Adding upstream version 1:9.6p1.upstream/1%9.6p1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1386 insertions, 0 deletions

diff --git a/krl.c b/krl.c
new file mode 100644
index 0000000..e2efdf0
--- /dev/null
+++ b/krl.c
@@ -0,0 +1,1386 @@
+/* $OpenBSD: krl.c,v 1.59 2023/07/17 05:22:30 djm Exp $ */
+/*
+ * Copyright (c) 2012 Damien Miller <djm@mindrot.org>
+ *
+ * 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 "includes.h"
+
+#include <sys/types.h>
+#include <openbsd-compat/sys-tree.h>
+#include <openbsd-compat/sys-queue.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "sshbuf.h"
+#include "ssherr.h"
+#include "sshkey.h"
+#include "authfile.h"
+#include "misc.h"
+#include "log.h"
+#include "digest.h"
+#include "bitmap.h"
+#include "utf8.h"
+
+#include "krl.h"
+
+/* #define DEBUG_KRL */
+#ifdef DEBUG_KRL
+# define KRL_DBG(x) debug3_f x
+#else
+# define KRL_DBG(x)
+#endif
+
+/*
+ * Trees of revoked serial numbers, key IDs and keys. This allows
+ * quick searching, querying and producing lists in canonical order.
+ */
+
+/* Tree of serial numbers. XXX make smarter: really need a real sparse bitmap */
+struct revoked_serial {
+	u_int64_t lo, hi;
+	RB_ENTRY(revoked_serial) tree_entry;
+};
+static int serial_cmp(struct revoked_serial *a, struct revoked_serial *b);
+RB_HEAD(revoked_serial_tree, revoked_serial);
+RB_GENERATE_STATIC(revoked_serial_tree, revoked_serial, tree_entry, serial_cmp)
+
+/* Tree of key IDs */
+struct revoked_key_id {
+	char *key_id;
+	RB_ENTRY(revoked_key_id) tree_entry;
+};
+static int key_id_cmp(struct revoked_key_id *a, struct revoked_key_id *b);
+RB_HEAD(revoked_key_id_tree, revoked_key_id);
+RB_GENERATE_STATIC(revoked_key_id_tree, revoked_key_id, tree_entry, key_id_cmp)
+
+/* Tree of blobs (used for keys and fingerprints) */
+struct revoked_blob {
+	u_char *blob;
+	size_t len;
+	RB_ENTRY(revoked_blob) tree_entry;
+};
+static int blob_cmp(struct revoked_blob *a, struct revoked_blob *b);
+RB_HEAD(revoked_blob_tree, revoked_blob);
+RB_GENERATE_STATIC(revoked_blob_tree, revoked_blob, tree_entry, blob_cmp)
+
+/* Tracks revoked certs for a single CA */
+struct revoked_certs {
+	struct sshkey *ca_key;
+	struct revoked_serial_tree revoked_serials;
+	struct revoked_key_id_tree revoked_key_ids;
+	TAILQ_ENTRY(revoked_certs) entry;
+};
+TAILQ_HEAD(revoked_certs_list, revoked_certs);
+
+struct ssh_krl {
+	u_int64_t krl_version;
+	u_int64_t generated_date;
+	u_int64_t flags;
+	char *comment;
+	struct revoked_blob_tree revoked_keys;
+	struct revoked_blob_tree revoked_sha1s;
+	struct revoked_blob_tree revoked_sha256s;
+	struct revoked_certs_list revoked_certs;
+};
+
+/* Return equal if a and b overlap */
+static int
+serial_cmp(struct revoked_serial *a, struct revoked_serial *b)
+{
+	if (a->hi >= b->lo && a->lo <= b->hi)
+		return 0;
+	return a->lo < b->lo ? -1 : 1;
+}
+
+static int
+key_id_cmp(struct revoked_key_id *a, struct revoked_key_id *b)
+{
+	return strcmp(a->key_id, b->key_id);
+}
+
+static int
+blob_cmp(struct revoked_blob *a, struct revoked_blob *b)
+{
+	int r;
+
+	if (a->len != b->len) {
+		if ((r = memcmp(a->blob, b->blob, MINIMUM(a->len, b->len))) != 0)
+			return r;
+		return a->len > b->len ? 1 : -1;
+	} else
+		return memcmp(a->blob, b->blob, a->len);
+}
+
+struct ssh_krl *
+ssh_krl_init(void)
+{
+	struct ssh_krl *krl;
+
+	if ((krl = calloc(1, sizeof(*krl))) == NULL)
+		return NULL;
+	RB_INIT(&krl->revoked_keys);
+	RB_INIT(&krl->revoked_sha1s);
+	RB_INIT(&krl->revoked_sha256s);
+	TAILQ_INIT(&krl->revoked_certs);
+	return krl;
+}
+
+static void
+revoked_certs_free(struct revoked_certs *rc)
+{
+	struct revoked_serial *rs, *trs;
+	struct revoked_key_id *rki, *trki;
+
+	RB_FOREACH_SAFE(rs, revoked_serial_tree, &rc->revoked_serials, trs) {
+		RB_REMOVE(revoked_serial_tree, &rc->revoked_serials, rs);
+		free(rs);
+	}
+	RB_FOREACH_SAFE(rki, revoked_key_id_tree, &rc->revoked_key_ids, trki) {
+		RB_REMOVE(revoked_key_id_tree, &rc->revoked_key_ids, rki);
+		free(rki->key_id);
+		free(rki);
+	}
+	sshkey_free(rc->ca_key);
+}
+
+void
+ssh_krl_free(struct ssh_krl *krl)
+{
+	struct revoked_blob *rb, *trb;
+	struct revoked_certs *rc, *trc;
+
+	if (krl == NULL)
+		return;
+
+	free(krl->comment);
+	RB_FOREACH_SAFE(rb, revoked_blob_tree, &krl->revoked_keys, trb) {
+		RB_REMOVE(revoked_blob_tree, &krl->revoked_keys, rb);
+		free(rb->blob);
+		free(rb);
+	}
+	RB_FOREACH_SAFE(rb, revoked_blob_tree, &krl->revoked_sha1s, trb) {
+		RB_REMOVE(revoked_blob_tree, &krl->revoked_sha1s, rb);
+		free(rb->blob);
+		free(rb);
+	}
+	RB_FOREACH_SAFE(rb, revoked_blob_tree, &krl->revoked_sha256s, trb) {
+		RB_REMOVE(revoked_blob_tree, &krl->revoked_sha256s, rb);
+		free(rb->blob);
+		free(rb);
+	}
+	TAILQ_FOREACH_SAFE(rc, &krl->revoked_certs, entry, trc) {
+		TAILQ_REMOVE(&krl->revoked_certs, rc, entry);
+		revoked_certs_free(rc);
+	}
+	free(krl);
+}
+
+void
+ssh_krl_set_version(struct ssh_krl *krl, u_int64_t version)
+{
+	krl->krl_version = version;
+}
+
+int
+ssh_krl_set_comment(struct ssh_krl *krl, const char *comment)
+{
+	free(krl->comment);
+	if ((krl->comment = strdup(comment)) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	return 0;
+}
+
+/*
+ * Find the revoked_certs struct for a CA key. If allow_create is set then
+ * create a new one in the tree if one did not exist already.
