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Use MONT_WORD macro to control if the word-based or the bignum
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algorithm is used.
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Ulf Möller committed Feb 5, 2000
1 parent 9b14112 commit 6535eb1
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Showing 3 changed files with 95 additions and 116 deletions.
1 change: 0 additions & 1 deletion crypto/bn/bn.h
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Original file line number Diff line number Diff line change
Expand Up @@ -260,7 +260,6 @@ typedef struct bn_blinding_st
/* Used for montgomery multiplication */
typedef struct bn_mont_ctx_st
{
int use_word; /* 0 for word form, 1 for bignum form */
int ri; /* number of bits in R */
BIGNUM RR; /* used to convert to montgomery form */
BIGNUM N; /* The modulus */
Expand Down
209 changes: 95 additions & 114 deletions crypto/bn/bn_mont.c
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,8 @@
#include "cryptlib.h"
#include "bn_lcl.h"

#define MONT_WORD /* use the faster word-based algorithm */

int BN_mod_mul_montgomery(BIGNUM *r, BIGNUM *a, BIGNUM *b,
BN_MONT_CTX *mont, BN_CTX *ctx)
{
Expand Down Expand Up @@ -105,135 +107,123 @@ int BN_mod_mul_montgomery(BIGNUM *r, BIGNUM *a, BIGNUM *b,
return(0);
}

#define BN_RECURSION_MONT

int BN_from_montgomery(BIGNUM *ret, BIGNUM *a, BN_MONT_CTX *mont,
BN_CTX *ctx)
{
int retn=0;
BN_CTX_start(ctx);

#ifdef BN_RECURSION_MONT
if (mont->use_word)
#endif
{
BIGNUM *n,*r;
BN_ULONG *ap,*np,*rp,n0,v,*nrp;
int al,nl,max,i,x,ri;

if ((r = BN_CTX_get(ctx)) == NULL) goto err;
#ifdef MONT_WORD
BIGNUM *n,*r;
BN_ULONG *ap,*np,*rp,n0,v,*nrp;
int al,nl,max,i,x,ri;

if (!BN_copy(r,a)) goto err;
n= &(mont->N);
BN_CTX_start(ctx);
if ((r = BN_CTX_get(ctx)) == NULL) goto err;

ap=a->d;
/* mont->ri is the size of mont->N in bits (rounded up
to the word size) */
al=ri=mont->ri/BN_BITS2;
if (!BN_copy(r,a)) goto err;
n= &(mont->N);

nl=n->top;
if ((al == 0) || (nl == 0)) { r->top=0; return(1); }
ap=a->d;
/* mont->ri is the size of mont->N in bits (rounded up
to the word size) */
al=ri=mont->ri/BN_BITS2;

nl=n->top;
if ((al == 0) || (nl == 0)) { r->top=0; return(1); }

max=(nl+al+1); /* allow for overflow (no?) XXX */
if (bn_wexpand(r,max) == NULL) goto err;
if (bn_wexpand(ret,max) == NULL) goto err;
max=(nl+al+1); /* allow for overflow (no?) XXX */
if (bn_wexpand(r,max) == NULL) goto err;
if (bn_wexpand(ret,max) == NULL) goto err;

r->neg=a->neg^n->neg;
np=n->d;
rp=r->d;
nrp= &(r->d[nl]);
r->neg=a->neg^n->neg;
np=n->d;
rp=r->d;
nrp= &(r->d[nl]);

/* clear the top words of T */
/* clear the top words of T */
#if 1
for (i=r->top; i<max; i++) /* memset? XXX */
r->d[i]=0;
for (i=r->top; i<max; i++) /* memset? XXX */
r->d[i]=0;
#else
memset(&(r->d[r->top]),0,(max-r->top)*sizeof(BN_ULONG));
memset(&(r->d[r->top]),0,(max-r->top)*sizeof(BN_ULONG));
#endif

r->top=max;
n0=mont->n0;
r->top=max;
n0=mont->n0;

#ifdef BN_COUNT
printf("word BN_from_montgomery %d * %d\n",nl,nl);
printf("word BN_from_montgomery %d * %d\n",nl,nl);
#endif
for (i=0; i<nl; i++)
for (i=0; i<nl; i++)
{
v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
nrp++;
rp++;
if (((nrp[-1]+=v)&BN_MASK2) >= v)
continue;
else
{
v=bn_mul_add_words(rp,np,nl,(rp[0]*n0)&BN_MASK2);
nrp++;
rp++;
if (((nrp[-1]+=v)&BN_MASK2) >= v)
continue;
else
{
if (((++nrp[0])&BN_MASK2) != 0) continue;
if (((++nrp[1])&BN_MASK2) != 0) continue;
for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
}
if (((++nrp[0])&BN_MASK2) != 0) continue;
if (((++nrp[1])&BN_MASK2) != 0) continue;
for (x=2; (((++nrp[x])&BN_MASK2) == 0); x++) ;
}
bn_fix_top(r);

/* mont->ri will be a multiple of the word size */
}
bn_fix_top(r);

