BN_INTERNAL(3) OpenSSL BN_INTERNAL(3)NAME
bn_mul_words, bn_mul_add_words, bn_sqr_words, bn_div_words,
bn_add_words, bn_sub_words, bn_mul_comba4, bn_mul_comba8,
bn_sqr_comba4, bn_sqr_comba8, bn_cmp_words, bn_mul_normal,
bn_mul_low_normal, bn_mul_recursive, bn_mul_part_recursive,
bn_mul_low_recursive, bn_mul_high, bn_sqr_normal,
bn_sqr_recursive, bn_expand, bn_wexpand, bn_expand2,
bn_fix_top, bn_check_top, bn_print, bn_dump, bn_set_max,
bn_set_high, bn_set_low - BIGNUM library internal functions
SYNOPSIS
BN_ULONG bn_mul_words(BN_ULONG *rp, BN_ULONG *ap, int num, BN_ULONG w);
BN_ULONG bn_mul_add_words(BN_ULONG *rp, BN_ULONG *ap, int num,
BN_ULONG w);
void bn_sqr_words(BN_ULONG *rp, BN_ULONG *ap, int num);
BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d);
BN_ULONG bn_add_words(BN_ULONG *rp, BN_ULONG *ap, BN_ULONG *bp,
int num);
BN_ULONG bn_sub_words(BN_ULONG *rp, BN_ULONG *ap, BN_ULONG *bp,
int num);
void bn_mul_comba4(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b);
void bn_mul_comba8(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b);
void bn_sqr_comba4(BN_ULONG *r, BN_ULONG *a);
void bn_sqr_comba8(BN_ULONG *r, BN_ULONG *a);
int bn_cmp_words(BN_ULONG *a, BN_ULONG *b, int n);
void bn_mul_normal(BN_ULONG *r, BN_ULONG *a, int na, BN_ULONG *b,
int nb);
void bn_mul_low_normal(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n);
void bn_mul_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n2,
int dna,int dnb,BN_ULONG *tmp);
void bn_mul_part_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b,
int n, int tna,int tnb, BN_ULONG *tmp);
void bn_mul_low_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b,
int n2, BN_ULONG *tmp);
void bn_mul_high(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, BN_ULONG *l,
int n2, BN_ULONG *tmp);
void bn_sqr_normal(BN_ULONG *r, BN_ULONG *a, int n, BN_ULONG *tmp);
void bn_sqr_recursive(BN_ULONG *r, BN_ULONG *a, int n2, BN_ULONG *tmp);
void mul(BN_ULONG r, BN_ULONG a, BN_ULONG w, BN_ULONG c);
void mul_add(BN_ULONG r, BN_ULONG a, BN_ULONG w, BN_ULONG c);
void sqr(BN_ULONG r0, BN_ULONG r1, BN_ULONG a);
BIGNUM *bn_expand(BIGNUM *a, int bits);
BIGNUM *bn_wexpand(BIGNUM *a, int n);
BIGNUM *bn_expand2(BIGNUM *a, int n);
void bn_fix_top(BIGNUM *a);
MirOS BSD #10-current 2005-02-05 1
BN_INTERNAL(3) OpenSSL BN_INTERNAL(3)
void bn_check_top(BIGNUM *a);
void bn_print(BIGNUM *a);
void bn_dump(BN_ULONG *d, int n);
void bn_set_max(BIGNUM *a);
void bn_set_high(BIGNUM *r, BIGNUM *a, int n);
void bn_set_low(BIGNUM *r, BIGNUM *a, int n);
DESCRIPTION
This page documents the internal functions used by the
OpenSSL BIGNUM implementation. They are described here to
facilitate debugging and extending the library. They are not
to be used by applications.
The BIGNUM structure
typedef struct bignum_st
{
int top; /* index of last used d (most significant word) */
BN_ULONG *d; /* pointer to an array of 'BITS2' bit chunks */
int max; /* size of the d array */
int neg; /* sign */
} BIGNUM;
The big number is stored in d, a malloc()ed array of
BN_ULONGs, least significant first. A BN_ULONG can be either
16, 32 or 64 bits in size (BITS2), depending on the 'number
of bits' specified in "openssl/bn.h".
max is the size of the d array that has been allocated. top
is the 'last' entry being used, so for a value of 4,
bn.d[0]=4 and bn.top=1. neg is 1 if the number is negative.
When a BIGNUM is 0, the d field can be NULL and top == 0.
Various routines in this library require the use of tem-
porary BIGNUM variables during their execution. Since
dynamic memory allocation to create BIGNUMs is rather expen-
sive when used in conjunction with repeated subroutine
calls, the BN_CTX structure is used. This structure con-
tains BN_CTX_NUM BIGNUMs, see BN_CTX_start(3).
