Patch comes from upstream:

  http://git.openssl.org/gitweb/?p=openssl.git;a=commit;h=2198be3483259de374f91e57d247d0fc667aef29

It will be obsoleted when openssl-1.0.0m is available.

--- openssl-1.0.0l/crypto/bn/bn.h.orig	Mon Jan  6 07:00:59 2014

+++ openssl-1.0.0l/crypto/bn/bn.h		Fri Apr 18 13:03:57 2014

@@ -538,6 +538,8 @@

 BIGNUM *BN_mod_sqrt(BIGNUM *ret,

 	const BIGNUM *a, const BIGNUM *n,BN_CTX *ctx);

+void	BN_consttime_swap(BN_ULONG swap, BIGNUM *a, BIGNUM *b, int nwords);

+

 /* Deprecated versions */

 #ifndef OPENSSL_NO_DEPRECATED

 BIGNUM *BN_generate_prime(BIGNUM *ret,int bits,int safe,

@@ -759,11 +761,20 @@

 #define bn_fix_top(a)		bn_check_top(a)

+#define bn_check_size(bn, bits) bn_wcheck_size(bn, ((bits+BN_BITS2-1))/BN_BITS2)

+#define bn_wcheck_size(bn, words) \

+	do { \

+		const BIGNUM *_bnum2 = (bn); \

+		assert(words <= (_bnum2)->dmax && words >= (_bnum2)->top); \

+	} while(0)

+

 #else /* !BN_DEBUG */

 #define bn_pollute(a)

 #define bn_check_top(a)

 #define bn_fix_top(a)		bn_correct_top(a)

+#define bn_check_size(bn, bits)

+#define bn_wcheck_size(bn, words)

 #endif

--- openssl-1.0.0l/crypto/bn/bn_lib.c.orig	Mon Jan  6 07:00:59 2014

+++ openssl-1.0.0l/crypto/bn/bn_lib.c		Fri Apr 18 13:03:08 2014

@@ -843,3 +843,55 @@

 		}

 	return bn_cmp_words(a,b,cl);

 	}

+

+/* 

+ * Constant-time conditional swap of a and b.  

+ * a and b are swapped if condition is not 0.  The code assumes that at most one bit of condition is set.

+ * nwords is the number of words to swap.  The code assumes that at least nwords are allocated in both a and b,

+ * and that no more than nwords are used by either a or b.

+ * a and b cannot be the same number

+ */

+void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)

+	{

+	BN_ULONG t;

+	int i;

+

+	bn_wcheck_size(a, nwords);

+	bn_wcheck_size(b, nwords);

+

+	assert(a != b);

+	assert((condition & (condition - 1)) == 0);

+	assert(sizeof(BN_ULONG) >= sizeof(int));

+

+	condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;

+

+	t = (a->top^b->top) & condition;

+	a->top ^= t;

+	b->top ^= t;

+

+#define BN_CONSTTIME_SWAP(ind) \

+	do { \

+		t = (a->d[ind] ^ b->d[ind]) & condition; \

+		a->d[ind] ^= t; \

+		b->d[ind] ^= t; \

+	} while (0)

+

+

+	switch (nwords) {

+	default:

+		for (i = 10; i < nwords; i++) 

+			BN_CONSTTIME_SWAP(i);

+		/* Fallthrough */

+	case 10: BN_CONSTTIME_SWAP(9); /* Fallthrough */

+	case 9: BN_CONSTTIME_SWAP(8); /* Fallthrough */

+	case 8: BN_CONSTTIME_SWAP(7); /* Fallthrough */

+	case 7: BN_CONSTTIME_SWAP(6); /* Fallthrough */

+	case 6: BN_CONSTTIME_SWAP(5); /* Fallthrough */

+	case 5: BN_CONSTTIME_SWAP(4); /* Fallthrough */

+	case 4: BN_CONSTTIME_SWAP(3); /* Fallthrough */

+	case 3: BN_CONSTTIME_SWAP(2); /* Fallthrough */

+	case 2: BN_CONSTTIME_SWAP(1); /* Fallthrough */

+	case 1: BN_CONSTTIME_SWAP(0);

+	}

+#undef BN_CONSTTIME_SWAP

+}

--- openssl-1.0.0l/crypto/ec/ec2_mult.c.orig	Mon Jan  6 07:00:59 2014

+++ openssl-1.0.0l/crypto/ec/ec2_mult.c	Fri Apr 18 13:00:28 2014

@@ -206,11 +206,15 @@

 	return ret;

 	}

+

 /* Computes scalar*point and stores the result in r.

  * point can not equal r.

- * Uses algorithm 2P of

+ * Uses a modified algorithm 2P of

  *     Lopez, J. and Dahab, R.  "Fast multiplication on elliptic curves over 

  *     GF(2^m) without precomputation" (CHES '99, LNCS 1717).

+ *

+ * To protect against side-channel attack the function uses constant time swap,

+ * avoiding conditional branches.

  */

 static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,

 	const EC_POINT *point, BN_CTX *ctx)

@@ -244,6 +248,11 @@

 	x2 = &r->X;

 	z2 = &r->Y;

+	bn_wexpand(x1, group->field.top);

+	bn_wexpand(z1, group->field.top);

+	bn_wexpand(x2, group->field.top);

+	bn_wexpand(z2, group->field.top);

+

 	if (!BN_GF2m_mod_arr(x1, &point->X, group->poly)) goto err; /* x1 = x */

 	if (!BN_one(z1)) goto err; /* z1 = 1 */

 	if (!group->meth->field_sqr(group, z2, x1, ctx)) goto err; /* z2 = x1^2 = x^2 */

@@ -268,16 +277,12 @@

 		word = scalar->d[i];

 		while (mask)

 			{

-			if (word & mask)

-				{

-				if (!gf2m_Madd(group, &point->X, x1, z1, x2, z2, ctx)) goto err;

-				if (!gf2m_Mdouble(group, x2, z2, ctx)) goto err;

-				}

-			else

-				{

-				if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;

-				if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;

-				}

+			BN_consttime_swap(word & mask, x1, x2, group->field.top);

+			BN_consttime_swap(word & mask, z1, z2, group->field.top);

+			if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;

+			if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;

+			BN_consttime_swap(word & mask, x1, x2, group->field.top);

+			BN_consttime_swap(word & mask, z1, z2, group->field.top);

 			mask >>= 1;

 			}

 		mask = BN_TBIT;