New BN functions.

Add new function BN_bn2binpad() which checks the length of the output
buffer and pads the result with zeroes if necessary.

New functions BN_bn2lebinpad() and BN_lebin2bn() which use little endian
format.
Reviewed-by: NRich Salz <rsalz@openssl.org>

crypto/bn/bn_lib.c

@@ -575,18 +575,104 @@ BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret)
 }
 
 /* ignore negative */
-int BN_bn2bin(const BIGNUM *a, unsigned char *to)
+static int bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
 {
-    int n, i;
+    int i;
     BN_ULONG l;
 
     bn_check_top(a);
-    n = i = BN_num_bytes(a);
+    i = BN_num_bytes(a);
+    if (tolen == -1)
+        tolen = i;
+    else if (tolen < i)
+        return -1;
+    /* Add leading zeroes if necessary */
+    if (tolen > i) {
+        memset(to, 0, tolen - i);
+        to += tolen - i;
+    }
     while (i--) {
         l = a->d[i / BN_BYTES];
         *(to++) = (unsigned char)(l >> (8 * (i % BN_BYTES))) & 0xff;
     }
-    return (n);
+    return tolen;
+}
+
+int BN_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen)
+{
+    if (tolen < 0)
+        return -1;
+    return bn2binpad(a, to, tolen);
+}
+
+int BN_bn2bin(const BIGNUM *a, unsigned char *to)
+{
+    return bn2binpad(a, to, -1);
+}
+
+BIGNUM *BN_lebin2bn(const unsigned char *s, int len, BIGNUM *ret)
+{
+    unsigned int i, m;
+    unsigned int n;
+    BN_ULONG l;
+    BIGNUM *bn = NULL;
+
+    if (ret == NULL)
+        ret = bn = BN_new();
+    if (ret == NULL)
+        return (NULL);
+    bn_check_top(ret);
+    s += len - 1;
+    /* Skip trailing zeroes. */
+    for ( ; len > 0 && *s == 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--) {
+        l = (l << 8L) | *(s--);
+        if (m-- == 0) {
+            ret->d[--i] = l;
+            l = 0;
+            m = BN_BYTES - 1;
+        }
+    }
+    /*
+     * 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)
+{
+    int i;
+    BN_ULONG l;
+    bn_check_top(a);
+    i = BN_num_bytes(a);
+    if (tolen < i)
+        return -1;
+    /* Add trailing zeroes if necessary */
+    if (tolen > i)
+        memset(to + i, 0, tolen - i);
+    to += i - 1;
+    while (i--) {
+        l = a->d[i / BN_BYTES];
+        *(to--) = (unsigned char)(l >> (8 * (i % BN_BYTES))) & 0xff;
+    }
+    return tolen;
 }
 
 int BN_ucmp(const BIGNUM *a, const BIGNUM *b)

crypto/pem/pvkfmt.c

@@ -93,23 +93,11 @@ static unsigned int read_ledword(const unsigned char **in)
 
 static int read_lebn(const unsigned char **in, unsigned int nbyte, BIGNUM **r)
 {
-    const unsigned char *p;
-    unsigned char *tmpbuf, *q;
-    unsigned int i;
-    p = *in + nbyte - 1;
-    tmpbuf = OPENSSL_malloc(nbyte);
-    if (tmpbuf == NULL)
-        return 0;
-    q = tmpbuf;
-    for (i = 0; i < nbyte; i++)
-        *q++ = *p--;
-    *r = BN_bin2bn(tmpbuf, nbyte, NULL);
-    OPENSSL_free(tmpbuf);
-    if (*r) {
-        *in += nbyte;
-        return 1;
-    } else
+    *r = BN_lebin2bn(*in, nbyte, NULL);
+    if (*r == NULL)
         return 0;
+    *in += nbyte;
+    return 1;
 }
 
