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[crypto] Split out Weierstrass point initialisation and finalisation

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Prepare for adding an operation to add arbitrary curve points by
splitting out initialisation and finalisation from the multiplication
operation.

Pass explicit temporary buffer pointers to weierstrass_init() and
weierstrass_done(), to ensure that stack consumption does not increase
as a result of splitting out this functionality.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2025-12-05 16:08:49 +00:00
parent d3adea8380
commit 1e353ff361
1 changed files with 141 additions and 52 deletions
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193
src/crypto/weierstrass.c
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@@ -170,7 +170,7 @@ enum weierstrass_opcode {
*
* @v curve Weierstrass curve
*/
static void weierstrass_init ( struct weierstrass_curve *curve ) {
static void weierstrass_init_curve ( struct weierstrass_curve *curve ) {
unsigned int size = curve->size;
bigint_t ( size ) __attribute__ (( may_alias )) *prime =
( ( void * ) curve->prime[0] );
@@ -759,39 +759,33 @@ static int weierstrass_verify_raw ( const struct weierstrass_curve *curve,
} )
/**
* Multiply curve point by scalar
* Initialise curve point
*
* @v curve Weierstrass curve
* @v base Base point
* @v scalar Scalar multiple
* @v result Result point to fill in
* @v point0 Element 0 of point (x,y,z) to be filled in
* @v temp0 Element 0 of temporary point buffer
* @v data Raw curve point
* @ret rc Return status code
*/
int weierstrass_multiply ( struct weierstrass_curve *curve, const void *base,
const void *scalar, void *result ) {
static int weierstrass_init_raw ( struct weierstrass_curve *curve,
bigint_element_t *point0,
bigint_element_t *temp0, const void *data ) {
unsigned int size = curve->size;
size_t len = curve->len;
const bigint_t ( size ) __attribute__ (( may_alias )) *prime =
( ( const void * ) curve->prime[0] );
const bigint_t ( size ) __attribute__ (( may_alias )) *prime2 =
( ( const void * ) curve->prime[WEIERSTRASS_2N] );
const bigint_t ( size ) __attribute__ (( may_alias )) *fermat =
( ( const void * ) curve->fermat );
const bigint_t ( size ) __attribute__ (( may_alias )) *square =
( ( const void * ) curve->square );
const bigint_t ( size ) __attribute__ (( may_alias )) *one =
( ( const void * ) curve->one );
struct {
union {
weierstrass_t ( size ) result;
bigint_t ( size * 2 ) product_in;
};
union {
weierstrass_t ( size ) multiple;
bigint_t ( size * 2 ) product_out;
};
bigint_t ( bigint_required_size ( len ) ) scalar;
} temp;
weierstrass_t ( size ) __attribute__ (( may_alias ))
*point = ( ( void * ) point0 );
union {
bigint_t ( size * 2 ) product;
weierstrass_t ( size ) point;
} __attribute__ (( may_alias )) *temp = ( ( void * ) temp0 );
size_t offset;
unsigned int i;
int rc;
@@ -804,26 +798,140 @@ int weierstrass_multiply ( struct weierstrass_curve *curve, const void *base,
* non-zero.
*/
if ( ! prime2->element[0] )
weierstrass_init ( curve );
weierstrass_init_curve ( curve );
/* Convert input to projective coordinates in Montgomery form */
DBGC ( curve, "WEIERSTRASS %s base (", curve->name );
DBGC ( curve, "WEIERSTRASS %s point (", curve->name );
for ( i = 0, offset = 0 ; i < WEIERSTRASS_AXES ; i++, offset += len ) {
bigint_init ( &temp.multiple.axis[i], ( base + offset ), len );
bigint_init ( &point->axis[i], ( data + offset ), len );
DBGC ( curve, "%s%s", ( i ? "," : "" ),
bigint_ntoa ( &temp.multiple.axis[i] ) );
bigint_multiply ( &temp.multiple.axis[i], square,
&temp.product_in );
bigint_montgomery_relaxed ( prime, &temp.product_in,
&temp.multiple.axis[i] );
bigint_ntoa ( &point->axis[i] ) );
bigint_multiply ( &point->axis[i], square, &temp->product );
bigint_montgomery_relaxed ( prime, &temp->product,
&point->axis[i] );
}
bigint_copy ( one, &temp.multiple.z );
bigint_copy ( one, &point->z );
DBGC ( curve, ")\n" );
/* Verify point is on curve */
if ( ( rc = weierstrass_verify ( curve, &temp.multiple ) ) != 0 )
if ( ( rc = weierstrass_verify ( curve, point ) ) != 0 )
return rc;
return 0;
}
/**
* Initialise curve point
*
* @v curve Weierstrass curve
* @v point Point (x,y,z) to be filled in
* @v temp Temporary point buffer
* @v data Raw curve point
* @ret rc Return status code
*/
#define weierstrass_init( curve, point, temp, data ) ( { \
