path: root/lib/libcrypto/man/bn_dump.3

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.Dd $Mdocdate: November 16 2023 $
.Dt BN_DUMP 3
.Os
.Sh NAME
.Nm bn_mul_words ,
.Nm bn_mul_add_words ,
.Nm bn_sqr_words ,
.Nm bn_div_words ,
.Nm bn_add_words ,
.Nm bn_sub_words ,
.Nm bn_mul_comba4 ,
.Nm bn_mul_comba8 ,
.Nm bn_sqr_comba4 ,
.Nm bn_sqr_comba8 ,
.Nm bn_mul_normal ,
.Nm bn_expand ,
.Nm bn_wexpand
.Nd BIGNUM library internal functions
.Sh SYNOPSIS
.Fd #include "bn_local.h"
.Ft BN_ULONG
.Fo bn_mul_words
.Fa "BN_ULONG *rp"
.Fa "BN_ULONG *ap"
.Fa "int num"
.Fa "BN_ULONG w"
.Fc
.Ft BN_ULONG
.Fo bn_mul_add_words
.Fa "BN_ULONG *rp"
.Fa "BN_ULONG *ap"
.Fa "int num"
.Fa "BN_ULONG w"
.Fc
.Ft void
.Fo bn_sqr_words
.Fa "BN_ULONG *rp"
.Fa "BN_ULONG *ap"
.Fa "int num"
.Fc
.Ft BN_ULONG
.Fo bn_div_words
.Fa "BN_ULONG h"
.Fa "BN_ULONG l"
.Fa "BN_ULONG d"
.Fc
.Ft BN_ULONG
.Fo bn_add_words
.Fa "BN_ULONG *rp"
.Fa "BN_ULONG *ap"
.Fa "BN_ULONG *bp"
.Fa "int num"
.Fc
.Ft BN_ULONG
.Fo bn_sub_words
.Fa "BN_ULONG *rp"
.Fa "BN_ULONG *ap"
.Fa "BN_ULONG *bp"
.Fa "int num"
.Fc
.Ft void
.Fo bn_mul_comba4
.Fa "BN_ULONG *r"
.Fa "BN_ULONG *a"
.Fa "BN_ULONG *b"
.Fc
.Ft void
.Fo bn_mul_comba8
.Fa "BN_ULONG *r"
.Fa "BN_ULONG *a"
.Fa "BN_ULONG *b"
.Fc
.Ft void
.Fo bn_sqr_comba4
.Fa "BN_ULONG *r"
.Fa "BN_ULONG *a"
.Fc
.Ft void
.Fo bn_sqr_comba8
.Fa "BN_ULONG *r"
.Fa "BN_ULONG *a"
.Fc
.Ft void
.Fo bn_mul_normal
.Fa "BN_ULONG *r"
.Fa "BN_ULONG *a"
.Fa "int na"
.Fa "BN_ULONG *b"
.Fa "int nb"
.Fc
.Ft BIGNUM *
.Fo bn_expand
.Fa "BIGNUM *a"
.Fa "int bits"
.Fc
.Ft BIGNUM *
.Fo bn_wexpand
.Fa "BIGNUM *a"
.Fa "int n"
.Fc
.Sh DESCRIPTION
This page documents some internal functions used by the
.Vt BIGNUM
implementation.
They are described here to facilitate debugging and extending the
library.
They are
.Em not
to be used by applications.
.Ss The BIGNUM structure
.Bd -literal
typedef struct bignum_st BIGNUM;

struct bignum_st {
	BN_ULONG *d;	/* Pointer to an array of 'BN_BITS2' bit chunks. */
	int top;	/* Index of last used d +1. */
	/* The next are internal book keeping for bn_expand. */
	int dmax;	/* Size of the d array. */
	int neg;	/* one if the number is negative */
	int flags;
};
.Ed
.Pp
The integer value is stored in
.Fa d ,
a
.Xr malloc 3 Ap ed
array of words
.Pq Vt BN_ULONG ,
least significant word first.
.Vt BN_ULONG
is a macro that expands to
.Vt unsigned long Pq = Vt uint64_t
on
.Dv _LP64
platforms and
.Vt unsigned int Pq = Vt uint32_t
elsewhere.
.Pp
.Fa dmax
is the size of the
.Fa d
array that has been allocated.
.Fa top
is the number of words being used, so for a value of 4, bn.d[0]=4 and
bn.top=1.
