diff --git a/Makefile b/Makefile
index 2cd3f04..09e943b 100644
--- a/Makefile
+++ b/Makefile
@@ -19,7 +19,7 @@
 	chmod a+x $@
 
 P =	cassh
-V =	2
+V =	0
 
 PREFIX =	/usr/local
 MANPREFIX =	${PREFIX}/man
diff --git a/cassh-keyfile.1 b/cassh-keyfile.1
index 570d2d2..bd1e777 100644
--- a/cassh-keyfile.1
+++ b/cassh-keyfile.1
@@ -11,7 +11,7 @@
 .\" along with this software. If not, see
 .\" <http://creativecommons.org/publicdomain/zero/1.0/>.
 .\"
-.Dd April 20, 2022
+.Dd April 07, 2022
 .Dt CASSH-KEYFILE 1
 .Os
 .Sh NAME
diff --git a/cassh-keyfile.sh b/cassh-keyfile.sh
index 5094b8e..4490a09 100644
--- a/cassh-keyfile.sh
+++ b/cassh-keyfile.sh
@@ -27,7 +27,7 @@ fi
 cassh_command=$2
 needs_agent=false
 case $cassh_command in
-issue|revoke)
+issue)
 	needs_agent=true
 	;;
 esac
diff --git a/cassh.1 b/cassh.1
index 24529ac..aa4400d 100644
--- a/cassh.1
+++ b/cassh.1
@@ -11,7 +11,7 @@
 .\" along with this software. If not, see
 .\" <http://creativecommons.org/publicdomain/zero/1.0/>.
 .\"
-.Dd April 20, 2022
+.Dd March 01, 2022
 .Dt CASSH 1
 .Os
 .Sh NAME
@@ -30,19 +30,13 @@
 .Bk -words
 .Cm mkfile
 .Ic authorized_keys
-.Op options ...
+.Op options
 .Ek
 .Nm
 .Bk -words
 .Cm mkfile
 .Ic known_hosts
-.Op hostnames ...
-.Ek
-.Nm
-.Bk -words
-.Cm revoke
-.Op Fl qv
-.Ar
+.Op hostnames
 .Ek
 .Sh DESCRIPTION
 .Nm
@@ -62,14 +56,9 @@ A Certification Authority directory consists of a
 .Pa ./ca.pub
 file corresponding to the public key of it, a
 .Pa ./pubkeys/
-directory which holds the public keys to be signed, an optional
-.Pa ./krl
-file corresponding to the last issued Key Revocation List, and optional
-.Pa ./ca_serial.txt
-and
-.Pa ./krl_serial.txt
-files corresponding to the current serial number for the issued certificates
-and Key Revocation Lists.
+directory which holds the public keys to be signed, and an optional
+.Pa ./serial.txt
+file holding the current serial number for the issued certificates.
 .Pp
 The following commands are available to
 .Nm :
@@ -95,15 +84,9 @@ The recognized tokens are:
 A literal
 .Sq % .
 .It \&%C
-The Certification Authority private key comment field as reported by
-.Xr ssh-add 1 ,
-or the string
-.Sq cassh
-if there is no comment reported.
+The Certification Authority private key comment.
 .It %f
-The basename of the public key being signed, without
-.Sq .pub
-suffix.
+The basename of the public key being signed.
 .El
 .Pp
 .Ar key_id
@@ -117,56 +100,37 @@ accepts the tokens %% and %f.
 After token expansion, all recognized options are passed down to
 .Xr ssh-keygen 1
 process.
-.It Cm mkfile Ic authorized_keys Op Ar options ...
+.It Cm mkfile Ic authorized_keys Op Ar options
 Write an
 .Ic authorized_keys
 file on standard output corresponding to the current Certification
 Authority.
 .Ar options
-are concatenated with commas and copied verbatim to the output.
+is copied verbatim to the output, and
 .Cm cert-authority
-is always added to the options list.
+is always added.
 See
 .Xr sshd 8 AUTHORIZED_KEYS FILE FORMAT
 for details.
-.It Cm mkfile Ic known_hosts Op Ar hostnames ...
+.It Cm mkfile Ic known_hosts Op Ar hostnames
 Write a
 .Ic known_hosts
 file on standard output corresponding to the current Certification
 Authority.
 .Ar hostnames
-are concatenated with commas and copied verbatim to the output.
+is copied verbatim to the output.
 See
 .Xr sshd 8 SSH_KNOWN_HOSTS FILE FORMAT
 for details.
-.It Cm revoke Oo Fl qv Oc Ar
-Generates a Key Revocation List for the current Certification Authority.
-All recognized options are passed down to
-.Xr ssh-keygen 1
-process.
-See
-.Xr ssh-keygen 1 KEY REVOCATION LISTS
-for details on the file format for input files.
-If
-.Pa ./krl
-exists,
-.Cm revoke
-will update.
-.Pa ./krl
-can be synced back with the input files by first removing it.