+ */
+static int
+revoked_certs_for_ca_key(struct ssh_krl *krl, const struct sshkey *ca_key,
+    struct revoked_certs **rcp, int allow_create)
+{
+	struct revoked_certs *rc;
+	int r;
+
+	*rcp = NULL;
+	TAILQ_FOREACH(rc, &krl->revoked_certs, entry) {
+		if ((ca_key == NULL && rc->ca_key == NULL) ||
+		    sshkey_equal(rc->ca_key, ca_key)) {
+			*rcp = rc;
+			return 0;
+		}
+	}
+	if (!allow_create)
+		return 0;
+	/* If this CA doesn't exist in the list then add it now */
+	if ((rc = calloc(1, sizeof(*rc))) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if (ca_key == NULL)
+		rc->ca_key = NULL;
+	else if ((r = sshkey_from_private(ca_key, &rc->ca_key)) != 0) {
+		free(rc);
+		return r;
+	}
+	RB_INIT(&rc->revoked_serials);
+	RB_INIT(&rc->revoked_key_ids);
+	TAILQ_INSERT_TAIL(&krl->revoked_certs, rc, entry);
+	KRL_DBG(("new CA %s", ca_key == NULL ? "*" : sshkey_type(ca_key)));
+	*rcp = rc;
+	return 0;
+}
+
+static int
+insert_serial_range(struct revoked_serial_tree *rt, u_int64_t lo, u_int64_t hi)
+{
+	struct revoked_serial rs, *ers, *crs, *irs;
+
+	KRL_DBG(("insert %llu:%llu", lo, hi));
+	memset(&rs, 0, sizeof(rs));
+	rs.lo = lo;
+	rs.hi = hi;
+	ers = RB_NFIND(revoked_serial_tree, rt, &rs);
+	if (ers == NULL || serial_cmp(ers, &rs) != 0) {
+		/* No entry matches. Just insert */
+		if ((irs = malloc(sizeof(rs))) == NULL)
+			return SSH_ERR_ALLOC_FAIL;
+		memcpy(irs, &rs, sizeof(*irs));
+		ers = RB_INSERT(revoked_serial_tree, rt, irs);
+		if (ers != NULL) {
+			KRL_DBG(("bad: ers != NULL"));
+			/* Shouldn't happen */
+			free(irs);
+			return SSH_ERR_INTERNAL_ERROR;
+		}
+		ers = irs;
+	} else {
+		KRL_DBG(("overlap found %llu:%llu", ers->lo, ers->hi));
+		/*
+		 * The inserted entry overlaps an existing one. Grow the
+		 * existing entry.
+		 */
+		if (ers->lo > lo)
+			ers->lo = lo;
+		if (ers->hi < hi)
+			ers->hi = hi;
+	}
+
+	/*
+	 * The inserted or revised range might overlap or abut adjacent ones;
+	 * coalesce as necessary.
+	 */
+
+	/* Check predecessors */
+	while ((crs = RB_PREV(revoked_serial_tree, rt, ers)) != NULL) {
+		KRL_DBG(("pred %llu:%llu", crs->lo, crs->hi));
+		if (ers->lo != 0 && crs->hi < ers->lo - 1)
+			break;
+		/* This entry overlaps. */
+		if (crs->lo < ers->lo) {
+			ers->lo = crs->lo;
+			KRL_DBG(("pred extend %llu:%llu", ers->lo, ers->hi));
+		}
+		RB_REMOVE(revoked_serial_tree, rt, crs);
+		free(crs);
+	}
+	/* Check successors */
+	while ((crs = RB_NEXT(revoked_serial_tree, rt, ers)) != NULL) {
+		KRL_DBG(("succ %llu:%llu", crs->lo, crs->hi));
+		if (ers->hi != (u_int64_t)-1 && crs->lo > ers->hi + 1)
+			break;
+		/* This entry overlaps. */
+		if (crs->hi > ers->hi) {
+			ers->hi = crs->hi;
+			KRL_DBG(("succ extend %llu:%llu", ers->lo, ers->hi));
+		}
+		RB_REMOVE(revoked_serial_tree, rt, crs);
+		free(crs);
+	}
+	KRL_DBG(("done, final %llu:%llu", ers->lo, ers->hi));
+	return 0;
+}
+
+int
+ssh_krl_revoke_cert_by_serial(struct ssh_krl *krl, const struct sshkey *ca_key,
+    u_int64_t serial)
+{
+	return ssh_krl_revoke_cert_by_serial_range(krl, ca_key, serial, serial);
+}
+
+int
+ssh_krl_revoke_cert_by_serial_range(struct ssh_krl *krl,
+    const struct sshkey *ca_key, u_int64_t lo, u_int64_t hi)
+{
+	struct revoked_certs *rc;
+	int r;
+
+	if (lo > hi || lo == 0)
+		return SSH_ERR_INVALID_ARGUMENT;
+	if ((r = revoked_certs_for_ca_key(krl, ca_key, &rc, 1)) != 0)
+		return r;
+	return insert_serial_range(&rc->revoked_serials, lo, hi);
+}
+
+int
+ssh_krl_revoke_cert_by_key_id(struct ssh_krl *krl, const struct sshkey *ca_key,
+    const char *key_id)
+{
+	struct revoked_key_id *rki, *erki;
+	struct revoked_certs *rc;
+	int r;
+
+	if ((r = revoked_certs_for_ca_key(krl, ca_key, &rc, 1)) != 0)
+		return r;
+
+	KRL_DBG(("revoke %s", key_id));
+	if ((rki = calloc(1, sizeof(*rki))) == NULL ||
