc_buffer_putmem(*buffer, vr->rstart, len);
	} else if (isccc_alist_alistp(elt)) {
		unsigned int used;
		isc_buffer_t b;

		result = isc_buffer_reserve(*buffer, 1 + 4);
		if (result != ISC_R_SUCCESS) {
			return ISC_R_NOSPACE;
		}
		isc_buffer_putuint8(*buffer, ISCCC_CCMSGTYPE_TABLE);
		/*
		 * Emit a placeholder length.
		 */
		used = (*buffer)->used;
		isc_buffer_putuint32(*buffer, 0);

		/*
		 * Emit the table.
		 */
		result = table_towire(elt, buffer);
		if (result != ISC_R_SUCCESS) {
			return result;
		}

		len = (*buffer)->used - used;
		/*
		 * 'len' is 4 bytes too big, since it counts
		 * the placeholder length too.	Adjust and
		 * emit.
		 */
		INSIST(len >= 4U);
		len -= 4;

		isc_buffer_init(&b, (unsigned char *)(*buffer)->base + used, 4);
		isc_buffer_putuint32(&b, len);
	} else if (isccc_sexpr_listp(elt)) {
		unsigned int used;
		isc_buffer_t b;

		result = isc_buffer_reserve(*buffer, 1 + 4);
		if (result != ISC_R_SUCCESS) {
			return ISC_R_NOSPACE;
		}
		isc_buffer_putuint8(*buffer, ISCCC_CCMSGTYPE_LIST);
		/*
		 * Emit a placeholder length.
		 */
		used = (*buffer)->used;
		isc_buffer_putuint32(*buffer, 0);

		/*
		 * Emit the list.
		 */
		result = list_towire(elt, buffer);
		if (result != ISC_R_SUCCESS) {
			return result;
		}

		len = (*buffer)->used - used;
		/*
		 * 'len' is 4 bytes too big, since it counts
		 * the placeholder length too.	Adjust and
		 * emit.
		 */
		INSIST(len >= 4U);
		len -= 4;

		isc_buffer_init(&b, (unsigned char *)(*buffer)->base + used, 4);
		isc_buffer_putuint32(&b, len);
	}

	return ISC_R_SUCCESS;
}

static isc_result_t
table_towire(isccc_sexpr_t *alist, isc_buffer_t **buffer) {
	isccc_sexpr_t *kv, *elt, *k, *v;
	char *ks;
	isc_result_t result;
	unsigned int len;

	for (elt = isccc_alist_first(alist); elt != NULL;
	     elt = ISCCC_SEXPR_CDR(elt))
	{
		kv = ISCCC_SEXPR_CAR(elt);
		k = ISCCC_SEXPR_CAR(kv);
		ks = isccc_sexpr_tostring(k);
		v = ISCCC_SEXPR_CDR(kv);
		len = (unsigned int)strlen(ks);
		INSIST(len <= 255U);
		/*
		 * Emit the key name.
		 */
		result = isc_buffer_reserve(*buffer, 1 + len);
		if (result != ISC_R_SUCCESS) {
			return ISC_R_NOSPACE;
		}
		isc_buffer_putuint8(*buffer, (uint8_t)len);
		isc_buffer_putmem(*buffer, (const unsigned char *)ks, len);
		/*
		 * Emit the value.
		 */
		result = value_towire(v, buffer);
		if (result != ISC_R_SUCCESS) {
			return result;
		}
	}

	return ISC_R_SUCCESS;
}

static isc_result_t
list_towire(isccc_sexpr_t *list, isc_buffer_t **buffer) {
	isc_result_t result;

	while (list != NULL) {
		result = value_towire(ISCCC_SEXPR_CAR(list), buffer);
		if (result != ISC_R_SUCCESS) {
			return result;
		}
		list = ISCCC_SEXPR_CDR(list);
	}

	return ISC_R_SUCCESS;
}

static isc_result_t
sign(unsigned char *data, unsigned int length, unsigned char *out,
     uint32_t algorithm, isccc_region_t *secret) {
	const isc_md_type_t *md_type;
	isc_result_t result;
	isccc_region_t source, target;
	unsigned char digest[ISC_MAX_MD_SIZE];
	unsigned int digestlen = sizeof(digest);
	unsigned char digestb64[HSHA_LENGTH + 4];

