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/* $OpenBSD: cms.c,v 1.6 2019/11/29 05:14:11 benno Exp $ */
/*
* Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
*
* Permission to use, copy, modify, and 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 THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR 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.
*/
#include <assert.h>
#include <err.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <openssl/cms.h>
#include "extern.h"
/*
* Parse and validate a self-signed CMS message, where the signing X509
* certificate has been hashed to dgst (optional).
* Conforms to RFC 6488.
* The eContentType of the message must be an oid object.
* Return the eContent as a string and set "rsz" to be its length.
*/
unsigned char *
cms_parse_validate(X509 **xp, const char *fn,
const char *oid, const unsigned char *dgst, size_t *rsz)
{
const ASN1_OBJECT *obj;
ASN1_OCTET_STRING **os = NULL;
BIO *bio = NULL, *shamd;
CMS_ContentInfo *cms;
char buf[128], mdbuf[EVP_MAX_MD_SIZE];
int rc = 0, sz;
STACK_OF(X509) *certs = NULL;
EVP_MD *md;
unsigned char *res = NULL;
*rsz = 0;
*xp = NULL;
/*
* This is usually fopen() failure, so let it pass through to
* the handler, which will in turn ignore the entity.
*/
if ((bio = BIO_new_file(fn, "rb")) == NULL) {
if (verbose > 0)
cryptowarnx("%s: BIO_new_file", fn);
return NULL;
}
/*
* If we have a digest specified, create an MD chain that will
* automatically compute a digest during the CMS creation.
*/
if (dgst != NULL) {
if ((shamd = BIO_new(BIO_f_md())) == NULL)
cryptoerrx("BIO_new");
if (!BIO_set_md(shamd, EVP_sha256()))
cryptoerrx("BIO_set_md");
if ((bio = BIO_push(shamd, bio)) == NULL)
cryptoerrx("BIO_push");
}
if ((cms = d2i_CMS_bio(bio, NULL)) == NULL) {
cryptowarnx("%s: RFC 6488: failed CMS parse", fn);
goto out;
}
/*
* If we have a digest, find it in the chain (we'll already have
* made it, so assert otherwise) and verify it.
*/
if (dgst != NULL) {
shamd = BIO_find_type(bio, BIO_TYPE_MD);
assert(shamd != NULL);
if (!BIO_get_md(shamd, &md))
cryptoerrx("BIO_get_md");
assert(EVP_MD_type(md) == NID_sha256);
if ((sz = BIO_gets(shamd, mdbuf, EVP_MAX_MD_SIZE)) < 0)
cryptoerrx("BIO_gets");
assert(sz == SHA256_DIGEST_LENGTH);
if (memcmp(mdbuf, dgst, SHA256_DIGEST_LENGTH)) {
warnx("%s: RFC 6488: bad message digest", fn);
goto out;
}
}
/*
* The CMS is self-signed with a signing certifiate.
* Verify that the self-signage is correct.
*/
if (!CMS_verify(cms, NULL, NULL,
NULL, NULL, CMS_NO_SIGNER_CERT_VERIFY)) {
cryptowarnx("%s: RFC 6488: CMS not self-signed", fn);
goto out;
}
/* RFC 6488 section 2.1.3.1: check the object's eContentType. */
obj = CMS_get0_eContentType(cms);
if ((sz = OBJ_obj2txt(buf, sizeof(buf), obj, 1)) < 0)
cryptoerrx("OBJ_obj2txt");
if ((size_t)sz >= sizeof(buf)) {
warnx("%s: RFC 6488 section 2.1.3.1: "
"eContentType: OID too long", fn);
goto out;
} else if (strcmp(buf, oid)) {
warnx("%s: RFC 6488 section 2.1.3.1: eContentType: "
"unknown OID: %s, want %s", fn, buf, oid);
goto out;
}
/*
* The self-signing certificate is further signed by the input
* signing authority according to RFC 6488, 2.1.4.
* We extract that certificate now for later verification.
*/
certs = CMS_get0_signers(cms);
if (certs == NULL || sk_X509_num(certs) != 1) {
warnx("%s: RFC 6488 section 2.1.4: eContent: "
"want 1 signer, have %d", fn, sk_X509_num(certs));
goto out;
}
*xp = X509_dup(sk_X509_value(certs, 0));
/* Verify that we have eContent to disseminate. */
if ((os = CMS_get0_content(cms)) == NULL || *os == NULL) {
warnx("%s: RFC 6488 section 2.1.4: "
"eContent: zero-length content", fn);
goto out;
}
/*
* Extract and duplicate the eContent.
* The CMS framework offers us no other way of easily managing
* this information; and since we're going to d2i it anyway,
* simply pass it as the desired underlying types.
*/
if ((res = malloc((*os)->length)) == NULL)
err(1, NULL);
memcpy(res, (*os)->data, (*os)->length);
*rsz = (*os)->length;
rc = 1;
out:
BIO_free_all(bio);
sk_X509_free(certs);
CMS_ContentInfo_free(cms);
if (rc == 0) {
X509_free(*xp);
*xp = NULL;
}
return res;
}
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