+	    (rki->key_id = strdup(key_id)) == NULL) {
+		free(rki);
+		return SSH_ERR_ALLOC_FAIL;
+	}
+	erki = RB_INSERT(revoked_key_id_tree, &rc->revoked_key_ids, rki);
+	if (erki != NULL) {
+		free(rki->key_id);
+		free(rki);
+	}
+	return 0;
+}
+
+/* Convert "key" to a public key blob without any certificate information */
+static int
+plain_key_blob(const struct sshkey *key, u_char **blob, size_t *blen)
+{
+	struct sshkey *kcopy;
+	int r;
+
+	if ((r = sshkey_from_private(key, &kcopy)) != 0)
+		return r;
+	if (sshkey_is_cert(kcopy)) {
+		if ((r = sshkey_drop_cert(kcopy)) != 0) {
+			sshkey_free(kcopy);
+			return r;
+		}
+	}
+	r = sshkey_to_blob(kcopy, blob, blen);
+	sshkey_free(kcopy);
+	return r;
+}
+
+/* Revoke a key blob. Ownership of blob is transferred to the tree */
+static int
+revoke_blob(struct revoked_blob_tree *rbt, u_char *blob, size_t len)
+{
+	struct revoked_blob *rb, *erb;
+
+	if ((rb = calloc(1, sizeof(*rb))) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	rb->blob = blob;
+	rb->len = len;
+	erb = RB_INSERT(revoked_blob_tree, rbt, rb);
+	if (erb != NULL) {
+		free(rb->blob);
+		free(rb);
+	}
+	return 0;
+}
+
+int
+ssh_krl_revoke_key_explicit(struct ssh_krl *krl, const struct sshkey *key)
+{
+	u_char *blob;
+	size_t len;
+	int r;
+
+	debug3_f("revoke type %s", sshkey_type(key));
+	if ((r = plain_key_blob(key, &blob, &len)) != 0)
+		return r;
+	return revoke_blob(&krl->revoked_keys, blob, len);
+}
+
+static int
+revoke_by_hash(struct revoked_blob_tree *target, const u_char *p, size_t len)
+{
+	u_char *blob;
+	int r;
+
+	/* need to copy hash, as revoke_blob steals ownership */
+	if ((blob = malloc(len)) == NULL)
+		return SSH_ERR_SYSTEM_ERROR;
+	memcpy(blob, p, len);
+	if ((r = revoke_blob(target, blob, len)) != 0) {
+		free(blob);
+		return r;
+	}
+	return 0;
+}
+
+int
+ssh_krl_revoke_key_sha1(struct ssh_krl *krl, const u_char *p, size_t len)
+{
+	debug3_f("revoke by sha1");
+	if (len != 20)
+		return SSH_ERR_INVALID_FORMAT;
+	return revoke_by_hash(&krl->revoked_sha1s, p, len);
+}
+
+int
+ssh_krl_revoke_key_sha256(struct ssh_krl *krl, const u_char *p, size_t len)
+{
+	debug3_f("revoke by sha256");
+	if (len != 32)
+		return SSH_ERR_INVALID_FORMAT;
+	return revoke_by_hash(&krl->revoked_sha256s, p, len);
+}
+
+int
+ssh_krl_revoke_key(struct ssh_krl *krl, const struct sshkey *key)
+{
+	/* XXX replace with SHA256? */
+	if (!sshkey_is_cert(key))
+		return ssh_krl_revoke_key_explicit(krl, key);
+
+	if (key->cert->serial == 0) {
+		return ssh_krl_revoke_cert_by_key_id(krl,
+		    key->cert->signature_key,
+		    key->cert->key_id);
+	} else {
+		return ssh_krl_revoke_cert_by_serial(krl,
+		    key->cert->signature_key,
+		    key->cert->serial);
+	}
+}
+
+/*
+ * Select the most compact section type to emit next in a KRL based on
+ * the current section type, the run length of contiguous revoked serial
+ * numbers and the gaps from the last and to the next revoked serial.
+ * Applies a mostly-accurate bit cost model to select the section type
+ * that will minimise the size of the resultant KRL.
+ */
+static int
+choose_next_state(int current_state, u_int64_t contig, int final,
+    u_int64_t last_gap, u_int64_t next_gap, int *force_new_section)
+{
+	int new_state;
+	u_int64_t cost, cost_list, cost_range, cost_bitmap, cost_bitmap_restart;
+
+	/*
+	 * Avoid unsigned overflows.
+	 * The limits are high enough to avoid confusing the calculations.
+	 */
+	contig = MINIMUM(contig, 1ULL<<31);
+	last_gap = MINIMUM(last_gap, 1ULL<<31);
+	next_gap = MINIMUM(next_gap, 1ULL<<31);
+
+	/*
+	 * Calculate the cost to switch from the current state to candidates.
+	 * NB. range sections only ever contain a single range, so their
+	 * switching cost is independent of the current_state.