	source.rstart = digest;

	switch (algorithm) {
	case ISCCC_ALG_HMACMD5:
		md_type = ISC_MD_MD5;
		break;
	case ISCCC_ALG_HMACSHA1:
		md_type = ISC_MD_SHA1;
		break;
	case ISCCC_ALG_HMACSHA224:
		md_type = ISC_MD_SHA224;
		break;
	case ISCCC_ALG_HMACSHA256:
		md_type = ISC_MD_SHA256;
		break;
	case ISCCC_ALG_HMACSHA384:
		md_type = ISC_MD_SHA384;
		break;
	case ISCCC_ALG_HMACSHA512:
		md_type = ISC_MD_SHA512;
		break;
	default:
		return ISC_R_NOTIMPLEMENTED;
	}

	result = isc_hmac(md_type, secret->rstart, REGION_SIZE(*secret), data,
			  length, digest, &digestlen);
	if (result != ISC_R_SUCCESS) {
		return result;
	}
	source.rend = digest + digestlen;

	memset(digestb64, 0, sizeof(digestb64));
	target.rstart = digestb64;
	target.rend = digestb64 + sizeof(digestb64);
	result = isccc_base64_encode(&source, 64, "", &target);
	if (result != ISC_R_SUCCESS) {
		return result;
	}
	if (algorithm == ISCCC_ALG_HMACMD5) {
		PUT_MEM(digestb64, HMD5_LENGTH, out);
	} else {
		PUT_MEM(digestb64, HSHA_LENGTH, out);
	}
	return ISC_R_SUCCESS;
}

isc_result_t
isccc_cc_towire(isccc_sexpr_t *alist, isc_buffer_t **buffer, uint32_t algorithm,
		isccc_region_t *secret) {
	unsigned int hmac_base, signed_base;
	isc_result_t result;

	result = isc_buffer_reserve(*buffer,
				    4 + ((algorithm == ISCCC_ALG_HMACMD5)
						 ? sizeof(auth_hmd5)
						 : sizeof(auth_hsha)));
	if (result != ISC_R_SUCCESS) {
		return ISC_R_NOSPACE;
	}

	/*
	 * Emit protocol version.
	 */
	isc_buffer_putuint32(*buffer, 1);

	if (secret != NULL) {
		/*
		 * Emit _auth section with zeroed HMAC signature.
		 * We'll replace the zeros with the real signature once
		 * we know what it is.
		 */
		if (algorithm == ISCCC_ALG_HMACMD5) {
			hmac_base = (*buffer)->used + HMD5_OFFSET;
			isc_buffer_putmem(*buffer, auth_hmd5,
					  sizeof(auth_hmd5));
		} else {
			unsigned char *hmac_alg;

			hmac_base = (*buffer)->used + HSHA_OFFSET;
			hmac_alg = (unsigned char *)isc_buffer_used(*buffer) +
				   HSHA_OFFSET - 1;
			isc_buffer_putmem(*buffer, auth_hsha,
					  sizeof(auth_hsha));
			*hmac_alg = algorithm;
		}
	} else {
		hmac_base = 0;
	}
	signed_base = (*buffer)->used;
	/*
	 * Delete any existing _auth section so that we don't try
	 * to encode it.
	 */
	isccc_alist_delete(alist, "_auth");
	/*
	 * Emit the message.
	 */
	result = table_towire(alist, buffer);
	if (result != ISC_R_SUCCESS) {
		return result;
	}
	if (secret != NULL) {
		return sign((unsigned char *)(*buffer)->base + signed_base,
			    (*buffer)->used - signed_base,
			    (unsigned char *)(*buffer)->base + hmac_base,
			    algorithm, secret);
	}
	return ISC_R_SUCCESS;
}

static isc_result_t
verify(isccc_sexpr_t *alist, unsigned char *data, unsigned int length,
       uint32_t algorithm, isccc_region_t *secret) {
	const isc_md_type_t *md_type;
	isccc_region_t source;
	isccc_region_t target;
	isc_result_t result;
	isccc_sexpr_t *_auth, *hmacvalue;
	unsigned char digest[ISC_MAX_MD_SIZE];
	unsigned int digestlen = sizeof(digest);
	unsigned char digestb64[HSHA_LENGTH * 4];

	/*
	 * Extract digest.
	 */
	_auth = isccc_alist_lookup(alist, "_auth");
	if (!isccc_alist_alistp(_auth)) {
		return ISC_R_FAILURE;
	}
	if (algorithm == ISCCC_ALG_HMACMD5) {
		hmacvalue = isccc_alist_lookup(_auth, "hmd5");
	} else {
		hmacvalue = isccc_alist_lookup(_auth, "hsha");
	}
	if (!isccc_sexpr_binaryp(hmacvalue)) {
		return ISC_R_FAILURE;
	}
	/*
	 * Compute digest.
	 */
	source.rstart = digest;

	switch (algorithm) {
	case ISCCC_ALG_HMACMD5:
		md_type = ISC_MD_MD5;
		break;
	case ISCCC_ALG_HMACSHA1:
		md_type = ISC_MD_SHA1;
		break;
	case ISCCC_ALG_HMACSHA224:
		md_type = ISC_MD_SHA224;
		break;
	case ISCCC_ALG_HMACSHA256:
		md_type = ISC_MD_SHA256;
		break;
	case ISCCC_ALG_HMACSHA384:
		md_type = ISC_MD_SHA384;
		break;
	case ISCCC_ALG_HMACSHA512:
		md_type = ISC_MD_SHA512;
		break;
	default:
		return ISC_R_NOTIMPLEMENTED;
	}

	result = isc_hmac(md_type, secret->rstart, REGION_SIZE(*secret), data,
			  length, digest, &digestlen);
	if (result != ISC_R_SUCCESS) {
		return result;
	}
	source.rend = digest + digestlen;

	target.rstart = digestb64;
	target.rend = digestb64 + sizeof(digestb64);
	memset(digestb64, 0, sizeof(digestb64));
	result = isccc_base64_encode(&source, 64, "", &target);
	if (result != ISC_R_SUCCESS) {
		return result;
	}

	/*
	 * Verify.
	 */
	if (algorithm == ISCCC_ALG_HMACMD5) {
		isccc_region_t *region;
		unsigned char *value;

		region = isccc_sexpr_tobinary(hmacvalue);
		if ((region->rend - region->rstart) != HMD5_LENGTH) {
			return ISCCC_R_BADAUTH;
		}
		value = region->rstart;
		if (!isc_safe_memequal(value, digestb64, HMD5_LENGTH)) {
			return ISCCC_R_BADAUTH;
		}
	} else {
		isccc_region_t *region;
		unsigned char *value;
		uint32_t valalg;

		region = isccc_sexpr_tobinary(hmacvalue);

		/*
		 * Note: with non-MD5 algorithms, there's an extra octet
		 * to identify which algorithm is in use.
		 */
		if ((region->rend - region->rstart) != HSHA_LENGTH + 1) {
			return ISCCC_R_BADAUTH;
		}
		value = region->rstart;
		GET8(valalg, value);
		if ((valalg != algorithm) ||
		    !isc_safe_memequal(value, digestb64, HSHA_LENGTH))
		{
			return ISCCC_R_BADAUTH;
		}
	}

	return ISC_R_SUCCESS;
}

static isc_result_t
table_fromwire(isccc_region_t *source, isccc_region_t *secret,
	       uint32_t algorithm, unsigned int depth, isccc_sexpr_t **alistp);

static isc_result_t
list_fromwire(isccc_region_t *source, unsigned int depth,
	      isccc_sexpr_t **listp);

static isc_result_t
value_fromwire(isccc_region_t *source, unsigned int depth,
	       isccc_sexpr_t **valuep) {
	unsigned int msgtype;
	uint32_t len;
	isccc_sexpr_t *value;
	isccc_region_t active;
	isc_result_t result;