 .El
 .Sh FILES
-.Bl -tag -width MMMMMMMMMMMMMMMMMM -compact
+.Bl -tag -width MMMMMMMMMMMMMM -compact
 .It Pa ./ca.pub
 Certification Authority public key
 .It Pa ./pubkeys/
 Directory containing the public keys to be signed
-.It Pa ./krl
-Key Revocation List
-.It Pa ./ca_serial.txt
-Last issued serial for certificates
-.It Pa ./krl_serial.txt
-Last issued serial for KRLs
+.It Pa ./serial.txt
+Last issued serial
 .El
 .Sh EXIT STATUS
 .Ex -std
diff --git a/cassh.pl b/cassh.pl
new file mode 100644
index 0000000..e5b558e
--- /dev/null
+++ b/cassh.pl
@@ -0,0 +1,299 @@
+#!/usr/bin/env perl
+# cassh - Manager for an OpenSSH Certification Authority
+#
+# Written in 2022 by Lucas
+#
+# To the extent possible under law, the author(s) have dedicated all
+# copyright and related and neighboring rights to this software to the
+# public domain worldwide. This software is distributed without any
+# warranty.
+# You should have received a copy of the CC0 Public Domain Dedication
+# along with this software. If not, see
+# <http://creativecommons.org/publicdomain/zero/1.0/>.
+
+use v5.14;
+use strict;
+use warnings;
+
+package SerialFile v1.0.0;
+
+use overload '0+' => \&value;
+
+sub new ($$)
+{
+	my $class = shift;
+	my $self = {};
+	bless $self, $class;
+	return $self->_init(@_);
+}
+
+sub _init ($$)
+{
+	my ($self, $file) = @_;
+
+	my $mode = -f $file ? "+<" : ">";
+	open(my $fh, $mode, $file) or die "can't open $file: $!";
+	my @lines = <$fh>;
+
+	my $counter;
+	if (@lines == 0) {
+		$counter = 0;
+	} elsif (@lines == 1 && $lines[0] =~ /^(\d+)$/) {
+		$counter = $1;
+	} else {
+		return undef;
+	}
+
+	$self->{_fh} = $fh;
+	$self->{_counter} = $counter;
+
+	return $self;
+}
+
+sub inc ($;$)
+{
+	use integer;
+	my ($self, $inc) = @_;
+	$self->{_counter} += $inc // 1;
+	return $self;
+}
+
+sub value ($)
+{
+	my $self = shift;
+	return $self->{_counter};
+}
+
+sub commit ($)
+{
+	my $self = shift;
+
+	truncate($self->{_fh}, 0) or return 0;
+	seek($self->{_fh}, 0, 0) or return 0;
+
+	return say {$self->{_fh}} $self->value();
+}
+
+sub DESTROY ($)
+{
+	local ($., $@, $!, $^E, $?);
+	my $self = shift;
+	close($self->{_fh});
+}
+
+package FormatToken v1.0.0;
+
+use List::Util qw(all);
+
+sub new ($)
+{
+	return bless {_tokens => {"%" => "%"}}, shift;
+}
+
+sub register ($;%)
+{
+	my ($self, %pairs) = @_;
+	for (keys %pairs) {
+		die "can't register $_" if !/^[A-Za-z]$/;
+		$self->{_tokens}->{$_} = $pairs{$_};
+	}
+	return $self;
+}
+
+sub deregister ($;%)
+{
+	my ($self, %pairs) = @_;
+	delete $self->{_tokens}->{$_} for (keys %pairs);
+	return $self;
+}
+
+sub format ($$)
+{
+	my ($self, $in) = @_;
+	die "can't format \"$in\"" unless
+	    all {defined $self->{_tokens}->{$_}} ($in =~ /%([A-Za-z%])/g);
+	return $in =~ s/%([A-Za-z%])/$self->{_tokens}->{$1}/egr;
+}
+
+package main;
+
+use Getopt::Long qw(:config posix_default bundling no_ignore_case);
+
+my $PATH_CA_PUB      = "./ca.pub";
+my $PATH_CA_SERIAL   = "./serial.txt";
+my $PATH_PUBKEYS_DIR = "./pubkeys";
+
+my %COMMANDS = (
+	issue  => \&main_issue,
+	mkfile => \&main_mkfile,
+);
+
+my $PROGNAME = ($0 =~ s,.*/,,r);
+
+sub usage ()
+{
+	print STDERR <<EOF;
+Usage:
+	$PROGNAME issue [-hqv] [-I key_id] [-n principals]
+	    [-V validity_interval]
+	$PROGNAME mkfile authorized_keys [options ...]
+	$PROGNAME mkfile known_hosts [hostnames ...]
+EOF
+	exit 1;
+}
+
+sub err (@)
+{
+	say STDERR "$PROGNAME: @_";
+	exit 1;
+}
+
+sub slurp ($)
+{
+	my $f = shift;
+
+	open(my $fh, "<", $f) or err "can't open $f";
+	local $/;
+	my $s = <$fh>;
+	close($fh);
+
+	return $s;
+}
+
+# Returns comment from the ssh-agent if any is returned, otherwise it
+# returns the public key's fingerprint.
+sub get_ca_sk_comment_from_pk ($)
+{
+	my $f = shift;
+
