make sure RSA blinding works when the PRNG is not properly seeded;

enable it automatically for the built-in engine

4 files changed, 63 insertions, 13 deletions

diff --git a/CHANGES b/CHANGES
index 0a5913ce15..a03875767c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -469,8 +469,19 @@
      in ssl3_get_client_key_exchange (ssl/s3_srvr.c).
      [Bodo Moeller]
 
+  *) Turn on RSA blinding by default in the default implementation
+     to avoid a timing attack. Applications that don't want it can call
+     RSA_blinding_off() or use the new flag RSA_FLAG_NO_BLINDING.
+     They would be ill-advised to do so in most cases.
+     [Ben Laurie, Steve Henson, Geoff Thorpe]
+
+  *) Change RSA blinding code so that it works when the PRNG is not
+     seeded (in this case, the secret RSA exponent is abused as
+     an unpredictable seed -- if it is not unpredictable, there
+     is no point in blinding anyway).
+     [Bodo Moeller]
+
 yet to be integrated into this CVS branch:
-- RSA blinding changes
 - Geoff's ENGINE_set_default() fix
 
   *) Target "mingw" now allows native Windows code to be generated in
diff --git a/crypto/rsa/rsa.h b/crypto/rsa/rsa.h
index b005b4b0b3..604fc26442 100644
--- a/crypto/rsa/rsa.h
+++ b/crypto/rsa/rsa.h
@@ -162,6 +162,11 @@ struct rsa_st
 #define RSA_FLAG_CACHE_PUBLIC		0x02
 #define RSA_FLAG_CACHE_PRIVATE		0x04
 #define RSA_FLAG_BLINDING		0x08
+#define RSA_FLAG_NO_BLINDING		0x80 /* new with 0.9.6j and 0.9.7b; the built-in
+                                              * RSA implementation now uses blinding by
+                                              * default (ignoring RSA_FLAG_BLINDING),
+                                              * but other engines might not need it
+                                              */
 #define RSA_FLAG_THREAD_SAFE		0x10
 /* This flag means the private key operations will be handled by rsa_mod_exp
  * and that they do not depend on the private key components being present:
@@ -174,6 +179,8 @@ struct rsa_st
  */
 #define RSA_FLAG_SIGN_VER		0x40
 
+#define RSA_FLAG_NO_BLINDING		0x80
+
 #define RSA_PKCS1_PADDING	1
 #define RSA_SSLV23_PADDING	2
 #define RSA_NO_PADDING		3
diff --git a/crypto/rsa/rsa_eay.c b/crypto/rsa/rsa_eay.c
index 24c77699fe..6bc6ef3913 100644
--- a/crypto/rsa/rsa_eay.c
+++ b/crypto/rsa/rsa_eay.c
@@ -211,6 +211,25 @@ err:
 	return(r);
 	}
 
+static int rsa_eay_blinding(RSA *rsa, BN_CTX *ctx)
+	{
+	int ret = 1;
+	CRYPTO_w_lock(CRYPTO_LOCK_RSA);
+	/* Check again inside the lock - the macro's check is racey */
+	if(rsa->blinding == NULL)
+		ret = RSA_blinding_on(rsa, ctx);
+	CRYPTO_w_unlock(CRYPTO_LOCK_RSA);
+	return ret;
+	}
+
+#define BLINDING_HELPER(rsa, ctx, err_instr) \
+	do { \
+		if((!((rsa)->flags & RSA_FLAG_NO_BLINDING)) && \
+		    ((rsa)->blinding == NULL) && \
+		    !rsa_eay_blinding(rsa, ctx)) \
+			err_instr \
+	} while(0)
+
 /* signing */
 static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 	     unsigned char *to, RSA *rsa, int padding)
@@ -255,9 +274,9 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 		goto err;
 		}
 
-	if ((rsa->flags & RSA_FLAG_BLINDING) && (rsa->blinding == NULL))
-		RSA_blinding_on(rsa,ctx);
-	if (rsa->flags & RSA_FLAG_BLINDING)
+	BLINDING_HELPER(rsa, ctx, goto err;);
+
+	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
 		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
 
 	if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
@@ -274,7 +293,7 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 				rsa->_method_mod_n)) goto err;
 		}
 
-	if (rsa->flags & RSA_FLAG_BLINDING)
+	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
 		if (!BN_BLINDING_invert(&ret,rsa->blinding,ctx)) goto err;
 
 	/* put in leading 0 bytes if the number is less than the
@@ -336,9 +355,9 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
 		goto err;
 		}
 
-	if ((rsa->flags & RSA_FLAG_BLINDING) && (rsa->blinding == NULL))
-		RSA_blinding_on(rsa,ctx);
-	if (rsa->flags & RSA_FLAG_BLINDING)
+	BLINDING_HELPER(rsa, ctx, goto err;);
+
+	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
 		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
 
 	/* do the decrypt */
@@ -357,7 +376,7 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
 			goto err;
 		}
 
-	if (rsa->flags & RSA_FLAG_BLINDING)
+	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
 		if (!BN_BLINDING_invert(&ret,rsa->blinding,ctx)) goto err;
 
 	p=buf;
diff --git a/crypto/rsa/rsa_lib.c b/crypto/rsa/rsa_lib.c
index 889c36d3a6..33ca8330c9 100644
--- a/crypto/rsa/rsa_lib.c
+++ b/crypto/rsa/rsa_lib.c
@@ -72,7 +72,9 @@ static const RSA_METHOD *default_RSA_meth=NULL;
 
 RSA *RSA_new(void)
 	{
-	return(RSA_new_method(NULL));
+	RSA *r=RSA_new_method(NULL);
+
+	return r;
 	}
 
 void RSA_set_default_method(const RSA_METHOD *meth)
@@ -307,7 +309,8 @@ void RSA_blinding_off(RSA *rsa)
 		BN_BLINDING_free(rsa->blinding);
 		rsa->blinding=NULL;
 		}
-	rsa->flags&= ~RSA_FLAG_BLINDING;
+	rsa->flags &= ~RSA_FLAG_BLINDING;
+	rsa->flags |= RSA_FLAG_NO_BLINDING;
 	}
 
 int RSA_blinding_on(RSA *rsa, BN_CTX *p_ctx)
@@ -328,13 +331,23 @@ int RSA_blinding_on(RSA *rsa, BN_CTX *p_ctx)
 
 	BN_CTX_start(ctx);
 	A = BN_CTX_get(ctx);
-	if (!BN_rand_range(A,rsa->n)) goto err;
+	if ((RAND_status() == 0) && rsa->d != NULL && rsa->d->d != NULL)
+		{
+		/* if PRNG is not properly seeded, resort to secret exponent as unpredictable seed */
+		RAND_add(rsa->d->d, rsa->d->dmax * sizeof rsa->d->d[0], 0);
+		if (!BN_pseudo_rand_range(A,rsa->n)) goto err;
+		}
+	else
+		{
+		if (!BN_rand_range(A,rsa->n)) goto err;
+		}
 	if ((Ai=BN_mod_inverse(NULL,A,rsa->n,ctx)) == NULL) goto err;
 
 	if (!rsa->meth->bn_mod_exp(A,A,rsa->e,rsa->n,ctx,rsa->_method_mod_n))
 	    goto err;
 	rsa->blinding=BN_BLINDING_new(A,Ai,rsa->n);
-	rsa->flags|=RSA_FLAG_BLINDING;
+	rsa->flags |= RSA_FLAG_BLINDING;
+	rsa->flags &= ~RSA_FLAG_NO_BLINDING;
 	BN_free(Ai);
 	ret=1;
 err: