File openssl-add-blinding-to-ecdsa.patch of Package openssl.11276

From 949ff36623eafc3523a9f91784992965018ffb05 Mon Sep 17 00:00:00 2001
From: Matt Caswell <matt@openssl.org>
Date: Fri, 25 May 2018 12:10:13 +0100
Subject: [PATCH] Add blinding to an ECDSA signature

Keegan Ryan (NCC Group) has demonstrated a side channel attack on an
ECDSA signature operation. During signing the signer calculates:

s:= k^-1 * (m + r * priv_key) mod order

The addition operation above provides a sufficient signal for a
flush+reload attack to derive the private key given sufficient signature
operations.

As a mitigation (based on a suggestion from Keegan) we add blinding to
the operation so that:

s := k^-1 * blind^-1 (blind * m + blind * r * priv_key) mod order

Since this attack is a localhost side channel only no CVE is assigned.


Added ecs_ossl.c hunk from 41d23d435221411b4d70c08b6c5424d0afcf4c19

Reviewed-by: Rich Salz <rsalz@openssl.org>
---
 CHANGES                  |  4 +++
 crypto/ecdsa/ecdsatest.c |  9 +++++-
 crypto/ecdsa/ecs_ossl.c  | 82 +++++++++++++++++++++++++++++++++++++++---------
 3 files changed, 79 insertions(+), 16 deletions(-)

Index: openssl-1.0.1i/crypto/ecdsa/ecdsatest.c
===================================================================
--- openssl-1.0.1i.orig/crypto/ecdsa/ecdsatest.c	2018-08-10 17:05:51.942549746 +0200
+++ openssl-1.0.1i/crypto/ecdsa/ecdsatest.c	2018-08-10 17:05:53.662560122 +0200
@@ -137,7 +137,7 @@ int restore_rand(void)
 		return 1;
 	}
 
-static int fbytes_counter = 0;
+static int fbytes_counter = 0, use_fake = 0;
 static const char *numbers[10] = {
 	"651056770906015076056810763456358567190100156695615665659",
 	"651056770906015076056810763456358567190100156695615665659",
@@ -160,6 +160,11 @@ int fbytes(unsigned char *buf, int num)
 	int	ret;
 	BIGNUM	*tmp = NULL;
 
+  if (use_fake == 0)
+      return old_rand->bytes(buf, num);
+
+  use_fake = 0;
+
 	if (fbytes_counter >= 10)
 		return 0;
 	tmp = BN_new();
@@ -202,11 +207,13 @@ int x9_62_test_internal(BIO *out, int ni
 	/* create the key */
 	if ((key = EC_KEY_new_by_curve_name(nid)) == NULL)
 		goto x962_int_err;
+  use_fake = 1;
 	if (!EC_KEY_generate_key(key))
 		goto x962_int_err;
 	BIO_printf(out, ".");
 	(void)BIO_flush(out);
 	/* create the signature */
+	use_fake = 1;
 	signature = ECDSA_do_sign(digest, 20, key);
 	if (signature == NULL)
 		goto x962_int_err;
Index: openssl-1.0.1i/crypto/ecdsa/ecs_ossl.c
===================================================================
--- openssl-1.0.1i.orig/crypto/ecdsa/ecs_ossl.c	2018-08-10 17:05:53.450558843 +0200
+++ openssl-1.0.1i/crypto/ecdsa/ecs_ossl.c	2018-08-10 17:17:46.074862316 +0200
@@ -223,11 +223,12 @@ err:
 }
 
 
-static ECDSA_SIG *ecdsa_do_sign(const unsigned char *dgst, int dgst_len, 
+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;
+	BIGNUM *blind = NULL, *blindm = NULL;
 	const BIGNUM *ckinv;
 	BN_CTX     *ctx = NULL;
 	const EC_GROUP   *group;
@@ -261,9 +262,19 @@ static ECDSA_SIG *ecdsa_do_sign(const un
 	}
 	s = ret->s;
 
-	if ((ctx = BN_CTX_new()) == NULL || (order = BN_new()) == NULL ||
-		(tmp = BN_new()) == NULL || (m = BN_new()) == NULL)
-	{
+	ctx = BN_CTX_new();
+	if (ctx == NULL) {
+	    ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_MALLOC_FAILURE);
+	    goto err;
+	}
+
+	BN_CTX_start(ctx);
+	order = BN_CTX_get(ctx);
+	tmp = BN_CTX_get(ctx);
+	m = BN_CTX_get(ctx);
+	blind = BN_CTX_get(ctx);
+	blindm = BN_CTX_get(ctx);
+	if (blindm == NULL) {
 		ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_MALLOC_FAILURE);
 		goto err;
 	}
@@ -311,18 +322,60 @@ static ECDSA_SIG *ecdsa_do_sign(const un
 			}
 		}
 
-		if (!BN_mod_mul(tmp, priv_key, ret->r, order, ctx))
-		{
+	  /*
+	   * The normal signature calculation is:
+	   *
+	   *   s := k^-1 * (m + r * priv_key) mod order
+	   *
+	   * We will blind this to protect against side channel attacks
+	   *
+           *   s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod order
+	   */
+
+	  /* Generate a blinding value */
+	  do {
+	      if (!BN_rand(blind, BN_num_bits(order) - 1, -1, 0))
+	          goto err;
+	  } while (BN_is_zero(blind));
+	  BN_set_flags(blind, BN_FLG_CONSTTIME);
+	  BN_set_flags(blindm, BN_FLG_CONSTTIME);
+	  BN_set_flags(tmp, BN_FLG_CONSTTIME);
+
+	  /* tmp := blind * priv_key * r mod order */
+	  if (!BN_mod_mul(tmp, blind, priv_key, order, ctx)) {
+	      ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
+	      goto err;
+	  }
+	  if (!BN_mod_mul(tmp, tmp, ret->r, order, ctx)) {
+	      ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
+	      goto err;
+	  }
+
+	  /* blindm := blind * m mod order */
+	  if (!BN_mod_mul(blindm, blind, m, order, ctx)) {
+	      ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
+	      goto err;
+	  }
+
+	  /* s : = (blind * priv_key * r) + (blind * m) mod order */
+	  if (!BN_mod_add_quick(s, tmp, blindm, order)) {
+	      ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
+	      goto err;
+	  }
+
+        /* s := s * k^-1 mod order */
+        if (!BN_mod_mul(s, s, ckinv, order, ctx)) {
 			ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
 			goto err;
 		}
-		if (!BN_mod_add_quick(s, tmp, m, order))
-		{
+
+        /* s:= s * blind^-1 mod order */
+        if (BN_mod_inverse(blind, blind, order, ctx) == NULL) {
 			ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
 			goto err;
 		}
-		if (!BN_mod_mul(s, s, ckinv, order, ctx))
-		{
+
+        if (!BN_mod_mul(s, s, blind, order, ctx)) {
 			ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
 			goto err;
 		}
@@ -349,15 +402,11 @@ err:
 		ECDSA_SIG_free(ret);
 		ret = NULL;
 	}
-	if (ctx)
+	if (ctx != NULL) {
+	  BN_CTX_end(ctx);
 		BN_CTX_free(ctx);
-	if (m)
-		BN_clear_free(m);
-	if (tmp)
-		BN_clear_free(tmp);
-	if (order)
-		BN_free(order);
-	if (kinv)
+	}
+	if (kinv != NULL)
 		BN_clear_free(kinv);
 	return ret;
 }
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