X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/tripe/blobdiff_plain/b4e566689f469cc1cffe99e50e16a346d0f9832d..b5c45da15703d85b506a1ea1eb38c318c3418ed3:/keymgmt.c

diff --git a/keymgmt.c b/keymgmt.c
index 2935f1c9..e05706ac 100644
--- a/keymgmt.c
+++ b/keymgmt.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: keymgmt.c,v 1.5 2004/04/08 01:36:17 mdw Exp $
+ * $Id: keymgmt.c,v 1.6 2004/04/18 18:08:11 mdw Exp $
  *
  * Key loading and storing
  *
@@ -34,6 +34,7 @@
 
 group *gg;
 mp *kpriv;
+algswitch algs;
 
 /*----- Static variables --------------------------------------------------*/
 
@@ -159,6 +160,132 @@ static const kgops kgec_ops = { "tripe-ec", kgec_priv, kgec_pub };
 
 static const kgops *kgtab[] = { &kgdh_ops, &kgec_ops, 0 };
 
+/*----- Algswitch stuff ---------------------------------------------------*/
+
+/* --- @algs_get@ --- *
+ *
+ * Arguments:	@algswitch *a@ = where to put the algorithms
+ *		@key_file *kf@ = key file (for some stupid reason)
+ *		@key *k@ = key to inspect
+ *
+ * Returns:	Null if OK, or an error message.
+ *
+ * Use:		Extracts an algorithm choice from a key.
+ */
+
+static const char *algs_get(algswitch *a, key_file *kf, key *k)
+{
+  const char *p;
+  char *q;
+  dstr d = DSTR_INIT;
+  const char *e;
+
+#define FAIL(msg) do { e = msg; goto done; } while (0)
+
+  if ((p = key_getattr(kf, k, "cipher")) == 0)
+    p = "blowfish-cbc";
+  if ((a->c = gcipher_byname(p)) == 0)
+    FAIL("unknown cipher");
+
+  if ((p = key_getattr(kf, k, "hash")) == 0)
+    p = "rmd160";
+  if ((a->h = ghash_byname(p)) == 0)
+    FAIL("unknown hash function");
+
+  if ((p = key_getattr(kf, k, "mgf")) != 0) {
+    dstr_reset(&d);
+    dstr_putf(&d, "%s-mgf");
+    p = d.buf;
+  }
+  if ((a->mgf = gcipher_byname(p)) == 0)
+    FAIL("unknown MGF cipher");
+
+  if ((p = key_getattr(kf, k, "mac")) != 0) {
+    dstr_reset(&d);
+    dstr_puts(&d, p);
+    if ((q = strchr(d.buf, '/')) != 0)
+      *q++ = 0;
+    if ((a->m = gmac_byname(d.buf)) == 0)
+      FAIL("unknown message authentication code");
+    if (!q)
+      a->tagsz = a->m->hashsz;
+    else {
+      unsigned long n = strtoul(q, &q, 0);
+      if (*q) FAIL("bad tag length string");
+      if (n%8 || n > ~(size_t)0) FAIL("bad tag length");
+      a->tagsz = n/8;
+    }
+  } else {
+    dstr_reset(&d);
+    dstr_putf(&d, "%s-hmac", a->h->name);
+    if ((a->m = gmac_byname(d.buf)) == 0)
+      FAIL("failed to derive HMAC from hash function");
+    a->tagsz = a->h->hashsz/2;
+  }
+
+  e = 0;
+done:
+  dstr_destroy(&d);
+  return (e);
+}
+
+/* --- @algs_check@ --- *
+ *
+ * Arguments:	@algswitch *a@ = a choice of algorithms
+ *		@const group *g@ = the group we're working in
+ *
+ * Returns:	Null if OK, or an error message.
+ *
+ * Use:		Checks an algorithm choice for sensibleness.  This also
+ *		derives some useful information from the choices, and you
+ *		must call this before committing the algorithm selection
+ *		for use by @keyset@ functions.
+ */
+
+static const char *algs_check(algswitch *a, const group *g)
+{
+  /* --- Derive the key sizes --- *
+   *
+   * Must ensure that we have non-empty keys.  This isn't ideal, but it
+   * provides a handy sanity check.
+   */
+
+  a->hashsz = a->h->hashsz;
+  if ((a->cksz = keysz(a->hashsz, a->c->keysz)) == 0)
+    return ("no key size found for cipher");
+  if ((a->mksz = keysz(a->hashsz, a->m->keysz)) == 0)
+    return ("no key size found for MAC");
+
+  /* --- Ensure that the tag size is sane --- */
+
+  if (a->tagsz > a->m->hashsz) return ("tag length too large");
+
+  /* --- Ensure the MGF accepts hashes as keys --- */
+
+  if (keysz(a->hashsz, a->mgf->keysz) != a->hashsz)
+    return ("MGF not suitable -- restrictive key schedule");
+
+  /* --- All ship-shape and Bristol-fashion --- */
+
+  return (0);
+}
+
+/* --- @algs_samep@ --- *
+ *
+ * Arguments:	@const algswitch *a, *aa@ = two algorithm selections
+ *
+ * Returns:	Nonzero if the two selections are the same.
+ *
+ * Use:		Checks sameness of algorithm selections: used to ensure that
+ *		peers are using sensible algorithms.
+ */
+
+static int algs_samep(const algswitch *a, const algswitch *aa)
+{
+  return (a->c == aa->c && a->mgf == aa->mgf && a->h == aa->h &&
+	  a->m == aa->m && a->tagsz == aa->tagsz);
+}
+
 /*----- Main code ---------------------------------------------------------*/
 