+	 */
+	cost_list = cost_bitmap = cost_bitmap_restart = 0;
+	cost_range = 8;
+	switch (current_state) {
+	case KRL_SECTION_CERT_SERIAL_LIST:
+		cost_bitmap_restart = cost_bitmap = 8 + 64;
+		break;
+	case KRL_SECTION_CERT_SERIAL_BITMAP:
+		cost_list = 8;
+		cost_bitmap_restart = 8 + 64;
+		break;
+	case KRL_SECTION_CERT_SERIAL_RANGE:
+	case 0:
+		cost_bitmap_restart = cost_bitmap = 8 + 64;
+		cost_list = 8;
+	}
+
+	/* Estimate base cost in bits of each section type */
+	cost_list += 64 * contig + (final ? 0 : 8+64);
+	cost_range += (2 * 64) + (final ? 0 : 8+64);
+	cost_bitmap += last_gap + contig + (final ? 0 : MINIMUM(next_gap, 8+64));
+	cost_bitmap_restart += contig + (final ? 0 : MINIMUM(next_gap, 8+64));
+
+	/* Convert to byte costs for actual comparison */
+	cost_list = (cost_list + 7) / 8;
+	cost_bitmap = (cost_bitmap + 7) / 8;
+	cost_bitmap_restart = (cost_bitmap_restart + 7) / 8;
+	cost_range = (cost_range + 7) / 8;
+
+	/* Now pick the best choice */
+	*force_new_section = 0;
+	new_state = KRL_SECTION_CERT_SERIAL_BITMAP;
+	cost = cost_bitmap;
+	if (cost_range < cost) {
+		new_state = KRL_SECTION_CERT_SERIAL_RANGE;
+		cost = cost_range;
+	}
+	if (cost_list < cost) {
+		new_state = KRL_SECTION_CERT_SERIAL_LIST;
+		cost = cost_list;
+	}
+	if (cost_bitmap_restart < cost) {
+		new_state = KRL_SECTION_CERT_SERIAL_BITMAP;
+		*force_new_section = 1;
+		cost = cost_bitmap_restart;
+	}
+	KRL_DBG(("contig %llu last_gap %llu next_gap %llu final %d, costs:"
+	    "list %llu range %llu bitmap %llu new bitmap %llu, "
+	    "selected 0x%02x%s", (long long unsigned)contig,
+	    (long long unsigned)last_gap, (long long unsigned)next_gap, final,
+	    (long long unsigned)cost_list, (long long unsigned)cost_range,
+	    (long long unsigned)cost_bitmap,
+	    (long long unsigned)cost_bitmap_restart, new_state,
+	    *force_new_section ? " restart" : ""));
+	return new_state;
+}
+
+static int
+put_bitmap(struct sshbuf *buf, struct bitmap *bitmap)
+{
+	size_t len;
+	u_char *blob;
+	int r;
+
+	len = bitmap_nbytes(bitmap);
+	if ((blob = malloc(len)) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+	if (bitmap_to_string(bitmap, blob, len) != 0) {
+		free(blob);
+		return SSH_ERR_INTERNAL_ERROR;
+	}
+	r = sshbuf_put_bignum2_bytes(buf, blob, len);
+	free(blob);
+	return r;
+}
+
+/* Generate a KRL_SECTION_CERTIFICATES KRL section */
+static int
+revoked_certs_generate(struct revoked_certs *rc, struct sshbuf *buf)
+{
+	int final, force_new_sect, r = SSH_ERR_INTERNAL_ERROR;
+	u_int64_t i, contig, gap, last = 0, bitmap_start = 0;
+	struct revoked_serial *rs, *nrs;
+	struct revoked_key_id *rki;
+	int next_state, state = 0;
+	struct sshbuf *sect;
+	struct bitmap *bitmap = NULL;
+
+	if ((sect = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+
+	/* Store the header: optional CA scope key, reserved */
+	if (rc->ca_key == NULL) {
+		if ((r = sshbuf_put_string(buf, NULL, 0)) != 0)
+			goto out;
+	} else {
+		if ((r = sshkey_puts(rc->ca_key, buf)) != 0)
+			goto out;
+	}
+	if ((r = sshbuf_put_string(buf, NULL, 0)) != 0)
+		goto out;
+
+	/* Store the revoked serials.  */
+	for (rs = RB_MIN(revoked_serial_tree, &rc->revoked_serials);
+	     rs != NULL;
+	     rs = RB_NEXT(revoked_serial_tree, &rc->revoked_serials, rs)) {
+		KRL_DBG(("serial %llu:%llu state 0x%02x",
+		    (long long unsigned)rs->lo, (long long unsigned)rs->hi,
+		    state));
+
+		/* Check contiguous length and gap to next section (if any) */
+		nrs = RB_NEXT(revoked_serial_tree, &rc->revoked_serials, rs);
+		final = nrs == NULL;
+		gap = nrs == NULL ? 0 : nrs->lo - rs->hi;
+		contig = 1 + (rs->hi - rs->lo);
+
+		/* Choose next state based on these */
+		next_state = choose_next_state(state, contig, final,
+		    state == 0 ? 0 : rs->lo - last, gap, &force_new_sect);
+
+		/*
+		 * If the current section is a range section or has a different
+		 * type to the next section, then finish it off now.
+		 */
+		if (state != 0 && (force_new_sect || next_state != state ||
+		    state == KRL_SECTION_CERT_SERIAL_RANGE)) {
+			KRL_DBG(("finish state 0x%02x", state));
+			switch (state) {
+			case KRL_SECTION_CERT_SERIAL_LIST:
+			case KRL_SECTION_CERT_SERIAL_RANGE:
+				break;
+			case KRL_SECTION_CERT_SERIAL_BITMAP:
+				if ((r = put_bitmap(sect, bitmap)) != 0)
+					goto out;
+				bitmap_free(bitmap);
+				bitmap = NULL;
+				break;
+			}
+			if ((r = sshbuf_put_u8(buf, state)) != 0 ||
+			    (r = sshbuf_put_stringb(buf, sect)) != 0)
+				goto out;
+			sshbuf_reset(sect);
+		}
+
+		/* If we are starting a new section then prepare it now */
+		if (next_state != state || force_new_sect) {
+			KRL_DBG(("start state 0x%02x",
+			    next_state));
+			state = next_state;
+			sshbuf_reset(sect);
+			switch (state) {