Low-level arithmetic operations
These functions are implemented in C and for several plat-
forms in assembly language:
bn_mul_words(rp, ap, num, w) operates on the num word arrays
rp and ap. It computes ap * w, places the result in rp, and
returns the high word (carry).
bn_mul_add_words(rp, ap, num, w) operates on the num word
arrays rp and ap. It computes ap * w + rp, places the
result in rp, and returns the high word (carry).
MirOS BSD #10-current 2005-02-05 2
BN_INTERNAL(3) OpenSSL BN_INTERNAL(3)
bn_sqr_words(rp, ap, n) operates on the num word array ap
and the 2*num word array ap. It computes ap * ap word-wise,
and places the low and high bytes of the result in rp.
bn_div_words(h, l, d) divides the two word number (h,l) by d
and returns the result.
bn_add_words(rp, ap, bp, num) operates on the num word
arrays ap, bp and rp. It computes ap + bp, places the
result in rp, and returns the high word (carry).
bn_sub_words(rp, ap, bp, num) operates on the num word
arrays ap, bp and rp. It computes ap - bp, places the
result in rp, and returns the carry (1 if bp > ap, 0 other-
wise).
bn_mul_comba4(r, a, b) operates on the 4 word arrays a and b
and the 8 word array r. It computes a*b and places the
result in r.
bn_mul_comba8(r, a, b) operates on the 8 word arrays a and b
and the 16 word array r. It computes a*b and places the
result in r.
bn_sqr_comba4(r, a, b) operates on the 4 word arrays a and b
and the 8 word array r.
bn_sqr_comba8(r, a, b) operates on the 8 word arrays a and b
and the 16 word array r.
The following functions are implemented in C:
bn_cmp_words(a, b, n) operates on the n word arrays a and b.
It returns 1, 0 and -1 if a is greater than, equal and less
than b.
bn_mul_normal(r, a, na, b, nb) operates on the na word array
a, the nb word array b and the na+nb word array r. It com-
putes a*b and places the result in r.
bn_mul_low_normal(r, a, b, n) operates on the n word arrays
r, a and b. It computes the n low words of a*b and places
the result in r.
bn_mul_recursive(r, a, b, n2, dna, dnb, t) operates on the
word arrays a and b of length n2+dna and n2+dnb (dna and dnb
are currently allowed to be 0 or negative) and the 2*n2 word
arrays r and t. n2 must be a power of 2. It computes a*b
and places the result in r.
bn_mul_part_recursive(r, a, b, n, tna, tnb, tmp) operates on
the word arrays a and b of length n+tna and n+tnb and the
MirOS BSD #10-current 2005-02-05 3
BN_INTERNAL(3) OpenSSL BN_INTERNAL(3)
4*n word arrays r and tmp.
bn_mul_low_recursive(r, a, b, n2, tmp) operates on the n2
word arrays r and tmp and the n2/2 word arrays a and b.
bn_mul_high(r, a, b, l, n2, tmp) operates on the n2 word
arrays r, a, b and l (?) and the 3*n2 word array tmp.
BN_mul() calls bn_mul_normal(), or an optimized implementa-
tion if the factors have the same size: bn_mul_comba8() is
used if they are 8 words long, bn_mul_recursive() if they
are larger than BN_MULL_SIZE_NORMAL and the size is an exact
multiple of the word size, and bn_mul_part_recursive() for
others that are larger than BN_MULL_SIZE_NORMAL.
bn_sqr_normal(r, a, n, tmp) operates on the n word array a
and the 2*n word arrays tmp and r.
The implementations use the following macros which, depend-
ing on the architecture, may use "long long" C operations or
inline assembler. They are defined in "bn_lcl.h".
mul(r, a, w, c) computes w*a+c and places the low word of
the result in r and the high word in c.
mul_add(r, a, w, c) computes w*a+r+c and places the low word
of the result in r and the high word in c.
sqr(r0, r1, a) computes a*a and places the low word of the
result in r0 and the high word in r1.
Size changes
bn_expand() ensures that b has enough space for a bits bit
number. bn_wexpand() ensures that b has enough space for an
n word number. If the number has to be expanded, both mac-
ros call bn_expand2(), which allocates a new d array and
copies the data. They return NULL on error, b otherwise.
The bn_fix_top() macro reduces a->top to point to the most
significant non-zero word when a has shrunk.
Debugging
bn_check_top() verifies that "((a)->top >= 0 && (a)->top <=
(a)->max)". A violation will cause the program to abort.
bn_print() prints a to stderr. bn_dump() prints n words at d
(in reverse order, i.e. most significant word first) to
stderr.
MirOS BSD #10-current 2005-02-05 4
BN_INTERNAL(3) OpenSSL BN_INTERNAL(3)bn_set_max() makes a a static number with a max of its
current size. This is used by bn_set_low() and bn_set_high()
to make r a read-only BIGNUM that contains the n low or high
words of a.
If BN_DEBUG is not defined, bn_check_top(), bn_print(),
bn_dump() and bn_set_max() are defined as empty macros.
SEE ALSObn(3)MirOS BSD #10-current 2005-02-05 5
