untrusted comment: verify with openbsd-63-base.pub
RWRxzbLwAd76ZQQlFRNKEfNompyJ2JhzSXXR7R2d9+Gs4IkEE7ZPyqk7JCTYl6cPwM/erVz13PKZwUJ9JVYTDn+7FdHLb13DAQI=

OpenBSD 6.3 errata 022, November 17, 2018:

Timing side channels may leak information about DSA and ECDSA private
keys.

Apply by doing:
    signify -Vep /etc/signify/openbsd-63-base.pub -x 022_blinding.patch.sig \
        -m - | (cd /usr/src && patch -p0)

And then rebuild and install libcrypto
    cd /usr/src/lib/libcrypto
    make obj
    make
    make install

Index: lib/libcrypto/dsa/dsa_ossl.c
===================================================================
RCS file: /var/cvs/src/lib/libcrypto/dsa/dsa_ossl.c,v
retrieving revision 1.30.2.1
diff -u -p -r1.30.2.1 dsa_ossl.c
--- lib/libcrypto/dsa/dsa_ossl.c	13 Jun 2018 15:08:08 -0000	1.30.2.1
+++ lib/libcrypto/dsa/dsa_ossl.c	11 Nov 2018 16:13:33 -0000
@@ -94,16 +94,17 @@ DSA_OpenSSL(void)
 static DSA_SIG *
 dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
 {
-	BIGNUM *kinv = NULL, *r = NULL, *s = NULL;
-	BIGNUM m;
-	BIGNUM xr;
+	BIGNUM b, bm, bxr, binv, m, *kinv = NULL, *r = NULL, *s = NULL;
 	BN_CTX *ctx = NULL;
 	int reason = ERR_R_BN_LIB;
 	DSA_SIG *ret = NULL;
 	int noredo = 0;
 
+	BN_init(&b);
+	BN_init(&binv);
+	BN_init(&bm);
+	BN_init(&bxr);
 	BN_init(&m);
-	BN_init(&xr);
 
 	if (!dsa->p || !dsa->q || !dsa->g) {
 		reason = DSA_R_MISSING_PARAMETERS;
@@ -139,10 +140,36 @@ redo:
 	if (BN_bin2bn(dgst,dlen,&m) == NULL)
 		goto err;
 
-	/* Compute  s = inv(k) (m + xr) mod q */
-	if (!BN_mod_mul(&xr, dsa->priv_key, r, dsa->q, ctx))	/* s = xr */
+	/*
+	 * Compute:
+	 *
+	 *  s = inv(k)(m + xr) mod q
+	 *
+	 * In order to reduce the possibility of a side-channel attack, the
+	 * following is calculated using a blinding value:
+	 *
+	 *  s = inv(k)inv(b)(bm + bxr) mod q
+	 *
+	 * Where b is a random value in the range [1, q-1].
+	 */
+	if (!BN_sub(&bm, dsa->q, BN_value_one()))
+		goto err;
+	if (!BN_rand_range(&b, &bm))
+		goto err;
+	if (!BN_add(&b, &b, BN_value_one()))
+		goto err;
+	if (BN_mod_inverse_ct(&binv, &b, dsa->q, ctx) == NULL)
+		goto err;
+
+	if (!BN_mod_mul(&bxr, &b, dsa->priv_key, dsa->q, ctx))	/* bx */
+		goto err;
+	if (!BN_mod_mul(&bxr, &bxr, r, dsa->q, ctx))		/* bxr */
+		goto err;
+	if (!BN_mod_mul(&bm, &b, &m, dsa->q, ctx))		/* bm */
+		goto err;
+	if (!BN_mod_add(s, &bxr, &bm, dsa->q, ctx))		/* s = bm + bxr */
 		goto err;
-	if (!BN_mod_add(s, &xr, &m, dsa->q, ctx))		/* s = m + xr */
+	if (!BN_mod_mul(s, s, &binv, dsa->q, ctx))		/* s = m + xr */
 		goto err;
 	if (!BN_mod_mul(s, s, kinv, dsa->q, ctx))
 		goto err;
@@ -171,8 +198,11 @@ err:
 		BN_free(s);
 	}
 	BN_CTX_free(ctx);
+	BN_clear_free(&b);
+	BN_clear_free(&bm);
+	BN_clear_free(&bxr);
+	BN_clear_free(&binv);
 	BN_clear_free(&m);
-	BN_clear_free(&xr);
 	BN_clear_free(kinv);
 	return ret;
 }
Index: lib/libcrypto/ecdsa/ecs_ossl.c
===================================================================
RCS file: /var/cvs/src/lib/libcrypto/ecdsa/ecs_ossl.c,v
retrieving revision 1.9.2.1
diff -u -p -r1.9.2.1 ecs_ossl.c
--- lib/libcrypto/ecdsa/ecs_ossl.c	13 Jun 2018 15:08:08 -0000	1.9.2.1
+++ lib/libcrypto/ecdsa/ecs_ossl.c	11 Nov 2018 16:13:48 -0000
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecs_ossl.c,v 1.9.2.1 2018/06/13 15:08:08 jsing Exp $ */
+/* $OpenBSD: ecs_ossl.c,v 1.12 2018/06/14 18:51:01 tb Exp $ */
 /*
  * Written by Nils Larsch for the OpenSSL project
  */
@@ -204,14 +204,14 @@ static ECDSA_SIG *
 ecdsa_do_sign(const unsigned char *dgst, int dgst_len,
     const BIGNUM *in_kinv, const BIGNUM *in_r, EC_KEY *eckey)
 {
-	int     ok = 0, i;
-	BIGNUM *kinv = NULL, *s, *m = NULL, *tmp = NULL, *order = NULL;
-	const BIGNUM *ckinv;
-	BN_CTX     *ctx = NULL;
-	const EC_GROUP   *group;
+	BIGNUM *b = NULL, *binv = NULL, *bm = NULL, *bxr = NULL;
+	BIGNUM *kinv = NULL, *m = NULL, *order = NULL, *range = NULL, *s;
+	const BIGNUM *ckinv, *priv_key;
+	BN_CTX *ctx = NULL;
+	const EC_GROUP *group;
 	ECDSA_SIG  *ret;
 	ECDSA_DATA *ecdsa;
-	const BIGNUM *priv_key;
+	int     ok = 0, i;
 