+			case KRL_SECTION_CERT_SERIAL_LIST:
+			case KRL_SECTION_CERT_SERIAL_RANGE:
+				break;
+			case KRL_SECTION_CERT_SERIAL_BITMAP:
+				if ((bitmap = bitmap_new()) == NULL) {
+					r = SSH_ERR_ALLOC_FAIL;
+					goto out;
+				}
+				bitmap_start = rs->lo;
+				if ((r = sshbuf_put_u64(sect,
+				    bitmap_start)) != 0)
+					goto out;
+				break;
+			}
+		}
+
+		/* Perform section-specific processing */
+		switch (state) {
+		case KRL_SECTION_CERT_SERIAL_LIST:
+			for (i = 0; i < contig; i++) {
+				if ((r = sshbuf_put_u64(sect, rs->lo + i)) != 0)
+					goto out;
+			}
+			break;
+		case KRL_SECTION_CERT_SERIAL_RANGE:
+			if ((r = sshbuf_put_u64(sect, rs->lo)) != 0 ||
+			    (r = sshbuf_put_u64(sect, rs->hi)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_CERT_SERIAL_BITMAP:
+			if (rs->lo - bitmap_start > INT_MAX) {
+				error_f("insane bitmap gap");
+				goto out;
+			}
+			for (i = 0; i < contig; i++) {
+				if (bitmap_set_bit(bitmap,
+				    rs->lo + i - bitmap_start) != 0) {
+					r = SSH_ERR_ALLOC_FAIL;
+					goto out;
+				}
+			}
+			break;
+		}
+		last = rs->hi;
+	}
+	/* Flush the remaining section, if any */
+	if (state != 0) {
+		KRL_DBG(("serial final flush for state 0x%02x", state));
+		switch (state) {
+		case KRL_SECTION_CERT_SERIAL_LIST:
+		case KRL_SECTION_CERT_SERIAL_RANGE:
+			break;
+		case KRL_SECTION_CERT_SERIAL_BITMAP:
+			if ((r = put_bitmap(sect, bitmap)) != 0)
+				goto out;
+			bitmap_free(bitmap);
+			bitmap = NULL;
+			break;
+		}
+		if ((r = sshbuf_put_u8(buf, state)) != 0 ||
+		    (r = sshbuf_put_stringb(buf, sect)) != 0)
+			goto out;
+	}
+	KRL_DBG(("serial done "));
+
+	/* Now output a section for any revocations by key ID */
+	sshbuf_reset(sect);
+	RB_FOREACH(rki, revoked_key_id_tree, &rc->revoked_key_ids) {
+		KRL_DBG(("key ID %s", rki->key_id));
+		if ((r = sshbuf_put_cstring(sect, rki->key_id)) != 0)
+			goto out;
+	}
+	if (sshbuf_len(sect) != 0) {
+		if ((r = sshbuf_put_u8(buf, KRL_SECTION_CERT_KEY_ID)) != 0 ||
+		    (r = sshbuf_put_stringb(buf, sect)) != 0)
+			goto out;
+	}
+	r = 0;
+ out:
+	bitmap_free(bitmap);
+	sshbuf_free(sect);
+	return r;
+}
+
+int
+ssh_krl_to_blob(struct ssh_krl *krl, struct sshbuf *buf)
+{
+	int r = SSH_ERR_INTERNAL_ERROR;
+	struct revoked_certs *rc;
+	struct revoked_blob *rb;
+	struct sshbuf *sect;
+	u_char *sblob = NULL;
+
+	if (krl->generated_date == 0)
+		krl->generated_date = time(NULL);
+
+	if ((sect = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+
+	/* Store the header */
+	if ((r = sshbuf_put(buf, KRL_MAGIC, sizeof(KRL_MAGIC) - 1)) != 0 ||
+	    (r = sshbuf_put_u32(buf, KRL_FORMAT_VERSION)) != 0 ||
+	    (r = sshbuf_put_u64(buf, krl->krl_version)) != 0 ||
+	    (r = sshbuf_put_u64(buf, krl->generated_date)) != 0 ||
+	    (r = sshbuf_put_u64(buf, krl->flags)) != 0 ||
+	    (r = sshbuf_put_string(buf, NULL, 0)) != 0 ||
+	    (r = sshbuf_put_cstring(buf, krl->comment)) != 0)
+		goto out;
+
+	/* Store sections for revoked certificates */
+	TAILQ_FOREACH(rc, &krl->revoked_certs, entry) {
+		sshbuf_reset(sect);
+		if ((r = revoked_certs_generate(rc, sect)) != 0)
+			goto out;
+		if ((r = sshbuf_put_u8(buf, KRL_SECTION_CERTIFICATES)) != 0 ||
+		    (r = sshbuf_put_stringb(buf, sect)) != 0)
+			goto out;
+	}
+
+	/* Finally, output sections for revocations by public key/hash */
+	sshbuf_reset(sect);
+	RB_FOREACH(rb, revoked_blob_tree, &krl->revoked_keys) {
+		KRL_DBG(("key len %zu ", rb->len));
+		if ((r = sshbuf_put_string(sect, rb->blob, rb->len)) != 0)
+			goto out;
+	}
+	if (sshbuf_len(sect) != 0) {
+		if ((r = sshbuf_put_u8(buf, KRL_SECTION_EXPLICIT_KEY)) != 0 ||
+		    (r = sshbuf_put_stringb(buf, sect)) != 0)
+			goto out;
+	}
+	sshbuf_reset(sect);
+	RB_FOREACH(rb, revoked_blob_tree, &krl->revoked_sha1s) {
+		KRL_DBG(("hash len %zu ", rb->len));
+		if ((r = sshbuf_put_string(sect, rb->blob, rb->len)) != 0)
+			goto out;
+	}
+	if (sshbuf_len(sect) != 0) {
+		if ((r = sshbuf_put_u8(buf,
+		    KRL_SECTION_FINGERPRINT_SHA1)) != 0 ||
+		    (r = sshbuf_put_stringb(buf, sect)) != 0)
+			goto out;
+	}
+	sshbuf_reset(sect);
+	RB_FOREACH(rb, revoked_blob_tree, &krl->revoked_sha256s) {
+		KRL_DBG(("hash len %zu ", rb->len));
+		if ((r = sshbuf_put_string(sect, rb->blob, rb->len)) != 0)
+			goto out;
+	}
+	if (sshbuf_len(sect) != 0) {
+		if ((r = sshbuf_put_u8(buf,
+		    KRL_SECTION_FINGERPRINT_SHA256)) != 0 ||
+		    (r = sshbuf_put_stringb(buf, sect)) != 0)
+			goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	free(sblob);
+	sshbuf_free(sect);
+	return r;
+}
+
+static void
+format_timestamp(u_int64_t timestamp, char *ts, size_t nts)
+{
+	time_t t;
+	struct tm *tm;
+
+	t = timestamp;
+	tm = localtime(&t);
+	if (tm == NULL)
+		strlcpy(ts, "<INVALID>", nts);