	if (depth > ISCCC_MAXDEPTH) {
		return ISCCC_R_MAXDEPTH;
	}

	if (REGION_SIZE(*source) < 1 + 4) {
		return ISC_R_UNEXPECTEDEND;
	}
	GET8(msgtype, source->rstart);
	GET32(len, source->rstart);
	if (REGION_SIZE(*source) < len) {
		return ISC_R_UNEXPECTEDEND;
	}
	active.rstart = source->rstart;
	active.rend = active.rstart + len;
	source->rstart = active.rend;
	if (msgtype == ISCCC_CCMSGTYPE_BINARYDATA) {
		value = isccc_sexpr_frombinary(&active);
		if (value != NULL) {
			*valuep = value;
			result = ISC_R_SUCCESS;
		} else {
			result = ISC_R_NOMEMORY;
		}
	} else if (msgtype == ISCCC_CCMSGTYPE_TABLE) {
		result = table_fromwire(&active, NULL, 0, depth + 1, valuep);
	} else if (msgtype == ISCCC_CCMSGTYPE_LIST) {
		result = list_fromwire(&active, depth + 1, valuep);
	} else {
		result = DNS_R_SYNTAX;
	}

	return result;
}

static isc_result_t
table_fromwire(isccc_region_t *source, isccc_region_t *secret,
	       uint32_t algorithm, unsigned int depth, isccc_sexpr_t **alistp) {
	char key[256];
	uint32_t len;
	isc_result_t result;
	isccc_sexpr_t *alist, *value;
	bool first_tag;
	unsigned char *checksum_rstart;

	REQUIRE(alistp != NULL && *alistp == NULL);

	if (depth > ISCCC_MAXDEPTH) {
		return ISCCC_R_MAXDEPTH;
	}

	checksum_rstart = NULL;
	first_tag = true;
	alist = isccc_alist_create();
	if (alist == NULL) {
		return ISC_R_NOMEMORY;
	}

	while (!REGION_EMPTY(*source)) {
		GET8(len, source->rstart);
		if (REGION_SIZE(*source) < len) {
			result = ISC_R_UNEXPECTEDEND;
			goto bad;
		}
		GET_MEM(key, len, source->rstart);
		key[len] = '\0'; /* Ensure NUL termination. */
		value = NULL;
		result = value_fromwire(source, depth + 1, &value);
		if (result != ISC_R_SUCCESS) {
			goto bad;
		}
		if (isccc_alist_define(alist, key, value) == NULL) {
			result = ISC_R_NOMEMORY;
			goto bad;
		}
		if (first_tag && secret != NULL && strcmp(key, "_auth") == 0) {
			checksum_rstart = source->rstart;
		}
		first_tag = false;
	}

	if (secret != NULL) {
		if (checksum_rstart != NULL) {
			result = verify(
				alist, checksum_rstart,
				(unsigned int)(source->rend - checksum_rstart),
				algorithm, secret);
		} else {
			result = ISCCC_R_BADAUTH;
		}
	} else {
		result = ISC_R_SUCCESS;
	}

bad:
	if (result == ISC_R_SUCCESS) {
		*alistp = alist;
	} else {
		isccc_sexpr_free(&alist);
	}

	return result;
}

static isc_result_t
list_fromwire(isccc_region_t *source, unsigned int depth,
	      isccc_sexpr_t **listp) {
	isccc_sexpr_t *list, *value;
	isc_result_t result;

	if (depth > ISCCC_MAXDEPTH) {
		return ISCCC_R_MAXDEPTH;
	}

	list = NULL;
	while (!REGION_EMPTY(*source)) {
		value = NULL;
		result = value_fromwire(source, depth + 1, &value);
		if (result != ISC_R_SUCCESS) {
			isccc_sexpr_free(&list);
			return result;
		}
		if (isccc_sexpr_addtolist(&list, value) == NULL) {
			isccc_sexpr_free(&value);
			isccc_sexpr_free(&list);
			return ISC_R_NOMEMORY;
		}
	}

	*listp = list;

	return ISC_R_SUCCESS;
}

isc_result_t
isccc_cc_fromwire(isccc_region_t *source, isccc_sexpr_t **alistp,
		  uint32_t algorithm, isccc_region_t *secret) {
	unsigned int size;
	uint32_t version;

	size = REGION_SIZE(*source);
	if (size < 4) {
		return ISC_R_UNEXPECTEDEND;
	}
	GET32(version, source->rstart);
	if (version != 1) {
		return ISCCC_R_UNKNOWNVERSION;
	}

	return table_fromwire(source, secret, algorithm, 0, alistp);
}

static isc_result_t
createmessage(uint32_t version, const char *from, const char *to,
	      uint32_t serial, isccc_time_t now, isccc_time_t expires,
	      isccc_sexpr_t **alistp, bool want_expires) {
	isccc_sexpr_t *alist, *_ctrl, *_data;
	isc_result_t result;

	REQUIRE(alistp != NULL && *alistp == NULL);

	if (version != 1) {
		return ISCCC_R_UNKNOWNVERSION;
	}

	alist = isccc_alist_create();
	if (alist == NULL) {
		return ISC_R_NOMEMORY;
	}

	result = ISC_R_NOMEMORY;

	_ctrl = isccc_alist_create();
	if (_ctrl == NULL) {
		goto bad;
	}
	if (isccc_alist_define(alist, "_ctrl", _ctrl) == NULL) {
		isccc_sexpr_free(&_ctrl);
		goto bad;
	}

	_data = isccc_alist_create();
	if (_data == NULL) {
		goto bad;
	}
	if (isccc_alist_define(alist, "_data", _data) == NULL) {
		isccc_sexpr_free(&_data);
		goto bad;
	}

	if (isccc_cc_defineuint32(_ctrl, "_ser", serial) == NULL ||
	    isccc_cc_defineuint32(_ctrl, "_tim", now) == NULL ||
	    (want_expires &&
	     isccc_cc_defineuint32(_ctrl, "_exp", expires) == NULL))
	{
		goto bad;
	}
	if (from != NULL && isccc_cc_definestring(_ctrl, "_frm", from) == NULL)
	{
		goto bad;
	}
	if (to != NULL && isccc_cc_definestring(_ctrl, "_to", to) == NULL) {
		goto bad;
	}

	*alistp = alist;

	return ISC_R_SUCCESS;

bad:
	isccc_sexpr_free(&alist);

	return result;
}

isc_result_t
isccc_cc_createmessage(uint32_t version, const char *from, const char *to,
		       uint32_t serial, isccc_time_t now, isccc_time_t expires,
		       isccc_sexpr_t **alistp) {
	return createmessage(version, from, to, serial, now, expires, alistp,
			     true);
}

isc_result_t
isccc_cc_createack(isccc_sexpr_t *message, bool ok, isccc_sexpr_t **ackp) {
	char *_frm, *_to;
	uint32_t serial;
	isccc_sexpr_t *ack, *_ctrl;
	isc_result_t result;
	isccc_time_t t;

	REQUIRE(ackp != NULL && *ackp == NULL);

	_ctrl = isccc_alist_lookup(message, "_ctrl");
	if (!isccc_alist_alistp(_ctrl) ||
	    isccc_cc_lookupuint32(_ctrl, "_ser", &serial) != ISC_R_SUCCESS ||
	    isccc_cc_lookupuint32(_ctrl, "_tim", &t) != ISC_R_SUCCESS)
	{
		return ISC_R_FAILURE;
	}
	/*
	 * _frm and _to are optional.
	 */
	_frm = NULL;
	(void)isccc_cc_lookupstring(_ctrl, "_frm", &_frm);
	_to = NULL;
	(void)isccc_cc_lookupstring(_ctrl, "_to", &_to);
	/*
	 * Create the ack.
	 */
	ack = NULL;
	result = createmessage(1, _to, _frm, serial, t, 0, &ack, false);
	if (result != ISC_R_SUCCESS) {
		return result;
	}

	_ctrl = isccc_alist_lookup(ack, "_ctrl");
	if (_ctrl == NULL) {
		result = ISC_R_FAILURE;
		goto bad;
	}
	if (isccc_cc_definestring(ack, "_ack", (ok) ? "1" : "0") == NULL) {
		result = ISC_R_NOMEMORY;
		goto bad;
	}

	*ackp = ack;

	return ISC_R_SUCCESS;

bad:
	isccc_sexpr_free(&ack);

	return result;
}

bool
isccc_cc_isack(isccc_sexpr_t *message) {
	isccc_sexpr_t *_ctrl;

