X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?a=blobdiff_plain;f=dh.c;h=261209aafedcfaa7077143e43fa27b268a507d10;hb=49b56eafcd147185c28848a7c04e31a32c49a82e;hp=0616a43e4007dc330137431cbf8908b34823861c;hpb=e84c081039387230c524f9f34903afacaab4219b;p=secnet.git

diff --git a/dh.c b/dh.c
index 0616a43..261209a 100644
--- a/dh.c
+++ b/dh.c
@@ -61,6 +61,18 @@ static string_t dh_makepublic(void *sst, uint8_t *secret, int32_t secretlen)
     return r;
 }
 
+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,
@@ -78,7 +90,7 @@ static void dh_makeshared(void *sst, uint8_t *secret, int32_t secretlen,
 
     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);