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Revision a520723f29aac6598ff0d69e34f5e9b88213e511 authored by Matt Caswell on 14 October 2016, 12:07:00 UTC, committed by Matt Caswell on 28 October 2016, 08:43:41 UTC
Ensure we have length checks for all extensions
The previous commit inspired a review of all the length checks for the
extension adding code. This adds more robust checks and adds checks where
some were missing previously. The real solution for this is to use WPACKET
which is currently in master - but that cannot be applied to release
branches.

Reviewed-by: Rich Salz <rsalz@openssl.org>
1 parent 83a1d4b
Raw File
BN_mod_mul_reciprocal.pod
=pod

=head1 NAME

BN_mod_mul_reciprocal,  BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_init,
BN_RECP_CTX_free, BN_RECP_CTX_set - modular multiplication using
reciprocal

=head1 SYNOPSIS

 #include <openssl/bn.h>

 BN_RECP_CTX *BN_RECP_CTX_new(void);
 void BN_RECP_CTX_init(BN_RECP_CTX *recp);
 void BN_RECP_CTX_free(BN_RECP_CTX *recp);

 int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);

 int BN_div_recp(BIGNUM *dv, BIGNUM *rem, BIGNUM *a, BN_RECP_CTX *recp,
        BN_CTX *ctx);

 int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
        BN_RECP_CTX *recp, BN_CTX *ctx);

=head1 DESCRIPTION

BN_mod_mul_reciprocal() can be used to perform an efficient
L<BN_mod_mul(3)|BN_mod_mul(3)> operation when the operation will be performed
repeatedly with the same modulus. It computes B<r>=(B<a>*B<b>)%B<m>
using B<recp>=1/B<m>, which is set as described below.  B<ctx> is a
previously allocated B<BN_CTX> used for temporary variables.

BN_RECP_CTX_new() allocates and initializes a B<BN_RECP> structure.
BN_RECP_CTX_init() initializes an existing uninitialized B<BN_RECP>.

BN_RECP_CTX_free() frees the components of the B<BN_RECP>, and, if it
was created by BN_RECP_CTX_new(), also the structure itself.

BN_RECP_CTX_set() stores B<m> in B<recp> and sets it up for computing
1/B<m> and shifting it left by BN_num_bits(B<m>)+1 to make it an
integer. The result and the number of bits it was shifted left will
later be stored in B<recp>.

BN_div_recp() divides B<a> by B<m> using B<recp>. It places the quotient
in B<dv> and the remainder in B<rem>.

The B<BN_RECP_CTX> structure is defined as follows:

 typedef struct bn_recp_ctx_st
	{
	BIGNUM N;	/* the divisor */
	BIGNUM Nr;	/* the reciprocal */
	int num_bits;
	int shift;
	int flags;
	} BN_RECP_CTX;

It cannot be shared between threads.

=head1 RETURN VALUES

BN_RECP_CTX_new() returns the newly allocated B<BN_RECP_CTX>, and NULL
on error.

BN_RECP_CTX_init() and BN_RECP_CTX_free() have no return values.

For the other functions, 1 is returned for success, 0 on error.
The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.

=head1 SEE ALSO

L<bn(3)|bn(3)>, L<ERR_get_error(3)|ERR_get_error(3)>, L<BN_add(3)|BN_add(3)>,
L<BN_CTX_new(3)|BN_CTX_new(3)>

=head1 HISTORY

B<BN_RECP_CTX> was added in SSLeay 0.9.0. Before that, the function
BN_reciprocal() was used instead, and the BN_mod_mul_reciprocal()
arguments were different.

=cut
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