weierstrass_init_raw ( (curve), (point)->all.element, \
(temp)->all.element, (data) ); \
} )
/**
* Finalise curve point
*
* @v curve Weierstrass curve
* @v point0 Element 0 of point (x,y,z)
* @v temp0 Element 0 of temporary point buffer
* @v out Output buffer
* @ret rc Return status code
*/
static int weierstrass_done_raw ( struct weierstrass_curve *curve,
bigint_element_t *point0,
bigint_element_t *temp0, void *out ) {
unsigned int size = curve->size;
size_t len = curve->len;
const bigint_t ( size ) __attribute__ (( may_alias )) *prime =
( ( const void * ) curve->prime[0] );
const bigint_t ( size ) __attribute__ (( may_alias )) *fermat =
( ( const void * ) curve->fermat );
const bigint_t ( size ) __attribute__ (( may_alias )) *one =
( ( const void * ) curve->one );
weierstrass_t ( size ) __attribute__ (( may_alias ))
*point = ( ( void * ) point0 );
union {
bigint_t ( size * 2 ) product;
weierstrass_t ( size ) point;
} __attribute__ (( may_alias )) *temp = ( ( void * ) temp0 );
size_t offset;
unsigned int i;
/* Invert result Z co-ordinate (via Fermat's little theorem) */
bigint_copy ( one, &temp->point.z );
bigint_ladder ( &temp->point.z, &point->z, fermat,
bigint_mod_exp_ladder, prime, &temp->product );
/* Convert result back to affine co-ordinates */
DBGC ( curve, "WEIERSTRASS %s result (", curve->name );
for ( i = 0, offset = 0 ; i < WEIERSTRASS_AXES ; i++, offset += len ) {
bigint_multiply ( &point->axis[i], &temp->point.z,
&temp->product );
bigint_montgomery_relaxed ( prime, &temp->product,
&point->axis[i] );
bigint_grow ( &point->axis[i], &temp->product );
bigint_montgomery ( prime, &temp->product, &point->axis[i] );
DBGC ( curve, "%s%s", ( i ? "," : "" ),
bigint_ntoa ( &point->axis[i] ) );
bigint_done ( &point->axis[i], ( out + offset ), len );
}
DBGC ( curve, ")\n" );
/* Verify result is not the point at infinity */
if ( bigint_is_zero ( &temp->point.z ) )
return -EINVAL;
return 0;
}
/**
* Finalise curve point
*
* @v curve Weierstrass curve
* @v point Point (x,y,z)
* @v temp Temporary point buffer
* @v out Output buffer
* @ret rc Return status code
*/
#define weierstrass_done( curve, point, temp, out ) ( { \
weierstrass_done_raw ( (curve), (point)->all.element, \
(temp)->all.element, (out) ); \
} )
/**
* Multiply curve point by scalar
*
* @v curve Weierstrass curve
* @v base Base point
* @v scalar Scalar multiple
* @v result Result point to fill in
* @ret rc Return status code
*/
int weierstrass_multiply ( struct weierstrass_curve *curve, const void *base,
const void *scalar, void *result ) {
unsigned int size = curve->size;
size_t len = curve->len;
const bigint_t ( size ) __attribute__ (( may_alias )) *one =
( ( const void * ) curve->one );
struct {
weierstrass_t ( size ) result;
weierstrass_t ( size ) multiple;
bigint_t ( bigint_required_size ( len ) ) scalar;
} temp;
int rc;
/* Convert input to projective coordinates in Montgomery form */
if ( ( rc = weierstrass_init ( curve, &temp.multiple, &temp.result,
base ) ) != 0 ) {
return rc;
}
/* Construct identity element (the point at infinity) */
memset ( &temp.result, 0, sizeof ( temp.result ) );
bigint_copy ( one, &temp.result.y );
@@ -837,30 +945,11 @@ int weierstrass_multiply ( struct weierstrass_curve *curve, const void *base,
bigint_ladder ( &temp.result.all, &temp.multiple.all, &temp.scalar,
weierstrass_add_ladder, curve, NULL );
/* Invert result Z co-ordinate (via Fermat's little theorem) */
bigint_copy ( one, &temp.multiple.z );
bigint_ladder ( &temp.multiple.z, &temp.result.z, fermat,
bigint_mod_exp_ladder, prime, &temp.product_out );
/* Convert result back to affine co-ordinates */
DBGC ( curve, "WEIERSTRASS %s result (", curve->name );
for ( i = 0, offset = 0 ; i < WEIERSTRASS_AXES ; i++, offset += len ) {
bigint_multiply ( &temp.result.axis[i], &temp.multiple.z,
&temp.product_out );
bigint_montgomery_relaxed ( prime, &temp.product_out,
&temp.result.axis[i] );
bigint_grow ( &temp.result.axis[i], &temp.product_out );
bigint_montgomery ( prime, &temp.product_out,
&temp.result.axis[i] );
DBGC ( curve, "%s%s", ( i ? "," : "" ),
bigint_ntoa ( &temp.result.axis[i] ) );
bigint_done ( &temp.result.axis[i], ( result + offset ), len );
if ( ( rc = weierstrass_done ( curve, &temp.result, &temp.multiple,
result ) ) != 0 ) {
return rc;
}
DBGC ( curve, ")\n" );
/* Verify result is not the point at infinity */
if ( bigint_is_zero ( &temp.multiple.z ) )
return -EINVAL;
return 0;
}