+	my ($fh, @ssh_keygen_lines, @ssh_add_lines);
+
+	open($fh, "-|", "ssh-keygen", "-l", "-f", $f) or err "can't fork: $!";
+	@ssh_keygen_lines = <$fh>;
+	close($fh);
+
+	open($fh, "-|", "ssh-add", "-l") or err "can't fork: $!";
+	@ssh_add_lines = <$fh>;
+	close($fh);
+
+	my $comment;
+	OUTER: foreach my $ssh_keygen_line (@ssh_keygen_lines) {
+		chomp($ssh_keygen_line);
+		my @ssh_keygen_parts = split(/ /, $ssh_keygen_line, 3);
+		foreach my $ssh_add_line (@ssh_add_lines) {
+			chomp($ssh_add_line);
+			my @ssh_add_parts = split(/ /, $ssh_add_line, 3);
+			if ($ssh_keygen_parts[1] eq $ssh_add_parts[1]) {
+				my $s = $ssh_add_parts[2];
+				$comment = substr($s, 0, rindex($s, " "));
+				last OUTER;
+			}
+		}
+	}
+
+	return $comment;
+}
+
+sub get_pubkeys_files ($)
+{
+	my $d = shift;
+
+	opendir(my $dh, "$d") or err "can't open directory $d";
+	my @files = map {"$d/$_"}
+	    grep {-f "$d/$_" && /\.pub$/ && !/-cert\.pub/} readdir($dh);
+	closedir($dh);
+
+	return @files;
+}
+
+
+sub main_issue ()
+{
+	my ($host, $key_id_fmt, $principals_fmt, $quiet, $verbose,
+	    $validity_interval);
+
+	$validity_interval = "always:forever";
+	$key_id_fmt = "%C/%f";
+	$verbose = 0;
+	GetOptions(
+		"h"   => \$host,
+		"I=s" => \$key_id_fmt,
+		"n=s" => \$principals_fmt,
+		"q"   => \$quiet,
+		"v+"  => \$verbose,
+		"V=s" => \$validity_interval,
+	) or usage;
+
+	usage if @ARGV != 0;
+
+	my ($hflag, $qflag, $vflag);
+	$hflag = "-h" if defined($host);
+	$qflag = "-q" if defined($quiet);
+	$vflag = "-" . ("v" x $verbose) if $verbose > 0;
+
+	my @files = get_pubkeys_files($PATH_PUBKEYS_DIR);
+	exit 0 if @files == 0;
+
+	my $formatter = FormatToken->new();
+	my $ca_sk_comment = get_ca_sk_comment_from_pk($PATH_CA_PUB) // "cassh";
+	$formatter->register(C => $ca_sk_comment);
+
+	my $serial = SerialFile->new($PATH_CA_SERIAL);
+
+	# Doing individual calls to ssh-keygen allows for using the filename as
+	# a token in principals and key_id format.
+	foreach my $file (@files) {
+		$formatter->register(f => $file =~ s,.*/(.*)\.pub$,$1,r);
+
+		my ($key_id, $principals);
+		$key_id = $formatter->format($key_id_fmt);
+		$principals = $formatter->format($principals_fmt) if
+		    defined($principals_fmt);
+
+		my @cmdopts = ("-I", $key_id, "-U", "-s", $PATH_CA_PUB,
+		    "-V", $validity_interval, "-z", $serial);
+		push(@cmdopts, "-h") if defined($host);
+		push(@cmdopts, $qflag) if defined($qflag);
+		push(@cmdopts, $vflag) if defined($vflag);
+		push(@cmdopts, "-n", $principals) if defined($principals);
+
+		system("ssh-keygen", @cmdopts, $file);
+		if ($? == -1) {
+			err "ssh-keygen: $!";
+		} elsif ($? != 0) {
+			exit $? >> 8;
+		}
+
+		$serial->inc()->commit() or err "can't save serial";
+	}
+}
+
+sub main_mkfile ()
+{
+	usage if @ARGV < 1;
+	my $file = shift @ARGV;
+
+	err "no $PATH_CA_PUB found" if ! -f $PATH_CA_PUB;
+
+	if ($file eq "authorized_keys") {
+		print join(" ", join(",", "cert-authority", @ARGV),
+		    slurp($PATH_CA_PUB));
+	} elsif ($file eq "known_hosts") {
+		print join(" ", grep {$_ ne ""} ('@cert-authority',
+		    join(",", @ARGV), slurp($PATH_CA_PUB)));
+	} else {
+		err "unknown file $file";
+	}
+}
+
+sub main ()
+{
+	usage if @ARGV < 1;
+
+	my $cmd = shift @ARGV;
+
+	usage if !defined($COMMANDS{$cmd});
+	$COMMANDS{$cmd}->();
+}
+
+main();
diff --git a/cassh.sh b/cassh.sh
index c1456c8..209b2b7 100644
--- a/cassh.sh
+++ b/cassh.sh
@@ -17,9 +17,8 @@ usage()
 Usage:
 	${0##*/} issue [-hqv] [-I key_id] [-n principals]
 	    [-V validity_interval]
-	${0##*/} mkfile authorized_keys [options ...]
-	${0##*/} mkfile known_hosts [hostnames ...]
-	${0##*/} revoke [-qv] file ...
+	${0##*/} mkfile authorized_keys [options]
+	${0##*/} mkfile known_hosts [hostnames]
 EOF
 	exit 1
 }
@@ -30,11 +29,29 @@ err()
 	exit 1
 }
 
