Commit 46b695d8 authored by Bodo Möller's avatar Bodo Möller
Browse files

make RSA blinding thread-safe

parent 6076f21f

CHANGES

+7 −2
Original line number Diff line number Diff line
@@ -14,12 +14,17 @@ 
     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]

     [Ben Laurie, Steve Henson, Geoff Thorpe, Bodo Moeller]



  *) 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).

     is no point in blinding anyway).  Make RSA blinding thread-safe

     by remembering the creator's thread ID in rsa->blinding and

     having all other threads use local one-time blinding factors

     (this requires more computation than sharing rsa->blinding, but

     avoids excessive locking; and if an RSA object is not shared

     between threads, blinding will still be very fast).

     [Bodo Moeller]



  *) Fixed a typo bug that would cause ENGINE_set_default() to set an

crypto/bn/bn.h

+2 −0
Original line number Diff line number Diff line
@@ -248,6 +248,8 @@ typedef struct bn_blinding_st 
	BIGNUM *A;

	BIGNUM *Ai;

	BIGNUM *mod; /* just a reference */

	unsigned long thread_id; /* added in OpenSSL 0.9.6j and 0.9.7b;

				  * used only by crypto/rsa/rsa_eay.c, rsa_lib.c */

	} BN_BLINDING;



/* Used for montgomery multiplication */

crypto/rsa/rsa.h

+2 −2
Original line number Diff line number Diff line
@@ -158,8 +158,8 @@ 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

#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

                                              */

crypto/rsa/rsa_eay.c

+106 −8
Original line number Diff line number Diff line
@@ -214,6 +214,40 @@ static int rsa_eay_blinding(RSA *rsa, BN_CTX *ctx) 
		    err_instr \

	} while(0)



static BN_BLINDING *setup_blinding(RSA *rsa, BN_CTX *ctx)

	{

	BIGNUM *A, *Ai;

	BN_BLINDING *ret = NULL;



	/* added in OpenSSL 0.9.6j and 0.9.7b */



	/* NB: similar code appears in RSA_blinding_on (rsa_lib.c);

	 * this should be placed in a new function of its own, but for reasons

	 * of binary compatibility can't */



	BN_CTX_start(ctx);

	A = BN_CTX_get(ctx);

	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;

	ret = BN_BLINDING_new(A,Ai,rsa->n);

	BN_free(Ai);

err:

	BN_CTX_end(ctx);

	return ret;

	}



/* signing */

static int RSA_eay_private_encrypt(int flen, const unsigned char *from,

	     unsigned char *to, RSA *rsa, int padding)
@@ -222,6 +256,8 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from, 
	int i,j,k,num=0,r= -1;

	unsigned char *buf=NULL;

	BN_CTX *ctx=NULL;

	int local_blinding = 0;

	BN_BLINDING *blinding = NULL;



	BN_init(&f);

	BN_init(&ret);
@@ -259,9 +295,38 @@ static int RSA_eay_private_encrypt(int flen, const unsigned char *from, 
		}



	BLINDING_HELPER(rsa, ctx, goto err;);



	blinding = rsa->blinding;

	

	/* Now unless blinding is disabled, 'blinding' is non-NULL.

	 * But the BN_BLINDING object may be owned by some other thread

	 * (we don't want to keep it constant and we don't want to use

	 * lots of locking to avoid race conditions, so only a single

	 * thread can use it; other threads have to use local blinding

	 * factors) */

	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))

		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;

		{

		if (blinding == NULL)

			{

			RSAerr(RSA_F_RSA_EAY_PRIVATE_ENCRYPT, ERR_R_INTERNAL_ERROR);

			goto err;

			}

		}

	

	if (blinding != NULL)

		{

		if (blinding->thread_id != CRYPTO_thread_id())

			{

			/* we need a local one-time blinding factor */



			blinding = setup_blinding(rsa, ctx);

			if (blinding == NULL)

				goto err;

			local_blinding = 1;