+	else {
+		*ts = '\0';
+		strftime(ts, nts, "%Y%m%dT%H%M%S", tm);
+	}
+}
+
+static int
+cert_extension_subsection(struct sshbuf *subsect, struct ssh_krl *krl)
+{
+	int r = SSH_ERR_INTERNAL_ERROR;
+	u_char critical = 1;
+	struct sshbuf *value = NULL;
+	char *name = NULL;
+
+	if ((r = sshbuf_get_cstring(subsect, &name, NULL)) != 0 ||
+	    (r = sshbuf_get_u8(subsect, &critical)) != 0 ||
+	    (r = sshbuf_froms(subsect, &value)) != 0) {
+		debug_fr(r, "parse");
+		error("KRL has invalid certificate extension subsection");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if (sshbuf_len(subsect) != 0) {
+		error("KRL has invalid certificate extension subsection: "
+		    "trailing data");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	debug_f("cert extension %s critical %u len %zu",
+	    name, critical, sshbuf_len(value));
+	/* no extensions are currently supported */
+	if (critical) {
+		error("KRL contains unsupported critical certificate "
+		    "subsection \"%s\"", name);
+		r = SSH_ERR_FEATURE_UNSUPPORTED;
+		goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	free(name);
+	sshbuf_free(value);
+	return r;
+}
+
+static int
+parse_revoked_certs(struct sshbuf *buf, struct ssh_krl *krl)
+{
+	int r = SSH_ERR_INTERNAL_ERROR;
+	u_char type;
+	const u_char *blob;
+	size_t blen, nbits;
+	struct sshbuf *subsect = NULL;
+	u_int64_t serial, serial_lo, serial_hi;
+	struct bitmap *bitmap = NULL;
+	char *key_id = NULL;
+	struct sshkey *ca_key = NULL;
+
+	if ((subsect = sshbuf_new()) == NULL)
+		return SSH_ERR_ALLOC_FAIL;
+
+	/* Header: key, reserved */
+	if ((r = sshbuf_get_string_direct(buf, &blob, &blen)) != 0 ||
+	    (r = sshbuf_skip_string(buf)) != 0)
+		goto out;
+	if (blen != 0 && (r = sshkey_from_blob(blob, blen, &ca_key)) != 0)
+		goto out;
+
+	while (sshbuf_len(buf) > 0) {
+		sshbuf_free(subsect);
+		subsect = NULL;
+		if ((r = sshbuf_get_u8(buf, &type)) != 0 ||
+		    (r = sshbuf_froms(buf, &subsect)) != 0)
+			goto out;
+		KRL_DBG(("subsection type 0x%02x", type));
+		/* sshbuf_dump(subsect, stderr); */
+
+		switch (type) {
+		case KRL_SECTION_CERT_SERIAL_LIST:
+			while (sshbuf_len(subsect) > 0) {
+				if ((r = sshbuf_get_u64(subsect, &serial)) != 0)
+					goto out;
+				if ((r = ssh_krl_revoke_cert_by_serial(krl,
+				    ca_key, serial)) != 0)
+					goto out;
+			}
+			break;
+		case KRL_SECTION_CERT_SERIAL_RANGE:
+			if ((r = sshbuf_get_u64(subsect, &serial_lo)) != 0 ||
+			    (r = sshbuf_get_u64(subsect, &serial_hi)) != 0)
+				goto out;
+			if ((r = ssh_krl_revoke_cert_by_serial_range(krl,
+			    ca_key, serial_lo, serial_hi)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_CERT_SERIAL_BITMAP:
+			if ((bitmap = bitmap_new()) == NULL) {
+				r = SSH_ERR_ALLOC_FAIL;
+				goto out;
+			}
+			if ((r = sshbuf_get_u64(subsect, &serial_lo)) != 0 ||
+			    (r = sshbuf_get_bignum2_bytes_direct(subsect,
+			    &blob, &blen)) != 0)
+				goto out;
+			if (bitmap_from_string(bitmap, blob, blen) != 0) {
+				r = SSH_ERR_INVALID_FORMAT;
+				goto out;
+			}
+			nbits = bitmap_nbits(bitmap);
+			for (serial = 0; serial < (u_int64_t)nbits; serial++) {
+				if (serial > 0 && serial_lo + serial == 0) {
+					error_f("bitmap wraps u64");
+					r = SSH_ERR_INVALID_FORMAT;
+					goto out;
+				}
+				if (!bitmap_test_bit(bitmap, serial))
+					continue;
+				if ((r = ssh_krl_revoke_cert_by_serial(krl,
+				    ca_key, serial_lo + serial)) != 0)
+					goto out;
+			}
+			bitmap_free(bitmap);
+			bitmap = NULL;
+			break;
+		case KRL_SECTION_CERT_KEY_ID:
+			while (sshbuf_len(subsect) > 0) {
+				if ((r = sshbuf_get_cstring(subsect,
+				    &key_id, NULL)) != 0)
+					goto out;
+				if ((r = ssh_krl_revoke_cert_by_key_id(krl,
+				    ca_key, key_id)) != 0)
+					goto out;
+				free(key_id);
+				key_id = NULL;
+			}
+			break;
+		case KRL_SECTION_CERT_EXTENSION:
+			if ((r = cert_extension_subsection(subsect, krl)) != 0)
+				goto out;
+			break;
+		default:
+			error("Unsupported KRL certificate section %u", type);
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+		if (sshbuf_len(subsect) > 0) {
+			error("KRL certificate section contains unparsed data");
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+	}
+
+	r = 0;
+ out:
+	if (bitmap != NULL)
+		bitmap_free(bitmap);
+	free(key_id);
+	sshkey_free(ca_key);
+	sshbuf_free(subsect);
+	return r;
+}
+
+static int
+blob_section(struct sshbuf *sect, struct revoked_blob_tree *target_tree,
+    size_t expected_len)
+{
+	u_char *rdata = NULL;
+	size_t rlen = 0;
+	int r;
+
+	while (sshbuf_len(sect) > 0) {
+		if ((r = sshbuf_get_string(sect, &rdata, &rlen)) != 0)
+			return r;
+		if (expected_len != 0 && rlen != expected_len) {
+			error_f("bad length");
+			free(rdata);
+			return SSH_ERR_INVALID_FORMAT;
