From a43bb0fda6c7e288f2e7b13b2c37cafe5ee6de83 Mon Sep 17 00:00:00 2001
From: Karel Miko <miko@dcit.cz>
Date: Sun, 19 Jan 2014 23:13:20 +0100
Subject: [PATCH] dsa_encrypt_key small correction

---
 src/pk/dsa/dsa_encrypt_key.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/src/pk/dsa/dsa_encrypt_key.c b/src/pk/dsa/dsa_encrypt_key.c
index a082969..92be479 100644
--- a/src/pk/dsa/dsa_encrypt_key.c
+++ b/src/pk/dsa/dsa_encrypt_key.c
@@ -37,7 +37,7 @@ int dsa_encrypt_key(const unsigned char *in,   unsigned long inlen,
     unsigned char *expt, *skey;
     void          *g_pub, *g_priv;
     unsigned long  x, y;
-    int            err;
+    int            err, qbits;
 
     LTC_ARGCHK(in      != NULL);
     LTC_ARGCHK(out     != NULL);
@@ -75,18 +75,15 @@ int dsa_encrypt_key(const unsigned char *in,   unsigned long inlen,
        return CRYPT_MEM;
     }
     
-    /* make a random x, g^x pair */
-    x = mp_unsigned_bin_size(key->q);
-    if (prng_descriptor[wprng].read(expt, x, prng) != x) {
-       err = CRYPT_ERROR_READPRNG;
-       goto LBL_ERR;
-    }
-    
-    /* load x */
-    if ((err = mp_read_unsigned_bin(g_priv, expt, x)) != CRYPT_OK) {
-       goto LBL_ERR;
-    }
-    
+    /* make a random g_priv, g_pub = g^x pair */
+    qbits = mp_count_bits(key->q);
+    do {
+      if ((err = rand_bn_bits(g_priv, qbits, prng, wprng)) != CRYPT_OK) {
+        goto LBL_ERR;
+      }
+      /* private key x should be from range: 1 <= x <= q-1 (see FIPS 186-4 B.1.2) */
+    } while (mp_cmp_d(g_priv, 0) != LTC_MP_GT || mp_cmp(g_priv, key->q) != LTC_MP_LT);
+
     /* compute y */
     if ((err = mp_exptmod(key->g, g_priv, key->p, g_pub)) != CRYPT_OK) {
        goto LBL_ERR;