			}

		}



	if (blinding)

		if (!BN_BLINDING_convert(&f, blinding, ctx)) goto err;



	if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||

		((rsa->p != NULL) &&
@@ -275,8 +340,8 @@ 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_NO_BLINDING))

		if (!BN_BLINDING_invert(&ret,rsa->blinding,ctx)) goto err;

	if (blinding)

		if (!BN_BLINDING_invert(&ret, blinding, ctx)) goto err;



	/* put in leading 0 bytes if the number is less than the

	 * length of the modulus */
@@ -290,6 +355,8 @@ err: 
	if (ctx != NULL) BN_CTX_free(ctx);

	BN_clear_free(&ret);

	BN_clear_free(&f);

	if (local_blinding)

		BN_BLINDING_free(blinding);

	if (buf != NULL)

		{

		OPENSSL_cleanse(buf,num);
@@ -306,6 +373,8 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from, 
	unsigned char *p;

	unsigned char *buf=NULL;

	BN_CTX *ctx=NULL;

	int local_blinding = 0;

	BN_BLINDING *blinding = NULL;



	BN_init(&f);

	BN_init(&ret);
@@ -338,9 +407,38 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from, 
		}



	BLINDING_HELPER(rsa, ctx, goto err;);



	blinding = rsa->blinding;

	

	/* Now unless blinding is disabled, 'blinding' is non-NULL.

	 * But the BN_BLINDING object may be owned by some other thread

	 * (we don't want to keep it constant and we don't want to use

	 * lots of locking to avoid race conditions, so only a single

	 * thread can use it; other threads have to use local blinding

	 * factors) */

	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))

		if (!BN_BLINDING_convert(&f,rsa->blinding,ctx)) goto err;

		{

		if (blinding == NULL)

			{

			RSAerr(RSA_F_RSA_EAY_PRIVATE_DECRYPT, ERR_R_INTERNAL_ERROR);

			goto err;

			}

		}

	

	if (blinding != NULL)

		{

		if (blinding->thread_id != CRYPTO_thread_id())

			{

			/* we need a local one-time blinding factor */



			blinding = setup_blinding(rsa, ctx);

			if (blinding == NULL)

				goto err;

			local_blinding = 1;

			}

		}



	if (blinding)

		if (!BN_BLINDING_convert(&f, blinding, ctx)) goto err;



	/* do the decrypt */

	if ( (rsa->flags & RSA_FLAG_EXT_PKEY) ||
@@ -356,8 +454,8 @@ static int RSA_eay_private_decrypt(int flen, const unsigned char *from, 
			goto err;

		}



	if (!(rsa->flags & RSA_FLAG_NO_BLINDING))

		if (!BN_BLINDING_invert(&ret,rsa->blinding,ctx)) goto err;

	if (blinding)

		if (!BN_BLINDING_invert(&ret, blinding, ctx)) goto err;



	p=buf;

	j=BN_bn2bin(&ret,p); /* j is only used with no-padding mode */

crypto/rsa/rsa_lib.c

+9 −2
Original line number Diff line number Diff line
@@ -329,6 +329,10 @@ int RSA_blinding_on(RSA *rsa, BN_CTX *p_ctx) 
	if (rsa->blinding != NULL)

		BN_BLINDING_free(rsa->blinding);



	/* NB: similar code appears in setup_blinding (rsa_eay.c);

	 * this should be placed in a new function of its own, but for reasons

	 * of binary compatibility can't */



	BN_CTX_start(ctx);

	A = BN_CTX_get(ctx);

	if ((RAND_status() == 0) && rsa->d != NULL && rsa->d->d != NULL)
@@ -345,7 +349,10 @@ int RSA_blinding_on(RSA *rsa, BN_CTX *p_ctx) 


	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);

	if ((rsa->blinding=BN_BLINDING_new(A,Ai,rsa->n)) == NULL) goto err;

	/* to make things thread-safe without excessive locking,

	 * rsa->blinding will be used just by the current thread: */

	rsa->blinding->thread_id = CRYPTO_thread_id();

	rsa->flags |= RSA_FLAG_BLINDING;

	rsa->flags &= ~RSA_FLAG_NO_BLINDING;

	BN_free(Ai);