/* mont->ri will be a multiple of the word size */
#if 0
BN_rshift(ret,r,mont->ri);
BN_rshift(ret,r,mont->ri);
#else
x=ri;
rp=ret->d;
ap= &(r->d[x]);
if (r->top < x)
al=0;
else
al=r->top-x;
ret->top=al;
al-=4;
for (i=0; i<al; i+=4)
{
BN_ULONG t1,t2,t3,t4;

t1=ap[i+0];
t2=ap[i+1];
t3=ap[i+2];
t4=ap[i+3];
rp[i+0]=t1;
rp[i+1]=t2;
rp[i+2]=t3;
rp[i+3]=t4;
}
al+=4;
for (; i<al; i++)
rp[i]=ap[i];
x=ri;
rp=ret->d;
ap= &(r->d[x]);
if (r->top < x)
al=0;
else
al=r->top-x;
ret->top=al;
al-=4;
for (i=0; i<al; i+=4)
{
BN_ULONG t1,t2,t3,t4;
t1=ap[i+0];
t2=ap[i+1];
t3=ap[i+2];
t4=ap[i+3];
rp[i+0]=t1;
rp[i+1]=t2;
rp[i+2]=t3;
rp[i+3]=t4;
}
al+=4;
for (; i<al; i++)
rp[i]=ap[i];
#endif
#else /* !MONT_WORD */
BIGNUM *t1,*t2;

if (BN_ucmp(ret, &(mont->N)) >= 0)
{
BN_usub(ret,ret,&(mont->N)); /* XXX */
}
retn=1;
}
#ifdef BN_RECURSION_MONT
else /* bignum version */
BN_CTX_start(ctx);
t1 = BN_CTX_get(ctx);
t2 = BN_CTX_get(ctx);
if (t1 == NULL || t2 == NULL) goto err;

if (!BN_copy(t1,a)) goto err;
BN_mask_bits(t1,mont->ri);

if (!BN_mul(t2,t1,&mont->Ni,ctx)) goto err;
BN_mask_bits(t2,mont->ri);

if (!BN_mul(t1,t2,&mont->N,ctx)) goto err;
if (!BN_add(t2,a,t1)) goto err;
BN_rshift(ret,t2,mont->ri);
#endif /* MONT_WORD */

if (BN_ucmp(ret, &(mont->N)) >= 0)
{
BIGNUM *t1,*t2;

t1 = BN_CTX_get(ctx);
t2 = BN_CTX_get(ctx);
if (t1 == NULL || t2 == NULL) goto err;

if (!BN_copy(t1,a)) goto err;
BN_mask_bits(t1,mont->ri);

if (!BN_mul(t2,t1,&mont->Ni,ctx)) goto err;
BN_mask_bits(t2,mont->ri);

if (!BN_mul(t1,t2,&mont->N,ctx)) goto err;
if (!BN_add(t2,a,t1)) goto err;
BN_rshift(ret,t2,mont->ri);

if (BN_ucmp(ret,&mont->N) >= 0)
BN_usub(ret,ret,&mont->N);
retn=1;
BN_usub(ret,ret,&(mont->N));
}
#endif
retn=1;
err:
BN_CTX_end(ctx);
return(retn);
Expand All @@ -253,7 +243,6 @@ BN_MONT_CTX *BN_MONT_CTX_new(void)

void BN_MONT_CTX_init(BN_MONT_CTX *ctx)
{
ctx->use_word=0;
ctx->ri=0;
BN_init(&(ctx->RR));
BN_init(&(ctx->N));
Expand Down Expand Up @@ -281,16 +270,11 @@ int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
R= &(mont->RR); /* grab RR as a temp */
BN_copy(&(mont->N),mod); /* Set N */

#ifdef BN_RECURSION_MONT
/* the word-based algorithm is faster */
if (mont->N.top > BN_MONT_CTX_SET_SIZE_WORD)
#endif
#ifdef MONT_WORD
{
BIGNUM tmod;
BN_ULONG buf[2];

mont->use_word=1;

mont->ri=(BN_num_bits(mod)+(BN_BITS2-1))/BN_BITS2*BN_BITS2;
BN_zero(R);
BN_set_bit(R,BN_BITS2); /* R */
Expand All @@ -314,10 +298,8 @@ int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *mod, BN_CTX *ctx)
mont->n0=Ri.d[0];
BN_free(&Ri);
}
#ifdef BN_RECURSION_MONT
else
#else /* !MONT_WORD */
{ /* bignum version */
mont->use_word=0;
mont->ri=BN_num_bits(mod);
BN_zero(R);
BN_set_bit(R,mont->ri); /* R = 2^ri */
Expand Down Expand Up @@ -349,7 +331,6 @@ BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from)
BN_copy(&(to->RR),&(from->RR));
BN_copy(&(to->N),&(from->N));
BN_copy(&(to->Ni),&(from->Ni));
to->use_word=from->use_word;
to->ri=from->ri;
to->n0=from->n0;
return(to);
Expand Down
1 change: 0 additions & 1 deletion doc/crypto/BN_mod_mul_montgomery.pod
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,6 @@ The B<BN_MONT_CTX> structure is defined as follows:

typedef struct bn_mont_ctx_st
{
int use_word; /* 0 for word form, 1 for bignum form */
int ri; /* number of bits in R */
BIGNUM RR; /* R^2 (used to convert to Montgomery form) */
BIGNUM N; /* The modulus */
Expand Down

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