+		}
+		if ((r = revoke_blob(target_tree, rdata, rlen)) != 0) {
+			free(rdata);
+			return r;
+		}
+	}
+	return 0;
+}
+
+static int
+extension_section(struct sshbuf *sect, struct ssh_krl *krl)
+{
+	int r = SSH_ERR_INTERNAL_ERROR;
+	u_char critical = 1;
+	struct sshbuf *value = NULL;
+	char *name = NULL;
+
+	if ((r = sshbuf_get_cstring(sect, &name, NULL)) != 0 ||
+	    (r = sshbuf_get_u8(sect, &critical)) != 0 ||
+	    (r = sshbuf_froms(sect, &value)) != 0) {
+		debug_fr(r, "parse");
+		error("KRL has invalid extension section");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if (sshbuf_len(sect) != 0) {
+		error("KRL has invalid extension section: trailing data");
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	debug_f("extension %s critical %u len %zu",
+	    name, critical, sshbuf_len(value));
+	/* no extensions are currently supported */
+	if (critical) {
+		error("KRL contains unsupported critical section \"%s\"", name);
+		r = SSH_ERR_FEATURE_UNSUPPORTED;
+		goto out;
+	}
+	/* success */
+	r = 0;
+ out:
+	free(name);
+	sshbuf_free(value);
+	return r;
+}
+
+/* Attempt to parse a KRL */
+int
+ssh_krl_from_blob(struct sshbuf *buf, struct ssh_krl **krlp)
+{
+	struct sshbuf *copy = NULL, *sect = NULL;
+	struct ssh_krl *krl = NULL;
+	char timestamp[64];
+	int r = SSH_ERR_INTERNAL_ERROR;
+	u_char type;
+	u_int format_version;
+
+	*krlp = NULL;
+
+	/* KRL must begin with magic string */
+	if ((r = sshbuf_cmp(buf, 0, KRL_MAGIC, sizeof(KRL_MAGIC) - 1)) != 0) {
+		debug2_f("bad KRL magic header");
+		return SSH_ERR_KRL_BAD_MAGIC;
+	}
+
+	if ((krl = ssh_krl_init()) == NULL) {
+		error_f("alloc failed");
+		goto out;
+	}
+	/* Don't modify buffer */
+	if ((copy = sshbuf_fromb(buf)) == NULL) {
+		r = SSH_ERR_ALLOC_FAIL;
+		goto out;
+	}
+	if ((r = sshbuf_consume(copy, sizeof(KRL_MAGIC) - 1)) != 0 ||
+	    (r = sshbuf_get_u32(copy, &format_version)) != 0)
+		goto out;
+	if (format_version != KRL_FORMAT_VERSION) {
+		error_f("unsupported KRL format version %u", format_version);
+		r = SSH_ERR_INVALID_FORMAT;
+		goto out;
+	}
+	if ((r = sshbuf_get_u64(copy, &krl->krl_version)) != 0 ||
+	    (r = sshbuf_get_u64(copy, &krl->generated_date)) != 0 ||
+	    (r = sshbuf_get_u64(copy, &krl->flags)) != 0 ||
+	    (r = sshbuf_skip_string(copy)) != 0 ||
+	    (r = sshbuf_get_cstring(copy, &krl->comment, NULL)) != 0) {
+		error_fr(r, "parse KRL header");
+		goto out;
+	}
+	format_timestamp(krl->generated_date, timestamp, sizeof(timestamp));
+	debug("KRL version %llu generated at %s%s%s",
+	    (long long unsigned)krl->krl_version, timestamp,
+	    *krl->comment ? ": " : "", krl->comment);
+
+	/* Parse and load the KRL sections. */
+	while (sshbuf_len(copy) > 0) {
+		sshbuf_free(sect);
+		sect = NULL;
+		if ((r = sshbuf_get_u8(copy, &type)) != 0 ||
+		    (r = sshbuf_froms(copy, &sect)) != 0)
+			goto out;
+		KRL_DBG(("section 0x%02x", type));
+
+		switch (type) {
+		case KRL_SECTION_CERTIFICATES:
+			if ((r = parse_revoked_certs(sect, krl)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_EXPLICIT_KEY:
+			if ((r = blob_section(sect,
+			    &krl->revoked_keys, 0)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_FINGERPRINT_SHA1:
+			if ((r = blob_section(sect,
+			    &krl->revoked_sha1s, 20)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_FINGERPRINT_SHA256:
+			if ((r = blob_section(sect,
+			    &krl->revoked_sha256s, 32)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_EXTENSION:
+			if ((r = extension_section(sect, krl)) != 0)
+				goto out;
+			break;
+		case KRL_SECTION_SIGNATURE:
+			/* Handled above, but still need to stay in synch */
+			sshbuf_free(sect);
+			sect = NULL;
+			if ((r = sshbuf_skip_string(copy)) != 0)
+				goto out;
+			break;
+		default:
+			error("Unsupported KRL section %u", type);
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+		if (sect != NULL && sshbuf_len(sect) > 0) {
+			error("KRL section contains unparsed data");
+			r = SSH_ERR_INVALID_FORMAT;
+			goto out;
+		}
+	}
+
+	/* Success */
+	*krlp = krl;
+	r = 0;
+ out:
+	if (r != 0)
+		ssh_krl_free(krl);
+	sshbuf_free(copy);
+	sshbuf_free(sect);
+	return r;
+}
+
+/* Checks certificate serial number and key ID revocation */
+static int
+is_cert_revoked(const struct sshkey *key, struct revoked_certs *rc)
+{
+	struct revoked_serial rs, *ers;
+	struct revoked_key_id rki, *erki;
+
+	/* Check revocation by cert key ID */
+	memset(&rki, 0, sizeof(rki));
+	rki.key_id = key->cert->key_id;
+	erki = RB_FIND(revoked_key_id_tree, &rc->revoked_key_ids, &rki);
+	if (erki != NULL) {
+		KRL_DBG(("revoked by key ID"));
+		return SSH_ERR_KEY_REVOKED;
+	}
+
+	/*
+	 * Zero serials numbers are ignored (it's the default when the
+	 * CA doesn't specify one).