 /* Convert private key blob to EVP_PKEY: RSA and DSA keys supported */
@@ -417,26 +405,8 @@ static void write_ledword(unsigned char **out, unsigned int dw)
 
 static void write_lebn(unsigned char **out, const BIGNUM *bn, int len)
 {
-    int nb, i;
-    unsigned char *p = *out, *q, c;
-    nb = BN_num_bytes(bn);
-    BN_bn2bin(bn, p);
-    q = p + nb - 1;
-    /* In place byte order reversal */
-    for (i = 0; i < nb / 2; i++) {
-        c = *p;
-        *p++ = *q;
-        *q-- = c;
-    }
-    *out += nb;
-    /* Pad with zeroes if we have to */
-    if (len > 0) {
-        len -= nb;
-        if (len > 0) {
-            memset(*out, 0, len);
-            *out += len;
-        }
-    }
+    BN_bn2lebinpad(bn, *out, len);
+    *out += len;
 }
 
 static int check_bitlen_rsa(RSA *rsa, int ispub, unsigned int *magic);

doc/crypto/BN_bn2bin.pod

@@ -2,16 +2,21 @@
 
 =head1 NAME
 
-BN_bn2bin, BN_bin2bn, BN_bn2hex, BN_bn2dec, BN_hex2bn, BN_dec2bn,
-BN_print, BN_print_fp, BN_bn2mpi, BN_mpi2bn - format conversions
+BN_bn2bin, BN_bin2bn, BN_bn2lebinpad, BN_lebin2bn, BN_bn2hex, BN_bn2dec,
+BN_hex2bn, BN_dec2bn, BN_print, BN_print_fp, BN_bn2mpi,
+BN_mpi2bn - format conversions
 
 =head1 SYNOPSIS
 
  #include <openssl/bn.h>
 
  int BN_bn2bin(const BIGNUM *a, unsigned char *to);
+ int BN_bn2binpad(const BIGNUM *a, unsigned char *to, int tolen);
  BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret);
 
+ int BN_bn2lebinpad(const BIGNUM *a, unsigned char *to, int tolen);
+ BIGNUM *BN_lebin2bn(const unsigned char *s, int len, BIGNUM *ret);
+
  char *BN_bn2hex(const BIGNUM *a);
  char *BN_bn2dec(const BIGNUM *a);
  int BN_hex2bn(BIGNUM **a, const char *str);
@@ -29,10 +34,18 @@ BN_bn2bin() converts the absolute value of B<a> into big-endian form
 and stores it at B<to>. B<to> must point to BN_num_bytes(B<a>) bytes of
 memory.
 
+BN_bn2binpad() also converts the absolute value of B<a> into big-endian form
+and stores it at B<to>. B<tolen> indicates the length of the output buffer
+B<to>. The result is padded with zeroes if necessary. If B<tolen> is less than
+BN_num_bytes(B<a>) an error is returned.
+
 BN_bin2bn() converts the positive integer in big-endian form of length
 B<len> at B<s> into a B<BIGNUM> and places it in B<ret>. If B<ret> is
 NULL, a new B<BIGNUM> is created.
 
+BN_bn2lebinpad() and BN_bin2lbn() are identical to BN_bn2binpad() and
+BN_bin2bn() except the buffer is in little-endian format.
+
 BN_bn2hex() and BN_bn2dec() return printable strings containing the
 hexadecimal and decimal encoding of B<a> respectively. For negative
 numbers, the string is prefaced with a leading '-'. The string must be
@@ -67,6 +80,9 @@ if B<ret> is NULL.
 BN_bn2bin() returns the length of the big-endian number placed at B<to>.
 BN_bin2bn() returns the B<BIGNUM>, NULL on error.
 
+BN_bn2binpad() returns the number of bytes written or -1 if the supplied
+buffer is too small.
+
 BN_bn2hex() and BN_bn2dec() return a null-terminated string, or NULL
 on error. BN_hex2bn() and BN_dec2bn() return the number's length in
 hexadecimal or decimal digits, and 0 on error.

include/openssl/bn.h

@@ -270,6 +270,9 @@ BIGNUM *BN_copy(BIGNUM *a, const BIGNUM *b);
 void BN_swap(BIGNUM *a, BIGNUM *b);
 BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret);
 int BN_bn2bin(const BIGNUM *a, unsigned char *to);
+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);
 BIGNUM *BN_mpi2bn(const unsigned char *s, int len, BIGNUM *ret);
 int BN_bn2mpi(const BIGNUM *a, unsigned char *to);
 int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);