-# Returns the comment from the loaded secret key in ssh-agent, if any is
-# present.
-get_ca_sk_comment_from_pk()
+strip_leading_zeros()
 {
-	ssh-keygen -lf "$1" 2>/dev/null | {
+	_s=$1
+	if [ -z "$_s" ]; then
+		return
+	fi
+	while [ X"${_s#0}" != X"$_s" ]; do
+		_s=${_s#0}
+	done
+	echo "${_s:-0}"
+}
+
+strcmp()
+{
+	_r=$(expr "X$1" "$2" "X$3")
+	[ "${_r:-0}" -eq 1 ]
+}
+
+# Returns comment from the ssh-agent if any is returned, otherwise it
+# returns the public key's fingerprint.
+get_ca_comment_from_sk()
+{
+	ssh-keygen -lf "$1" | {
 		read -r pk_sz pk_fp pk_extra
 		_comment=$(ssh-add -l | while read -r sk_sz sk_fp sk_extra; do
 			if [ "X$sk_fp" = "X$pk_fp" ]; then
@@ -42,67 +59,57 @@ get_ca_sk_comment_from_pk()
 				break
 			fi
 		done)
-		echo "${_comment:-}"
+		echo "${_comment:-${pk_fp#*:}}"
 	}
 }
 
-format()
+_template_fmt()
 {
-	_s=$1
-	shift
+	_allowed_chars=$1
+	_char=$2
+	if [ "X$_char" = X% ]; then
+		echo %
+		return $?
+	fi
 
