From bde4a001b3ad4b90a4dbf5d31b18e30e42230e69 Mon Sep 17 00:00:00 2001
From: Nicola Tuveri <nic.tuv@gmail.com>
Date: Fri, 6 Sep 2019 00:18:36 +0300
Subject: [PATCH] Uniform bn_bn2binpad() and bn_bn2lebinpad() implementations

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/9793)
---
 crypto/bn/bn_lib.c | 77 +++++++++++++++++++++++++++++++++++++++-------
 crypto/bn_int.h    |  3 ++
 2 files changed, 69 insertions(+), 11 deletions(-)

diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c
index 8d9d8b32de..d4419a382c 100644
--- a/crypto/bn/bn_lib.c
+++ b/crypto/bn/bn_lib.c
@@ -658,8 +658,11 @@ BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret)
     return (ret);
 }
 
+typedef enum {big, little} endianess_t;
+
 /* ignore negative */
-static int bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
+static
+int bn2binpad(const BIGNUM *a, unsigned char *to, int tolen, endianess_t endianess)
 {
     int n;
     size_t i, lasti, j, atop, mask;
@@ -691,10 +694,17 @@ static int bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
 
     lasti = atop - 1;
     atop = a->top * BN_BYTES;
-    for (i = 0, j = 0, to += tolen; j < (size_t)tolen; j++) {
+    if (endianess == big)
+        to += tolen; /* start from the end of the buffer */
+    for (i = 0, j = 0; j < (size_t)tolen; j++) {
+        unsigned char val;
         l = a->d[i / BN_BYTES];
         mask = 0 - ((j - atop) >> (8 * sizeof(i) - 1));
-        *--to = (unsigned char)(l >> (8 * (i % BN_BYTES)) & mask);
+        val = (unsigned char)(l >> (8 * (i % BN_BYTES)) & mask);
+        if (endianess == big)
+            *--to = val;
+        else
+            *to++ = val;
         i += (i - lasti) >> (8 * sizeof(i) - 1); /* stay on last limb */
     }
 
@@ -705,21 +715,66 @@ int bn_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
 {
     if (tolen < 0)
         return -1;
-    return bn2binpad(a, to, tolen);
+    return bn2binpad(a, to, tolen, big);
 }
 
 int BN_bn2bin(const BIGNUM *a, unsigned char *to)
 {
-    int n, i;
+    return bn2binpad(a, to, -1, big);
+}
+
+BIGNUM *bn_lebin2bn(const unsigned char *s, int len, BIGNUM *ret)
+{
+    unsigned int i, m;
+    unsigned int n;
     BN_ULONG l;
+    BIGNUM *bn = NULL;
 
-    bn_check_top(a);
-    n = i = BN_num_bytes(a);
-    while (i--) {
-        l = a->d[i / BN_BYTES];
-        *(to++) = (unsigned char)(l >> (8 * (i % BN_BYTES))) & 0xff;
+    if (ret == NULL)
+        ret = bn = BN_new();
+    if (ret == NULL)
+        return NULL;
+    bn_check_top(ret);
+    s += len;
+    /* Skip trailing zeroes. */
+    for ( ; len > 0 && s[-1] == 0; s--, len--)
+        continue;
+    n = len;
+    if (n == 0) {
+        ret->top = 0;
+        return ret;
+    }
+    i = ((n - 1) / BN_BYTES) + 1;
+    m = ((n - 1) % (BN_BYTES));
+    if (bn_wexpand(ret, (int)i) == NULL) {
+        BN_free(bn);
+        return NULL;
+    }
+    ret->top = i;
+    ret->neg = 0;
+    l = 0;
+    while (n--) {
+        s--;
+        l = (l << 8L) | *s;
+        if (m-- == 0) {
+            ret->d[--i] = l;
+            l = 0;
+            m = BN_BYTES - 1;
+        }
     }
-    return (n);
+    /*
+     * need to call this due to clear byte at top if avoiding having the top
+     * bit set (-ve number)
+     */
+    bn_correct_top(ret);
+    return ret;
+}
+
+int bn_bn2lebinpad(const BIGNUM *a, unsigned char *to, int tolen)
+{
+    if (tolen < 0)
+        return -1;
+    return bn2binpad(a, to, tolen, little);
 }
 
 int BN_ucmp(const BIGNUM *a, const BIGNUM *b)
diff --git a/crypto/bn_int.h b/crypto/bn_int.h
index a552cc20be..6791154818 100644
--- a/crypto/bn_int.h
+++ b/crypto/bn_int.h
@@ -19,3 +19,6 @@ int bn_mul_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
 int bn_sqr_fixed_top(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx);
 
 int bn_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen);
+
+BIGNUM *bn_lebin2bn(const unsigned char *s, int len, BIGNUM *ret);
+int bn_bn2lebinpad(const BIGNUM *a, unsigned char *to, int tolen);
-- 
2.25.1