mod_proxy_beacon: accept a random hex: key for ProxyBeaconSecret

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1939364 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/mod/mod_proxy_beacon.xml

@@ -107,7 +107,7 @@ to the reverse proxy over unicast UDP datagrams</description>
     <highlight language="config">
 # Receive backend announcements on the cluster network interface (UDP).
 ProxyBeaconListen 0.0.0.0:5555
-ProxyBeaconSecret    "a-long-random-shared-cluster-secret"
+ProxyBeaconSecret    "hex:00112233445566778899aabbccddeeff"
 ProxyBeaconBalancer  cluster
 
 # A backend is dropped from rotation if it does not announce for 30 seconds.
@@ -126,7 +126,7 @@ ProxyPassReverse "/" "balancer://cluster/"
 # Announce this backend's routable origin to the proxy every 10 seconds (UDP).
 ProxyBeaconAddress   proxy.example.com:5555
 ProxyBeaconAdvertise http://10.0.0.5:8080
-ProxyBeaconSecret    "a-long-random-shared-cluster-secret"
+ProxyBeaconSecret    "hex:00112233445566778899aabbccddeeff"
 ProxyBeaconInterval  10
     </highlight>
 
@@ -446,7 +446,7 @@ is taken out of rotation</description>
 <directivesynopsis>
 <name>ProxyBeaconSecret</name>
 <description>Pre-shared secret used to authenticate announcements</description>
-<syntax>ProxyBeaconSecret <em>secret</em></syntax>
+<syntax>ProxyBeaconSecret <em>secret</em>|hex:<em>key</em></syntax>
 <contextlist><context>server config</context><context>virtual host</context>
 </contextlist>
 
@@ -474,11 +474,16 @@ is taken out of rotation</description>
     silently rejected (and logged), which appears as the backend never joining
     the balancer.</p>
 
-    <p>The secret must be at least 16 characters; shorter values are rejected
-    when the configuration is read. The MAC key is derived from it with a fast
-    hash and the authentication tag is 64 bits, so anyone who captures a single
-    announcement can test passphrase guesses offline at full speed: use a long
-    random value, not a memorable password.</p>
+    <p>Use a random key. Generate one with <code>openssl rand -hex 16</code>
+    and configure it as <code>hex:</code> followed by the 32 hex digits; that
+    value is used directly as the 128-bit MAC key, so there is nothing to guess.
+    Any other value is treated as a passphrase: it must be at least 16
+    characters, and the MAC key is derived from it with a fast hash. Because the
+    authentication tag is 64 bits, anyone who captures a single announcement can
+    test passphrase guesses offline at full speed, so a passphrase protects only
+    as well as it is random and long. A value that begins with <code>hex:</code>
+    is always read as a key and is rejected if it is not exactly 32 hex
+    digits.</p>
 
     <note type="warning"><title>The secret is a membership credential</title>
     <p>A valid MAC proves only that the sender holds the secret. It does not

modules/proxy/README.beacon

@@ -208,9 +208,10 @@ Authentication (ProxyBeaconSecret, REQUIRED):
   genuine sub-second announcements always advance. seq= is NOT used for replay
   (it resets when a backend restarts); the wall-clock ts= does not.
 
-  The secret must be at least 16 characters.  The key is MD5(passphrase) and the
-  tag is 64 bits: a captured announcement permits offline guessing at full speed,
-  so the secret should be long and random.  A valid MAC shows possession of the
+  "hex:<32 hex digits>" is the 128-bit SipHash key itself (openssl rand -hex 16):
+  no passphrase, nothing to guess.  Any other value is a passphrase of at least 16
+  characters; the key is then MD5(passphrase) and the tag is 64 bits, so a
+  captured announcement permits offline guessing at full speed.  A valid MAC shows possession of the
   secret, nothing more: every holder can register any reachable origin, speak for
   other members and consume slots/records.  The secret is a membership-
   administrator credential, not a boundary between partially trusted workloads.

modules/proxy/mod_proxy_beacon-guide.md

@@ -80,7 +80,7 @@ httpd -l   | grep mod_proxy_beacon     # static build
 ```apache
 # Receive backend announcements on the cluster-facing interface (UDP/5555).
 ProxyBeaconListen   0.0.0.0:5555
-ProxyBeaconSecret   "a-long-random-shared-cluster-secret"
+ProxyBeaconSecret   "hex:00112233445566778899aabbccddeeff"
 ProxyBeaconBalancer cluster
 
 # Drop a backend from rotation if it goes silent for 30s; re-add on next beacon.
@@ -101,7 +101,7 @@ ProxyPassReverse "/" "balancer://cluster/"
 # Announce this backend's routable origin to the proxy every 10s (UDP).
 ProxyBeaconAddress   proxy.example.com:5555
 ProxyBeaconAdvertise http://10.0.0.5:8080
-ProxyBeaconSecret    "a-long-random-shared-cluster-secret"
+ProxyBeaconSecret    "hex:00112233445566778899aabbccddeeff"
 ProxyBeaconInterval  10
 ```
 