-	_cleanup=unset
-	while [ $# -ge 2 ]; do
-		_k=$1 _v=$2
-		shift 2
-		case $_k in
-		[A-Za-z])
-			;;
-		*)
-			return 1
-			;;
-		esac
-		eval "_token_${_k}=\$_v"
-		_cleanup=$_cleanup" _token_${_k}"
-	done
-	if [ $# -ne 0 ]; then
+	case $_char in
+	[$_allowed_chars])
+		;;
+	*)
+		return 1
+		;;
+	esac
+
+	_v=$(eval echo '${_template_fmt_'"$_char"':-}')
+	if [ -z "$_v" ]; then
 		return 1
 	fi
 
+	echo "$_v"
+}
+
+template()
+{
+	_allowed=$1
+	_s=$2
 	_out=
+
 	while [ "${_s#*%}" != "$_s" ]; do
 		_t=${_s#*%}
 		_out=$_out${_s%"%"$_t}
 		_s=$_t
 		_c=${_s%${_s#?}}
 
-		if [ -z "${_c:-}" ]; then
+		_t=$(_template_fmt "$_allowed" "$_c")
+		if [ $? -ne 0 ]; then
 			return 1
-		elif [ X"${_c}" = X% ]; then
-			_out=$_out%
-		else
-			eval "_out=$_out\$_token_${_c}" || return 1
 		fi
+		_out=$_out$_t
 
 		_s=${_s#$_c}
 	done
 	_out=$_out$_s
 
-	eval "$_cleanup"
-
-	echo "$_out"
-}
-
-strjoin()
-{
-	_c=$1
-	shift
-
-	_out=
-	for _s; do
-		_out=${_out:+$_out$_c}$_s
-	done
-
 	echo "$_out"
 }
 
@@ -131,42 +138,64 @@ main_issue()
 		usage
 	fi
 
+	if [ ! -f "$PATH_CA_PUB" ]; then
+		err "no $PATH_CA_PUB found"
+	fi
+	if ! ssh-add $qflag $vflag -T "$PATH_CA_PUB"; then
+		err "can't use CA key"
+	fi
+	if [ ! -d "$PATH_PUBKEYS_DIR/" ]; then
+		err "no pubkeys directory found"
+	fi
+
 	if [ ! -f "$PATH_CA_SERIAL" ]; then
-		echo 1 >"$PATH_CA_SERIAL"
+		date -u +%Y%m%d000000000 >"$PATH_CA_SERIAL"
 	fi
 	read -r serial <"$PATH_CA_SERIAL"
-
-	if [ ! -d "$PATH_PUBKEYS_DIR" ]; then
-		exit 0
+	# Remove NNNNNNNNN suffix
+	serial_date=${serial%?????????}
+	current_date=$(date -u +%Y%m%d)
+	if strcmp "$current_date" ">" "$serial_date"; then
+		serial_date=$current_date
+		serial_counter=0
+	else
+		# Remove YYYYmmdd prefix and leading 
+		serial_counter=$(strip_leading_zeros "${serial#????????}")
 	fi
-	find "$PATH_PUBKEYS_DIR" -type f -name '*.pub' ! -name '*-cert.pub' |
-	    sort | {
-		ca_comment=$(get_ca_sk_comment_from_pk "$PATH_CA_PUB")
-		: ${ca_comment:=cassh}
+	serial=$(printf "%s%09u\n" "$serial_date" "$serial_counter")
 
