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

enable it automatically only for the built-in engine

CHANGES

@@ -4,12 +4,18 @@
 
  Changes between 0.9.7a and 0.9.7b  [xx XXX 2003]
 
-  *) Turn on RSA blinding by default, to avoid a timing attack. Applications
+  *) Turn on RSA blinding by default in the default implementation
-     that don't want it can call RSA_blinding_off(). They would be ill-advised
+     to avoid a timing attack. Applications that don't want it can call
-     to do so in most cases. The automatic enabling can also be turned off
+     RSA_blinding_off() or use the new flag RSA_FLAG_NO_BLINDING.
-     by defining OPENSSL_FORCE_NO_RSA_BLINDING at compile-time.
+     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]
+
   *) Fixed a typo bug that would cause ENGINE_set_default() to set an
      ENGINE as defaults for all supported algorithms irrespective of
      the 'flags' parameter. 'flags' is now honoured, so applications

crypto/rsa/rsa.h

@@ -158,6 +158,11 @@ 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 0.9.7b; 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:
@@ -170,6 +175,8 @@ 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

crypto/rsa/rsa_eay.c

@@ -208,10 +208,10 @@ static int rsa_eay_blinding(RSA *rsa, BN_CTX *ctx)
 
 #define BLINDING_HELPER(rsa, ctx, err_instr) \
 	do { \
-		if(((rsa)->flags & RSA_FLAG_BLINDING) && \
+		if((!((rsa)->flags & RSA_FLAG_NO_BLINDING)) && \
-				((rsa)->blinding == NULL) && \
+		    ((rsa)->blinding == NULL) && \
-				!rsa_eay_blinding(rsa, ctx)) \
+		    !rsa_eay_blinding(rsa, ctx)) \
-			err_instr \
+		    err_instr \
 	} while(0)
 
 /* signing */
@@ -260,7 +260,7 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 
 	BLINDING_HELPER(rsa, ctx, goto err;);
 
-	if (rsa->flags & RSA_FLAG_BLINDING)
+	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
 		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
 
 	if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
@@ -275,7 +275,7 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from,
 		if (!rsa->meth->bn_mod_exp(&ret,&f,rsa->d,rsa->n,ctx,NULL)) 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
@@ -339,7 +339,7 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from,
 
 	BLINDING_HELPER(rsa, ctx, goto err;);
 
-	if (rsa->flags & RSA_FLAG_BLINDING)
+	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))
 		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;
 
 	/* do the decrypt */
@@ -356,7 +356,7 @@ 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;

crypto/rsa/rsa_lib.c

@@ -74,10 +74,6 @@ RSA *RSA_new(void)
 	{
 	RSA *r=RSA_new_method(NULL);
 
-#ifndef OPENSSL_NO_FORCE_RSA_BLINDING
-	r->flags|=RSA_FLAG_BLINDING;
-#endif
-
 	return r;
 	}
 
@@ -313,7 +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)
@@ -334,13 +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: