From 9898b1877ce2973bbc336921969bd7f16d3698fa Mon Sep 17 00:00:00 2001
From: Guilhem Moulin <guilhem@fripost.org>
Date: Sun, 21 Feb 2021 18:49:14 +0100
Subject: lacme-accountd(1): new setting 'keyid'.

This saves a round trip and provides a safeguard against malicious
clients.
---
 client | 56 +++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 41 insertions(+), 15 deletions(-)

(limited to 'client')

diff --git a/client b/client
index 7a63259..d7874b7 100755
--- a/client
+++ b/client
@@ -90,7 +90,7 @@ do {
             print STDERR "WARN: Ignoring extra greeting data from accountd \"$extra\"\n";
         } else {
             print STDERR "Received extra greeting data from accountd: $extra\n" if $ENV{DEBUG};
-            ($JWK_thumbprint, $ALG) = @$h{qw/jwk-thumbprint alg/};
+            ($JWK_thumbprint, $ALG, $KID) = @$h{qw/jwk-thumbprint alg kid/};
         }
     }
     my $jwk_str = $S->getline() // die "ERROR: No JWK from lacme-accountd\n";
@@ -194,39 +194,50 @@ sub request_json_decode($;$$) {
 
 
 #############################################################################
-# JSON-encode the hash reference $h and send it to the ACME server $uri
-# encapsulated it in a JSON Web Signature (JWS).
+# JSON-encode the hash reference $payload and send it to the ACME server
+# $url encapsulated it in a JSON Web Signature (JWS).  $header MUST
+# contain either "jwk" (JSON Web Key) or "kid" per RFC 8555 sec. 6.2
 # https://tools.ietf.org/html/rfc8555
 #
-sub acme($;$) {
-    my ($uri, $h) = @_;
-    die "Missing nonce\n" unless defined $NONCE;
+sub acme2($$;$) {
+    my ($url, $header, $payload) = @_;
 
     # Produce the JSON Web Signature: RFC 7515 section 5
-    my %header = ( alg => $ALG, nonce => $NONCE, url => $uri );
-    defined $KID ? ($header{kid} = $KID) : ($header{jwk} = $JWK);
-    my $payload = defined $h ? encode_base64url(json()->encode($h)) : "";
-    my $protected = encode_base64url(json()->encode(\%header));
-    my $data = $protected .'.'. $payload;
-    $S->printflush($data, "\r\n");
+    $header->{alg} = $ALG;
+    $header->{nonce} = $NONCE // die "Missing nonce\n";
+    $header->{url} = $url;
+    my $protected = encode_base64url(json()->encode($header));
+    $payload = defined $payload ? encode_base64url(json()->encode($payload)) : "";
+
+    $S->printflush($protected, ".", $payload, "\r\n");
     my $sig = $S->getline() // die "ERROR: No response from lacme-accountd\n";
     $sig =~ s/\r\n\z// or die;
     undef $NONCE; # consume the nonce
 
     # Flattened JSON Serialization, RFC 7515 section 7.2.2
-    request(POST => $uri, {
+    request(POST => $url, {
         payload => $payload,
         protected => $protected,
         signature => $sig
     });
 }
 
+# Like above, but always use "kid"
+sub acme($;$) {
+    my ($url, $payload) = @_;
+    die "Missing KID\n" unless defined $KID;
+    acme2($url, {kid => $KID}, $payload)
+}
+
 my $SERVER_URI = $CONFIG->{server} // '@@acmeapi_server@@';
 
 my %RES;
 # Get the resource URI from the directory
 sub acme_resource($%) {
     my $r = shift;
+    my %payload = @_;
+    my %protected;
+
     unless (%RES) {
         # query the ACME directory to get resources URIs
         %RES = %{ request_json_decode(request(GET => $SERVER_URI)) };
@@ -235,12 +246,23 @@ sub acme_resource($%) {
         request(HEAD => $RES{newNonce});
     }
     my $uri = $RES{$r} // die "Unknown resource '$r'\n";
-    acme($uri, {@_});
+
+    if ($r eq "newAccount" or ($r eq "revokeCert" and !defined $KID)) {
+        # per RFC 8555 sec. 6.2 these requests MUST have a JWK
+        print STDERR "WARNING: lacme-accountd supplied an empty JWK; try removing 'keyid' ",
+                     "setting from lacme-accountd.conf if the ACME resource request fails.\n"
+            unless %$JWK;
+        return acme2($uri, {jwk => $JWK}, \%payload);
+    } else {
+        # per RFC 8555 sec. 6.2 all other requests MUST have a KID
+        return acme($uri, \%payload);
+    }
 }
 
 # Set the key ID (registration URI)
 sub set_kid(;$) {
     my $die = shift // 1;
+    return if defined $KID; # already set
     my $r = acme_resource('newAccount', onlyReturnExisting => JSON::true );
     if ($r->is_success()) {
         $KID = $r->header('Location');
@@ -269,6 +291,7 @@ if ($COMMAND eq 'account') {
 
     if ($r->is_success()) {
         $KID = $r->header('Location');
+        print STDERR "Key ID: $KID\n";
         $r = acme($KID, \%h);
         request_json_decode($r, 1, \*STDOUT)
             if $r->is_success() and $r->content_type() eq 'application/json';
@@ -391,7 +414,10 @@ elsif ($COMMAND eq 'revokeCert') {
     my $der = do { local $/ = undef; <STDIN> };
     close STDIN or die "close: $!";
 
-    # send a KID if the request is signed with the acccount key, otherwise send a JWK
+    # RFC 8555 sec. 6.2: send a KID if the request is signed with the
+    # acccount key, otherwise send a JWK
+    # We have no way to know which of the account key or certificate key
+    # is used, so we try to get a KID and fallback to sending the JWK
     set_kid(0);
 
     my $r = acme_resource('revokeCert', certificate => encode_base64url($der));
-- 
cgit v1.2.3