+	_template_fmt_C=$(get_ca_comment_from_sk "$PATH_CA_PUB")
+	find "$PATH_PUBKEYS_DIR/" -type f -name '*.pub' ! -name '*-cert.pub' | {
+		rc=0
 		while read -r pk; do
 			pkname=${pk%.pub}
 			pkname=${pkname#$PATH_PUBKEYS_DIR/}
+			_template_fmt_f=$pkname
 
-			id=$(format "$key_id_fmt" C "$ca_comment" f "$pkname")
+			id=$(template Cf "$key_id_fmt")
 			set -- -I "$id" -Us "$PATH_CA_PUB" \
 			    $hflag $qflag $vflag \
 			    -V "$validity_interval" -z "$serial"
 
 			if $nflag; then
-				principals=$(format "$principals_fmt" \
-				    f "$pkname")
+				principals=$(template f "$principals_fmt")
 				ssh-keygen "$@" -n "$principals" "$pk"
 			else
 				ssh-keygen "$@" "$pk"
-			fi
-			if [ $? -ne 0 ]; then
-				exit 1
-			fi
+			fi || rc=1
 
-			serial=$(($serial + 1))
-			echo $serial >"$PATH_CA_SERIAL"
+			serial_counter=$(($serial_counter + 1))
+			if [ $serial_counter -ge 1000000000 ]; then
+				err "can't issue more certificates today"
+			fi
+			serial=$(printf "%s%09u\n" "$serial_date" \
+			    "$serial_counter" | tee "$PATH_CA_SERIAL")
+
+			if [ $rc -ne 0 ]; then
+				break
+			fi
 		done
+		return $rc
 	}
 }
 
@@ -190,11 +219,19 @@ main_mkfile()
 
 	case $file in
 	authorized_keys)
-		printf "%s " "$(strjoin , cert-authority "$@")"
+		if [ $# -gt 1 ]; then
+			usage
+		fi
+		options=cert-authority${1:+,$1}
+		printf "%s " "$options"
 		;;
 	known_hosts)
-		if [ $# -gt 0 ]; then
-			printf "@cert-authority %s " "$(strjoin , "$@")"
+		if [ $# -gt 1 ]; then
+			usage
+		fi
+		hostnames=${1:-}
+		if [ -n "$hostnames" ]; then
+			printf "@cert-authority %s " "$hostnames"
 		else
 			printf "@cert-authority "
 		fi
@@ -207,42 +244,10 @@ main_mkfile()
 	cat "$PATH_CA_PUB"
 }
 
-main_revoke()
-{
-	qflag=
-	vflag=
-	while getopts fqv flag; do
-		case $flag in
-		q)	qflag=-q ;;
-		v)	vflag=${vflag:--}v ;;
-		*)	usage ;;
-		esac
-	done
-	shift $(($OPTIND - 1))
-
-	if [ ! -f "$PATH_KRL_SERIAL" ]; then
-		echo 1 >"$PATH_KRL_SERIAL"
-	fi
-	read -r serial <"$PATH_KRL_SERIAL"
-
-	uflag=
-	if [ -f "$PATH_KRL" ]; then
-		uflag=-u
-	fi
-
-	ssh-keygen -kf "$PATH_KRL" -Us "$PATH_CA_PUB" -z "$serial" \
-	    $qflag $vflag $uflag "$@" || exit 1
-
-	serial=$(($serial + 1))
-	echo $serial >"$PATH_KRL_SERIAL"
-}
-
 set -u
 
 PATH_CA_PUB=./ca.pub
-PATH_CA_SERIAL=./ca_serial.txt
-PATH_KRL=./krl
-PATH_KRL_SERIAL=./krl_serial.txt
+PATH_CA_SERIAL=./serial.txt
 PATH_PUBKEYS_DIR=./pubkeys
 
 if [ $# -lt 1 ]; then
@@ -254,6 +259,5 @@ shift
 case $cmd in
 issue)	main_issue "$@" ;;
 mkfile)	main_mkfile "$@" ;;
-revoke)	main_revoke "$@" ;;
 *)	usage ;;
 esac