	_ctrl = isccc_alist_lookup(message, "_ctrl");
	if (!isccc_alist_alistp(_ctrl)) {
		return false;
	}
	if (isccc_cc_lookupstring(_ctrl, "_ack", NULL) == ISC_R_SUCCESS) {
		return true;
	}
	return false;
}

bool
isccc_cc_isreply(isccc_sexpr_t *message) {
	isccc_sexpr_t *_ctrl;

	_ctrl = isccc_alist_lookup(message, "_ctrl");
	if (!isccc_alist_alistp(_ctrl)) {
		return false;
	}
	if (isccc_cc_lookupstring(_ctrl, "_rpl", NULL) == ISC_R_SUCCESS) {
		return true;
	}
	return false;
}

isc_result_t
isccc_cc_createresponse(isccc_sexpr_t *message, isccc_time_t now,
			isccc_time_t expires, isccc_sexpr_t **alistp) {
	char *_frm, *_to, *type = NULL;
	uint32_t serial;
	isccc_sexpr_t *alist, *_ctrl, *_data;
	isc_result_t result;

	REQUIRE(alistp != NULL && *alistp == NULL);

	_ctrl = isccc_alist_lookup(message, "_ctrl");
	_data = isccc_alist_lookup(message, "_data");
	if (!isccc_alist_alistp(_ctrl) || !isccc_alist_alistp(_data) ||
	    isccc_cc_lookupuint32(_ctrl, "_ser", &serial) != ISC_R_SUCCESS ||
	    isccc_cc_lookupstring(_data, "type", &type) != ISC_R_SUCCESS)
	{
		return ISC_R_FAILURE;
	}
	/*
	 * _frm and _to are optional.
	 */
	_frm = NULL;
	(void)isccc_cc_lookupstring(_ctrl, "_frm", &_frm);
	_to = NULL;
	(void)isccc_cc_lookupstring(_ctrl, "_to", &_to);
	/*
	 * Create the response.
	 */
	alist = NULL;
	result = isccc_cc_createmessage(1, _to, _frm, serial, now, expires,
					&alist);
	if (result != ISC_R_SUCCESS) {
		return result;
	}

	_ctrl = isccc_alist_lookup(alist, "_ctrl");
	if (_ctrl == NULL) {
		result = ISC_R_FAILURE;
		goto bad;
	}

	_data = isccc_alist_lookup(alist, "_data");
	if (_data == NULL) {
		result = ISC_R_FAILURE;
		goto bad;
	}

	if (isccc_cc_definestring(_ctrl, "_rpl", "1") == NULL ||
	    isccc_cc_definestring(_data, "type", type) == NULL)
	{
		result = ISC_R_NOMEMORY;
		goto bad;
	}

	*alistp = alist;

	return ISC_R_SUCCESS;

bad:
	isccc_sexpr_free(&alist);
	return result;
}

isccc_sexpr_t *
isccc_cc_definestring(isccc_sexpr_t *alist, const char *key, const char *str) {
	size_t len;
	isccc_region_t r;

	len = strlen(str);
	r.rstart = UNCONST(str);
	r.rend = r.rstart + len;

	return isccc_alist_definebinary(alist, key, &r);
}

isccc_sexpr_t *
isccc_cc_defineuint32(isccc_sexpr_t *alist, const char *key, uint32_t i) {
	char b[100];
	size_t len;
	isccc_region_t r;

	snprintf(b, sizeof(b), "%u", i);
	len = strlen(b);
	r.rstart = (unsigned char *)b;
	r.rend = (unsigned char *)b + len;

	return isccc_alist_definebinary(alist, key, &r);
}

isc_result_t
isccc_cc_lookupstring(isccc_sexpr_t *alist, const char *key, char **strp) {
	isccc_sexpr_t *kv, *v;