 /* --- @keymoan@ --- *
@@ -196,6 +323,7 @@ static int loadpriv(dstr *d)
   int rc = -1;
   const kgops **ko;
   const char *e;
+  algswitch a;
 
   /* --- Open the private key file --- */
 
@@ -237,6 +365,15 @@ tymatch:;
     goto done_1;
   }
 
+  /* --- Collect the algorithms --- */
+
+  if ((e = algs_get(&a, &kf, k)) != 0 ||
+      (e = algs_check(&a, g)) != 0) {
+    dstr_putf(d, "bad symmetric algorithm selection in private key `%s': %s",
+	      t.buf, e);
+    goto done_1;
+  }
+
   /* --- Good, we're happy --- *
    *
    * Dodginess!  We change the group over here, but don't free any old group
@@ -263,12 +400,18 @@ tymatch:;
       trace(T_CRYPTO, "crypto: r = %s", mpstr(g->r));
       trace(T_CRYPTO, "crypto: h = %s", mpstr(g->h));
       trace(T_CRYPTO, "crypto: x = %s", mpstr(x));
+      trace(T_CRYPTO, "crypto: cipher = %s", a.c->name);
+      trace(T_CRYPTO, "crypto: mgf = %s", a.mgf->name);
+      trace(T_CRYPTO, "crypto: hash = %s", a.h->name);
+      trace(T_CRYPTO, "crypto: mac = %s/%lu",
+	    a.m->name, (unsigned long)a.tagsz * 8);
     })
   })
 
   /* --- Success! --- */
 
   gg = g; g = 0;
+  algs = a;
   kpriv = x; x = 0;
   rc = 0;
 
@@ -367,6 +510,7 @@ int km_interval(void)
 void km_init(const char *priv, const char *pub, const char *tag)
 {
   dstr d = DSTR_INIT;
+  const gchash *const *hh;
 
   kr_priv = priv;
   kr_pub = pub;
@@ -374,6 +518,13 @@ void km_init(const char *priv, const char *pub, const char *tag)
   fwatch_init(&w_priv, kr_priv);
   fwatch_init(&w_pub, kr_pub);
 
+  for (hh = ghashtab; *hh; hh++) {
+    if ((*hh)->hashsz > MAXHASHSZ) {
+      die(EXIT_FAILURE, "INTERNAL ERROR: %s hash length %lu > MAXHASHSZ %d",
+	  (*hh)->name, (unsigned long)(*hh)->hashsz, MAXHASHSZ);
+    }
+  }
+
   DRESET(&d);
   if (loadpriv(&d))
     die(EXIT_FAILURE, "%s", d.buf);
@@ -401,12 +552,13 @@ int km_getpubkey(const char *tag, ge *kpub, time_t *t_exp)
   const char *e;
   group *g = 0;
   ge *p = 0;
+  algswitch a;
   int rc = -1;
 
   /* --- Find the key --- */
 
   if (key_qtag(kf_pub, tag, &t, &k, &kd)) {
-    a_warn("private key `%s' not found in keyring `%s'", tag_priv, kr_priv);
+    a_warn("public key `%s' not found in keyring `%s'", tag, kr_pub);
     goto done;
   }
 
@@ -445,6 +597,17 @@ tymatch:;
     goto done;
   }
 
+  /* --- Check the algorithms --- */
+
+  if ((e = algs_get(&a, kf_pub, k)) != 0) {
+    a_warn("public key `%s' has bad algorithm selection: %s", t.buf, e);
+    goto done;
+  }
+  if (!algs_samep(&a, &algs)) {    
+    a_warn("public key `%s' specifies different algorithms", t.buf);
+    goto done;
+  }
+
   /* --- Dump the public key --- */
 
   IF_TRACING(T_KEYMGMT, {