X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=dh.c;h=261209aafedcfaa7077143e43fa27b268a507d10;hb=564022994befb8f71b89ae015751b22c34ae3ee8;hp=5917d39e0dd6f7df0b47ed0b2794a3a3e60f8f8e;hpb=ff05a229397c75142725f45cad191ce4a00625ce;p=secnet.git

diff --git a/dh.c b/dh.c
index 5917d39..261209a 100644
--- a/dh.c
+++ b/dh.c
@@ -1,5 +1,35 @@
+/*
+ * dh.c
+ */
+/*
+ * This file is Free Software.  It was originally written for secnet.
+ *
+ * Copyright 1995-2003 Stephen Early
+ * Copyright 2002-2014 Ian Jackson
+ *
+ * You may redistribute secnet as a whole and/or modify it under the
+ * terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 3, or (at your option) any
+ * later version.
+ *
+ * You may redistribute this file and/or modify it under the terms of
+ * the GNU General Public License as published by the Free Software
+ * Foundation; either version 2, or (at your option) any later
+ * version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this software; if not, see
+ * https://www.gnu.org/licenses/gpl.html.
+ */
+
 #include <stdio.h>
 #include <gmp.h>
+#include <limits.h>
 
 #include "secnet.h"
 #include "util.h"
@@ -11,7 +41,7 @@ struct dh {
     MP_INT p,g; /* prime modulus and generator */
 };
 
-static string_t dh_makepublic(void *sst, uint8_t *secret, uint32_t secretlen)
+static string_t dh_makepublic(void *sst, uint8_t *secret, int32_t secretlen)
 {
     struct dh *st=sst;
     string_t r;
@@ -22,7 +52,7 @@ static string_t dh_makepublic(void *sst, uint8_t *secret, uint32_t secretlen)
 
     read_mpbin(&a, secret, secretlen);
 
-    mpz_powm(&b, &st->g, &a, &st->p);
+    mpz_powm_sec(&b, &st->g, &a, &st->p);
 
     r=write_mpstring(&b);
 
@@ -31,9 +61,22 @@ static string_t dh_makepublic(void *sst, uint8_t *secret, uint32_t secretlen)
     return r;
 }
 
-static void dh_makeshared(void *sst, uint8_t *secret, uint32_t secretlen,
-			  string_t rempublic, uint8_t *sharedsecret,
-			  uint32_t buflen)
+static void write_mpbin_anomalous(MP_INT *a, uint8_t *buffer,
+				  int32_t buflen)
+    /* If the BN is smaller than buflen, pads it *at the wrong end* */
+{
+    char *hb = write_mpstring(a);
+    int32_t len;
+    hex_decode(buffer, buflen, &len, hb, True);
+    if (len<buflen)
+	memset(buffer+len,0,buflen-len);
+    free(hb);
+}
+
+static dh_makeshared_fn dh_makeshared;
+static void dh_makeshared(void *sst, uint8_t *secret, int32_t secretlen,
+			  cstring_t rempublic, uint8_t *sharedsecret,
+			  int32_t buflen)
 {
     struct dh *st=sst;
     MP_INT a, b, c;
@@ -45,9 +88,9 @@ static void dh_makeshared(void *sst, uint8_t *secret, uint32_t secretlen,
     read_mpbin(&a, secret, secretlen);
     mpz_set_str(&b, rempublic, 16);
 
-    mpz_powm(&c, &b, &a, &st->p);
+    mpz_powm_sec(&c, &b, &a, &st->p);
 
-    write_mpbin(&c,sharedsecret,buflen);
+    write_mpbin_anomalous(&c,sharedsecret,buflen);
 
     mpz_clear(&a);
     mpz_clear(&b);
@@ -61,7 +104,7 @@ static list_t *dh_apply(closure_t *self, struct cloc loc, dict_t *context,
     string_t p,g;
     item_t *i;
 
-    st=safe_malloc(sizeof(*st),"dh_apply");
+    NEW(st);
     st->cl.description="dh";
     st->cl.type=CL_DH;
     st->cl.apply=NULL;
@@ -112,12 +155,24 @@ static list_t *dh_apply(closure_t *self, struct cloc loc, dict_t *context,
 	    cfgfatal(loc,"diffie-hellman","modulus must be a prime\n");
 	}
     }
-    st->ops.len=mpz_sizeinbase(&st->p,2)/8;
+
+    size_t sz=mpz_sizeinbase(&st->p,2)/8;
+    if (sz>INT_MAX) {
+	cfgfatal(loc,"diffie-hellman","modulus far too large\n");
+    }
+    if (mpz_cmp(&st->g,&st->p) >= 0) {
+	cfgfatal(loc,"diffie-hellman","generator must be less than modulus\n");
+    }
+
+    st->ops.len=sz;
+
+    st->ops.ceil_len=(mpz_sizeinbase(&st->p,2)+7)/8;
+    /* According to the docs, mpz_sizeinbase(,256) is allowed to return
+     * an answer which is 1 too large.  But mpz_sizeinbase(,2) isn't. */
 
     return new_closure(&st->cl);
 }
 
-init_module dh_module;
 void dh_module(dict_t *dict)
 {
     add_closure(dict,"diffie-hellman",dh_apply);