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Fix OPENSSL_BN_ASM_MONT5 for corner cases; add a test.

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Submitted by: Emilia Kasper
This commit is contained in:
Bodo Möller 2011-10-13 12:35:10 +00:00
parent 5936521495
commit cdfe0fdde6
3 changed files with 98 additions and 4 deletions
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3
crypto/bn/asm/x86_64-mont5.pl
View File

@ -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
___

22
crypto/bn/bn_exp.c
View File

@ -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);
}

77
crypto/bn/bntest.c
View File

@ -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;