@@ -125,7 +125,7 @@ as an enabled member of `balancer://cluster` on the proxy. Stop one, and after
 | `ProxyBeaconListen [addr][:port]` | — | **Marks this server as the receiver.** Binds a UDP socket. `addr`/`port` are optional and inherited from the server's own `Listen`/`ServerName` when omitted (see note below). |
 | `ProxyBeaconBalancer name` | — | Balancer that announced backends are added to. Bare name (`cluster`); a leading `balancer://` is stripped. Must already exist with spare `growth`. |
 | `ProxyBeaconTimeout interval` | `0` (no eviction) | Seconds of silence before a member is disabled. `0` = add-only, never auto-remove. Set to a small multiple of the backends' interval to get self-healing. |
-| `ProxyBeaconSecret secret` | — (**required**) | Shared cluster secret; **same value on proxy and all backends**, at least 16 characters (long and random). The server fails to start if a participating server omits it or it is too short. |
+| `ProxyBeaconSecret secret` | — (**required**) | Shared cluster secret; **same value on proxy and all backends**, either `hex:` + 32 hex digits (a random key: `openssl rand -hex 16`) or a passphrase of at least 16 characters (weaker: guessable offline from one captured packet). The server fails to start if a participating server omits it or it is invalid. |
 | `ProxyBeaconMaxSkew interval` | `30` | Anti-replay freshness window: reject announcements whose signed timestamp is more than this far from now (either direction). Sub-second values (`500ms`) are honoured. |
 
 **Inheriting the listen address:** because UDP and TCP are separate port spaces,

modules/proxy/mod_proxy_beacon.c

@@ -168,6 +168,8 @@ typedef struct {
 #define BEACON_MAC_HEXLEN  (APR_SIPHASH_DSIZE * 2)
 /* Shortest ProxyBeaconSecret accepted. */
 #define BEACON_MIN_SECRET_LEN   16
+/* A secret of this form is used directly as the MAC key (no passphrase). */
+#define BEACON_HEXKEY_PREFIX    "hex:"
 #define BEACON_MAXSKEW_DEFAULT  apr_time_from_sec(30)
 
 /* Max announcement datagram we accept.  Our messages are a few hundred bytes;
@@ -409,6 +411,11 @@ static const char *beacon_set_timeout(cmd_parms *cmd, void *dummy,
     return NULL;
 }
 
+static int beacon_hexval(char c)
+{
+    return apr_isdigit(c) ? c - '0' : apr_tolower(c) - 'a' + 10;
+}
+
 static const char *beacon_set_secret(cmd_parms *cmd, void *dummy, const char *arg)
 {
     beacon_ctx_t *ctx = ap_get_module_config(cmd->server->module_config,
@@ -420,6 +427,29 @@ static const char *beacon_set_secret(cmd_parms *cmd, void *dummy, const char *ar
     if (!*arg) {
         return "ProxyBeaconSecret: empty secret";
     }
+    /* hex:<32 hex digits> is the key itself: a random 128-bit key has no
+     * passphrase to guess, so it needs no key derivation. */
+    if (!strncmp(arg, BEACON_HEXKEY_PREFIX, sizeof(BEACON_HEXKEY_PREFIX) - 1)) {
+        const char *h = arg + sizeof(BEACON_HEXKEY_PREFIX) - 1;
+        int i;
+
+        if (strlen(h) != 2 * sizeof(ctx->mac_key)) {
+            return apr_psprintf(cmd->pool,
+                                "ProxyBeaconSecret: hex: needs exactly %d hex "
+                                "digits (e.g. from 'openssl rand -hex %d')",
+                                (int)(2 * sizeof(ctx->mac_key)),
+                                (int)sizeof(ctx->mac_key));
+        }
+        for (i = 0; i < (int)sizeof(ctx->mac_key); i++) {
+            if (!apr_isxdigit(h[2 * i]) || !apr_isxdigit(h[2 * i + 1])) {
+                return "ProxyBeaconSecret: hex: value has a non-hex digit";
+            }
+            ctx->mac_key[i] = (unsigned char)
+                ((beacon_hexval(h[2 * i]) << 4) | beacon_hexval(h[2 * i + 1]));
+        }
+        ctx->has_secret = 1;
+        return NULL;
+    }
     /* The MAC key is derived from the passphrase with a fast hash, so anyone who
      * captures one announcement can test guesses offline at full speed; only a
      * long random secret resists that. */