	REQUIRE(strp == NULL || *strp == NULL);

	kv = isccc_alist_assq(alist, key);
	if (kv != NULL) {
		v = ISCCC_SEXPR_CDR(kv);
		if (isccc_sexpr_binaryp(v)) {
			if (strp != NULL) {
				*strp = isccc_sexpr_tostring(v);
			}
			return ISC_R_SUCCESS;
		} else {
			return ISC_R_EXISTS;
		}
	}

	return ISC_R_NOTFOUND;
}

isc_result_t
isccc_cc_lookupuint32(isccc_sexpr_t *alist, const char *key, uint32_t *uintp) {
	isccc_sexpr_t *kv, *v;

	kv = isccc_alist_assq(alist, key);
	if (kv != NULL) {
		v = ISCCC_SEXPR_CDR(kv);
		if (isccc_sexpr_binaryp(v)) {
			if (uintp != NULL) {
				*uintp = (uint32_t)strtoul(
					isccc_sexpr_tostring(v), NULL, 10);
			}
			return ISC_R_SUCCESS;
		} else {
			return ISC_R_EXISTS;
		}
	}

	return ISC_R_NOTFOUND;
}

static void
symtab_undefine(char *key, unsigned int type, isccc_symvalue_t value,
		void *arg) {
	UNUSED(type);
	UNUSED(value);
	UNUSED(arg);

	free(key);
}

static bool
symtab_clean(char *key, unsigned int type, isccc_symvalue_t value, void *arg) {
	isccc_time_t *now;

	UNUSED(key);
	UNUSED(type);

	now = arg;

	if (*now < value.as_uinteger) {
		return false;
	}
	if ((*now - value.as_uinteger) < DUP_LIFETIME) {
		return false;
	}
	return true;
}

isc_result_t
isccc_cc_createsymtab(isccc_symtab_t **symtabp) {
	return isccc_symtab_create(11897, symtab_undefine, NULL, false,
				   symtabp);
}

void
isccc_cc_cleansymtab(isccc_symtab_t *symtab, isccc_time_t now) {
	isccc_symtab_foreach(symtab, symtab_clean, &now);
}

static bool
has_whitespace(const char *str) {
	char c;

	if (str == NULL) {
		return false;
	}
	while ((c = *str++) != '\0') {
		if (c == ' ' || c == '\t' || c == '\n') {
			return true;
		}
	}
	return false;
}

isc_result_t
isccc_cc_checkdup(isccc_symtab_t *symtab, isccc_sexpr_t *message,
		  isccc_time_t now) {
	const char *_frm;
	const char *_to;
	char *_ser = NULL, *_tim = NULL, *tmp;
	isc_result_t result;
	char *key;
	size_t len;
	isccc_symvalue_t value;
	isccc_sexpr_t *_ctrl;

	_ctrl = isccc_alist_lookup(message, "_ctrl");
	if (!isccc_alist_alistp(_ctrl) ||
	    isccc_cc_lookupstring(_ctrl, "_ser", &_ser) != ISC_R_SUCCESS ||
	    isccc_cc_lookupstring(_ctrl, "_tim", &_tim) != ISC_R_SUCCESS)
	{
		return ISC_R_FAILURE;
	}

	INSIST(_ser != NULL);
	INSIST(_tim != NULL);

	/*
	 * _frm and _to are optional.
	 */
	tmp = NULL;
	if (isccc_cc_lookupstring(_ctrl, "_frm", &tmp) != ISC_R_SUCCESS) {
		_frm = "";
	} else {
		_frm = tmp;
		INSIST(_frm != NULL);
	}
	tmp = NULL;
	if (isccc_cc_lookupstring(_ctrl, "_to", &tmp) != ISC_R_SUCCESS) {
		_to = "";
	} else {
		_to = tmp;
		INSIST(_to != NULL);
	}
	/*
	 * Ensure there is no newline in any of the strings.  This is so
	 * we can write them to a file later.
	 */
	if (has_whitespace(_frm) || has_whitespace(_to) ||
	    has_whitespace(_ser) || has_whitespace(_tim))
	{
		return ISC_R_FAILURE;
	}
	len = strlen(_frm) + strlen(_to) + strlen(_ser) + strlen(_tim) + 4;
	key = malloc(len);
	if (key == NULL) {
		return ISC_R_NOMEMORY;
	}
	snprintf(key, len, "%s;%s;%s;%s", _frm, _to, _ser, _tim);
	value.as_uinteger = now;
	result = isccc_symtab_define(symtab, key, ISCCC_SYMTYPE_CCDUP, value,
				     isccc_symexists_reject);
	if (result != ISC_R_SUCCESS) {
		free(key);
		return result;
	}

	return ISC_R_SUCCESS;
}