portable_bignum.cpp File Reference

Software Montgomery modexp - the bignum backend for a vendor with no accelerator. More...

#include "board_drivers/board_profiles/pc_platform.h"
#include "crypto/asymmetric/bignum.h"
#include "crypto/crypto_opt.h"
#include "server/mmgr/secure.h"
#include <string.h>

Go to the source code of this file.

Classes
struct	PC_CRYPTO_HOT::Group14Ctx

Namespaces
namespace	PC_CRYPTO_HOT

Functions
void	bn_expmod_group14 (pc_bignum *out, const pc_bignum *base, const pc_bignum *exp)

Detailed Description

Software Montgomery modexp - the bignum backend for a vendor with no accelerator.

Selected EXPLICITLY by a vendor profile that sets PC_HAS_HW_BIGNUM 0. It is never a fallback: the core declares bn_expmod_group14() and links whatever backend the vendor provides, so linking none is an undefined reference and linking two is a duplicate definition. Both fail the build.

Software crypto is a legitimate choice and on some parts the only one - what must not happen is arriving here by default. This implementation is data-dependent and NOT constant time (SECURITY.md, timing), so a vendor whose silicon can do the modexp in hardware must never end up on it silently; with no weak symbol anywhere in the chain, it cannot.

Definition in file portable_bignum.cpp.

Function Documentation

bn_expmod_group14()

void bn_expmod_group14	(	pc_bignum *	out,
		const pc_bignum *	base,
		const pc_bignum *	exp
	)

Definition at line 195 of file portable_bignum.cpp.

References pc_span::buf, pc_bignum::d, PC_BN_LIMBS, pc_span_ok(), PC_CRYPTO_HOT::Group14Ctx::r1, PC_CRYPTO_HOT::Group14Ctx::r2, and SecureBorrow::span().

Referenced by ssh_dh_generate(), and ssh_kexdh_handle().