.Fa neg
is 1 if the number is negative.
When a
.Vt BIGNUM
is 0, the
.Fa d
field can be
.Dv NULL
and
.Fa top
== 0.
.Pp
.Fa flags
is a bit field of flags which are defined in
.In openssl/bn.h .
The flags begin with
.Dv BN_FLG_ .
The functions
.Xr BN_set_flags 3
and
.Xr BN_get_flags 3
enable or inspect
.Fa flags .
.Pp
Various routines in this library require the use of temporary
.Vt BIGNUM
variables during their execution.
Since dynamic memory allocation to create
.Vt BIGNUM Ns s
is rather expensive when used in conjunction with repeated subroutine
calls, the
.Vt BN_CTX
structure is used.
This structure contains BN_CTX_NUM
.Vt BIGNUM Ns s ;
see
.Xr BN_CTX_start 3 .
.Ss Low level arithmetic operations
These functions are implemented in C and for several platforms in
assembly language:
.Pp
.Fn bn_mul_words rp ap num w
operates on the
.Fa num
word arrays
.Fa rp
and
.Fa ap .
It computes
.Fa ap
*
.Fa w ,
places the result in
.Fa rp ,
and returns the high word (carry).
.Pp
.Fn bn_mul_add_words rp ap num w
operates on the
.Fa num
word arrays
.Fa rp
and
.Fa ap .
It computes
.Fa ap
*
.Fa w
+
.Fa rp ,
places the result in
.Fa rp ,
and returns the high word (carry).
.Pp
.Fn bn_sqr_words rp ap num
operates on the
.Fa num
word array
.Fa ap
and the
.Pf 2* Fa num
word array
.Fa ap .
It computes
.Fa ap
*
.Fa ap
word-wise, and places the low and high bytes of the result in
.Fa rp .
.Pp
.Fn bn_div_words h l d
divides the two word number
.Pq Fa h , Fa l
by
.Fa d
and returns the result.
.Pp
.Fn bn_add_words rp ap bp num
operates on the
.Fa num
word arrays
.Fa ap ,
.Fa bp
and
.Fa rp .
It computes
.Fa ap
+
.Fa bp ,
places the result in
.Fa rp ,
and returns the high word (carry).
.Pp
.Fn bn_sub_words rp ap bp num
operates on the
.Fa num
word arrays
.Fa ap ,
.Fa bp
and
.Fa rp .
It computes
.Fa ap
-
.Fa bp ,
places the result in
.Fa rp ,
and returns the carry (1 if
.Fa bp
\(ra
.Fa ap ,
0 otherwise).
.Pp
.Fn bn_mul_comba4 r a b
operates on the 4 word arrays
.Fa a
and
.Fa b
and the 8-word array
.Fa r .
It computes
.Fa a Ns * Ns Fa b
and places the result in
.Fa r .
.Pp
.Fn bn_mul_comba8 r a b
operates on the 8-word arrays
.Fa a
and
.Fa b
and the 16-word array
.Fa r .
It computes
.Fa a Ns * Ns Fa b
and places the result in
.Fa r .
.Pp
.Fn bn_sqr_comba4 r a b
operates on the 4-word arrays
.Fa a
and
.Fa b
and the 8-word array
.Fa r .
.Pp
.Fn bn_sqr_comba8 r a b
operates on the 8-word arrays
.Fa a
and
.Fa b
and the 16 word array
.Fa r .
.Pp
The following functions are implemented in C:
.Pp
.Fn bn_mul_normal r a na b nb
operates on the
.Fa na
word array
.Fa a ,
the
.Fa nb
word array
.Fa b
and the
.Fa na Ns + Ns Fa nb
word array
.Fa r .
It computes
.Fa a Ns * Ns Fa b
and places the result in
.Fa r .
.Pp
.Xr BN_mul 3
calls
.Fn bn_mul_comba4
if both factors are 4 words long,
.Fn bn_mul_comba8
if both factors are 8 words long,
or
.Fn bn_mul_normal
otherwise.
.Ss Size changes
.Fn bn_expand
ensures that
.Fa b
has enough space for a
.Fa bits
bit number.
.Fn bn_wexpand
ensures that
.Fa b
has enough space for an
.Fa n
word number.
They return 0 on error or 1 otherwise.
.Sh SEE ALSO
.Xr BN_new 3