+	 */
+	if (key->cert->serial == 0)
+		return 0;
+
+	memset(&rs, 0, sizeof(rs));
+	rs.lo = rs.hi = key->cert->serial;
+	ers = RB_FIND(revoked_serial_tree, &rc->revoked_serials, &rs);
+	if (ers != NULL) {
+		KRL_DBG(("revoked serial %llu matched %llu:%llu",
+		    key->cert->serial, ers->lo, ers->hi));
+		return SSH_ERR_KEY_REVOKED;
+	}
+	return 0;
+}
+
+/* Checks whether a given key/cert is revoked. Does not check its CA */
+static int
+is_key_revoked(struct ssh_krl *krl, const struct sshkey *key)
+{
+	struct revoked_blob rb, *erb;
+	struct revoked_certs *rc;
+	int r;
+
+	/* Check explicitly revoked hashes first */
+	memset(&rb, 0, sizeof(rb));
+	if ((r = sshkey_fingerprint_raw(key, SSH_DIGEST_SHA1,
+	    &rb.blob, &rb.len)) != 0)
+		return r;
+	erb = RB_FIND(revoked_blob_tree, &krl->revoked_sha1s, &rb);
+	free(rb.blob);
+	if (erb != NULL) {
+		KRL_DBG(("revoked by key SHA1"));
+		return SSH_ERR_KEY_REVOKED;
+	}
+	memset(&rb, 0, sizeof(rb));
+	if ((r = sshkey_fingerprint_raw(key, SSH_DIGEST_SHA256,
+	    &rb.blob, &rb.len)) != 0)
+		return r;
+	erb = RB_FIND(revoked_blob_tree, &krl->revoked_sha256s, &rb);
+	free(rb.blob);
+	if (erb != NULL) {
+		KRL_DBG(("revoked by key SHA256"));
+		return SSH_ERR_KEY_REVOKED;
+	}
+
+	/* Next, explicit keys */
+	memset(&rb, 0, sizeof(rb));
+	if ((r = plain_key_blob(key, &rb.blob, &rb.len)) != 0)
+		return r;
+	erb = RB_FIND(revoked_blob_tree, &krl->revoked_keys, &rb);
+	free(rb.blob);
+	if (erb != NULL) {
+		KRL_DBG(("revoked by explicit key"));
+		return SSH_ERR_KEY_REVOKED;
+	}
+
+	if (!sshkey_is_cert(key))
+		return 0;
+
+	/* Check cert revocation for the specified CA */
+	if ((r = revoked_certs_for_ca_key(krl, key->cert->signature_key,
+	    &rc, 0)) != 0)
+		return r;
+	if (rc != NULL) {
+		if ((r = is_cert_revoked(key, rc)) != 0)
+			return r;
+	}
+	/* Check cert revocation for the wildcard CA */
+	if ((r = revoked_certs_for_ca_key(krl, NULL, &rc, 0)) != 0)
+		return r;
+	if (rc != NULL) {
+		if ((r = is_cert_revoked(key, rc)) != 0)
+			return r;
+	}
+
+	KRL_DBG(("%llu no match", key->cert->serial));
+	return 0;
+}
+
+int
+ssh_krl_check_key(struct ssh_krl *krl, const struct sshkey *key)
+{
+	int r;
+
+	KRL_DBG(("checking key"));
+	if ((r = is_key_revoked(krl, key)) != 0)
+		return r;
+	if (sshkey_is_cert(key)) {
+		debug2_f("checking CA key");
+		if ((r = is_key_revoked(krl, key->cert->signature_key)) != 0)
+			return r;
+	}
+	KRL_DBG(("key okay"));
+	return 0;
+}
+
+int
+ssh_krl_file_contains_key(const char *path, const struct sshkey *key)
+{
+	struct sshbuf *krlbuf = NULL;
+	struct ssh_krl *krl = NULL;
+	int oerrno = 0, r;
+
+	if (path == NULL)
+		return 0;
+	if ((r = sshbuf_load_file(path, &krlbuf)) != 0) {
+		oerrno = errno;
+		goto out;
+	}
+	if ((r = ssh_krl_from_blob(krlbuf, &krl)) != 0)
+		goto out;
+	debug2_f("checking KRL %s", path);
+	r = ssh_krl_check_key(krl, key);
+ out:
+	sshbuf_free(krlbuf);
+	ssh_krl_free(krl);
+	if (r != 0)
+		errno = oerrno;
+	return r;
+}
+
+int
+krl_dump(struct ssh_krl *krl, FILE *f)
+{
+	struct sshkey *key = NULL;
+	struct revoked_blob *rb;
+	struct revoked_certs *rc;
+	struct revoked_serial *rs;
+	struct revoked_key_id *rki;
+	int r, ret = 0;
+	char *fp, timestamp[64];
+
+	/* Try to print in a KRL spec-compatible format */
+	format_timestamp(krl->generated_date, timestamp, sizeof(timestamp));
+	fprintf(f, "# KRL version %llu\n",
+	    (unsigned long long)krl->krl_version);
+	fprintf(f, "# Generated at %s\n", timestamp);
+	if (krl->comment != NULL && *krl->comment != '\0') {
+		r = INT_MAX;
+		asmprintf(&fp, INT_MAX, &r, "%s", krl->comment);
+		fprintf(f, "# Comment: %s\n", fp);
+		free(fp);
+	}
+	fputc('\n', f);
+
+	RB_FOREACH(rb, revoked_blob_tree, &krl->revoked_keys) {
+		if ((r = sshkey_from_blob(rb->blob, rb->len, &key)) != 0) {
+			ret = SSH_ERR_INVALID_FORMAT;
+			error_r(r, "parse KRL key");
+			continue;
+		}
+		if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
+		    SSH_FP_DEFAULT)) == NULL) {
+			ret = SSH_ERR_INVALID_FORMAT;
+			error("sshkey_fingerprint failed");
+			continue;
+		}
+		fprintf(f, "hash: %s # %s\n", fp, sshkey_ssh_name(key));
+		free(fp);
+		free(key);
+	}
+	RB_FOREACH(rb, revoked_blob_tree, &krl->revoked_sha256s) {
+		fp = tohex(rb->blob, rb->len);
+		fprintf(f, "hash: SHA256:%s\n", fp);
+		free(fp);
+	}
+	RB_FOREACH(rb, revoked_blob_tree, &krl->revoked_sha1s) {
+		/*
+		 * There is not KRL spec keyword for raw SHA1 hashes, so
+		 * print them as comments.
+		 */
+		fp = tohex(rb->blob, rb->len);
+		fprintf(f, "# hash SHA1:%s\n", fp);
+		free(fp);
+	}
+
+	TAILQ_FOREACH(rc, &krl->revoked_certs, entry) {
+		fputc('\n', f);
+		if (rc->ca_key == NULL)
+			fprintf(f, "# Wildcard CA\n");
+		else {
+			if ((fp = sshkey_fingerprint(rc->ca_key,
+			    SSH_FP_HASH_DEFAULT, SSH_FP_DEFAULT)) == NULL) {
+				ret = SSH_ERR_INVALID_FORMAT;
+				error("sshkey_fingerprint failed");
+				continue;
+			}
+			fprintf(f, "# CA key %s %s\n",
+			    sshkey_ssh_name(rc->ca_key), fp);
+			free(fp);
+		}
+		RB_FOREACH(rs, revoked_serial_tree, &rc->revoked_serials) {
+			if (rs->lo == rs->hi) {
+				fprintf(f, "serial: %llu\n",
+				    (unsigned long long)rs->lo);
+			} else {
+				fprintf(f, "serial: %llu-%llu\n",
+				    (unsigned long long)rs->lo,
+				    (unsigned long long)rs->hi);
+			}
+		}
+		RB_FOREACH(rki, revoked_key_id_tree, &rc->revoked_key_ids) {
+			/*
+			 * We don't want key IDs with embedded newlines to
+			 * mess up the display.
+			 */
+			r = INT_MAX;
+			asmprintf(&fp, INT_MAX, &r, "%s", rki->key_id);
+			fprintf(f, "id: %s\n", fp);
+			free(fp);
+		}
+	}
+	return ret;
+}