Commit cdfe0fdd authored by Bodo Möller's avatar Bodo Möller
Browse files

Fix OPENSSL_BN_ASM_MONT5 for corner cases; add a test. 

Submitted by: Emilia Kasper
parent 59365214

crypto/bn/asm/x86_64-mont5.pl

+3 −0
Original line number Diff line number Diff line
@@ -836,6 +836,8 @@ $code.=<<___; 
.type	bn_scatter5,\@abi-omnipotent

.align	16

bn_scatter5:

	cmp	\$0, $num

	jz	.Lscatter_epilogue

	lea	($tbl,$idx,8),$tbl

.Lscatter:

	mov	($inp),%rax
@@ -844,6 +846,7 @@ bn_scatter5: 
	lea	32*8($tbl),$tbl

	sub	\$1,$num

	jnz	.Lscatter

.Lscatter_epilogue:

	ret

.size	bn_scatter5,.-bn_scatter5

___

crypto/bn/bn_exp.c

+18 −4
Original line number Diff line number Diff line
@@ -693,9 +693,6 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, 


	if (!BN_copy(&computeTemp, am)) goto err;



	if (bn_wexpand(am,top)==NULL ||	bn_wexpand(r,top)==NULL)

		goto err;



#if defined(OPENSSL_BN_ASM_MONT5)

    /* This optimization uses ideas from http://eprint.iacr.org/2011/239,

     * specifically optimization of cache-timing attack countermeasures
@@ -717,6 +714,24 @@ int BN_mod_exp_mont_consttime(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, 
	bn_scatter5(am->d,am->top,powerbuf,1);



	acc = computeTemp.d;

	/* bn_mul_mont() and bn_mul_mont_gather5() assume fixed length inputs.

	 * Pad the inputs with zeroes.

	 */

	if (bn_wexpand(am,top)==NULL ||	bn_wexpand(r,top)==NULL ||

	    bn_wexpand(&computeTemp,top)==NULL)

		goto err;

	for (i = am->top; i < top; ++i)

		{

		am->d[i] = 0;

		}

	for (i = computeTemp.top; i < top; ++i)

		{

		computeTemp.d[i] = 0;

		}

	for (i = r->top; i < top; ++i)

		{

		r->d[i] = 0;

		}

#if 0

	for (i=2; i<32; i++)

		{
@@ -1102,4 +1117,3 @@ err: 
	bn_check_top(r);

	return(ret);

	}

crypto/bn/bntest.c

+77 −0
Original line number Diff line number Diff line
@@ -107,6 +107,7 @@ int test_mod(BIO *bp,BN_CTX *ctx); 
int test_mod_mul(BIO *bp,BN_CTX *ctx);

int test_mod_exp(BIO *bp,BN_CTX *ctx);

int test_mod_exp_mont_consttime(BIO *bp,BN_CTX *ctx);

int test_mod_exp_mont5(BIO *bp, BN_CTX *ctx);

int test_exp(BIO *bp,BN_CTX *ctx);

int test_gf2m_add(BIO *bp);

int test_gf2m_mod(BIO *bp);
@@ -249,6 +250,7 @@ int main(int argc, char *argv[]) 


	message(out,"BN_mod_exp_mont_consttime");

	if (!test_mod_exp_mont_consttime(out,ctx)) goto err;

	if (!test_mod_exp_mont5(out,ctx)) goto err;

	(void)BIO_flush(out);



	message(out,"BN_exp");
@@ -1012,6 +1014,81 @@ int test_mod_exp_mont_consttime(BIO *bp, BN_CTX *ctx) 
	return(1);

	}



/* Test constant-time modular exponentiation with 1024-bit inputs,

 * which on x86_64 cause a different code branch to be taken.

 */

int test_mod_exp_mont5(BIO *bp, BN_CTX *ctx)

	{

	BIGNUM *a,*p,*m,*d,*e;

	int i;



	BN_MONT_CTX *mont;



	a=BN_new();

	p=BN_new();

	m=BN_new();

	d=BN_new();

	e=BN_new();



	mont = BN_MONT_CTX_new();



	BN_bntest_rand(m,1024,0,1); /* must be odd for montgomery */

	/* Zero exponent */

	BN_bntest_rand(a,1024,0,0);

	BN_zero(p);

	if(!BN_mod_exp_mont_consttime(d,a,p,m,ctx,NULL))

		return 0;

	if(!BN_is_one(d))

		{

		fprintf(stderr, "Modular exponentiation test failed!\n");

		return 0;

		}

	/* Zero input */

	BN_bntest_rand(p,1024,0,0);

	BN_zero(a);

	if(!BN_mod_exp_mont_consttime(d,a,p,m,ctx,NULL))

		return 0;

	if(!BN_is_zero(d))

		{

		fprintf(stderr, "Modular exponentiation test failed!\n");

		return 0;

		}

	/* Craft an input whose Montgomery representation is 1,

	 * i.e., shorter than the modulus m, in order to test

	 * the const time precomputation scattering/gathering.

	 */

	BN_one(a);

	BN_MONT_CTX_set(mont,m,ctx);

	if(!BN_from_montgomery(e,a,mont,ctx))

		return 0;

	if(!BN_mod_exp_mont_consttime(d,e,p,m,ctx,NULL))

		return 0;

	if(!BN_mod_exp_simple(a,e,p,m,ctx))

		return 0;

	if(BN_cmp(a,d) != 0)

		{

		fprintf(stderr,"Modular exponentiation test failed!\n");

		return 0;

		}

	/* Finally, some regular test vectors. */

	BN_bntest_rand(e,1024,0,0);

	if(!BN_mod_exp_mont_consttime(d,e,p,m,ctx,NULL))

		return 0;

	if(!BN_mod_exp_simple(a,e,p,m,ctx))

		return 0;

	if(BN_cmp(a,d) != 0)

		{

		fprintf(stderr,"Modular exponentiation test failed!\n");

		return 0;

		}

	BN_free(a);

	BN_free(p);

	BN_free(m);

	BN_free(d);

	BN_free(e);

	return(1);

	}



int test_exp(BIO *bp, BN_CTX *ctx)

	{

	BIGNUM *a,*b,*d,*e,*one;