 	ecdsa = ecdsa_check(eckey);
 	group = EC_KEY_get0_group(eckey);
@@ -230,7 +230,9 @@ ecdsa_do_sign(const unsigned char *dgst,
 	s = ret->s;
 
 	if ((ctx = BN_CTX_new()) == NULL || (order = BN_new()) == NULL ||
-	    (tmp = BN_new()) == NULL || (m = BN_new()) == NULL) {
+	    (range = BN_new()) == NULL || (b = BN_new()) == NULL ||
+	    (binv = BN_new()) == NULL || (bm = BN_new()) == NULL ||
+	    (bxr = BN_new()) == NULL || (m = BN_new()) == NULL) {
 		ECDSAerror(ERR_R_MALLOC_FAILURE);
 		goto err;
 	}
@@ -269,11 +271,53 @@ ecdsa_do_sign(const unsigned char *dgst,
 			}
 		}
 
-		if (!BN_mod_mul(tmp, priv_key, ret->r, order, ctx)) {
+		/*
+		 * Compute s = inv(k)(m + xr) mod order.
+		 *
+		 * In order to reduce the possibility of a side-channel attack,
+		 * the following is calculated using a blinding value:
+		 *
+		 *  s = inv(k)inv(b)(bm + bxr) mod order
+		 *
+		 * where b is a random value in the range [1, order-1].
+		 */
+		
+		/* Generate b in range [1, order-1]. */
+		if (!BN_sub(range, order, BN_value_one())) {
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+		if (!BN_rand_range(b, range)) {
 			ECDSAerror(ERR_R_BN_LIB);
 			goto err;
 		}
-		if (!BN_mod_add(s, tmp, m, order, ctx)) {
+		if (!BN_add(b, b, BN_value_one())) {
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+
+		if (BN_mod_inverse_ct(binv, b, order, ctx) == NULL) {
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+
+		if (!BN_mod_mul(bxr, b, priv_key, order, ctx)) { /* bx */
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+		if (!BN_mod_mul(bxr, bxr, ret->r, order, ctx)) { /* bxr */
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+		if (!BN_mod_mul(bm, b, m, order, ctx)) { /* bm */
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+		if (!BN_mod_add(s, bm, bxr, order, ctx)) { /* s = bm + bxr */
+			ECDSAerror(ERR_R_BN_LIB);
+			goto err;
+		}
+		if (!BN_mod_mul(s, s, binv, order, ctx)) { /* s = m + xr */
 			ECDSAerror(ERR_R_BN_LIB);
 			goto err;
 		}
@@ -281,9 +325,12 @@ ecdsa_do_sign(const unsigned char *dgst,
 			ECDSAerror(ERR_R_BN_LIB);
 			goto err;
 		}
+
 		if (BN_is_zero(s)) {
-			/* if kinv and r have been supplied by the caller
-			 * don't to generate new kinv and r values */
+			/*
+			 * If kinv and r have been supplied by the caller,
+			 * don't generate new kinv and r values
+			 */
 			if (in_kinv != NULL && in_r != NULL) {
 				ECDSAerror(ECDSA_R_NEED_NEW_SETUP_VALUES);
 				goto err;
@@ -301,10 +348,14 @@ err:
 		ret = NULL;
 	}
 	BN_CTX_free(ctx);
+	BN_clear_free(b);
+	BN_clear_free(binv);
+	BN_clear_free(bm);
+	BN_clear_free(bxr);
+	BN_clear_free(kinv);
 	BN_clear_free(m);
-	BN_clear_free(tmp);
 	BN_free(order);
-	BN_clear_free(kinv);
+	BN_free(range);
 	return ret;
 }