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Make _optionally_safe functions internal

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The complexity of having functions whose security properties depend on a
runtime argument can be dangerous. Limit misuse by making any such
functions local.

Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2024-08-12 18:20:59 +01:00 committed by Manuel Pégourié-Gonnard
parent 91537eb09d
commit 9a8b1f4a4c
4 changed files with 62 additions and 34 deletions
tf-psa-crypto/drivers/builtin
include/mbedtls
bignum.h
src
bignum.cbignum_core.cbignum_core.h

8
tf-psa-crypto/drivers/builtin/include/mbedtls/bignum.h

@ -903,6 +903,8 @@ int mbedtls_mpi_mod_int(mbedtls_mpi_uint *r, const mbedtls_mpi *A,
/**
* \brief Perform a modular exponentiation: X = A^E mod N
*
* \warning This function is not constant time with respect to \p E (the exponent).
*
* \param X The destination MPI. This must point to an initialized MPI.
* This must not alias E or N.
* \param A The base of the exponentiation.
@ -927,9 +929,9 @@ int mbedtls_mpi_mod_int(mbedtls_mpi_uint *r, const mbedtls_mpi *A,
* \return Another negative error code on different kinds of failures.
*
*/
int mbedtls_mpi_exp_mod_optionally_safe(mbedtls_mpi *X, const mbedtls_mpi *A,
const mbedtls_mpi *E, const mbedtls_mpi *N,
mbedtls_mpi *prec_RR, int E_public);
int mbedtls_mpi_exp_mod_unsafe(mbedtls_mpi *X, const mbedtls_mpi *A,
const mbedtls_mpi *E, const mbedtls_mpi *N,
mbedtls_mpi *prec_RR);
/**
* \brief Perform a modular exponentiation: X = A^E mod N

31
tf-psa-crypto/drivers/builtin/src/bignum.c

@ -1610,9 +1610,13 @@ int mbedtls_mpi_mod_int(mbedtls_mpi_uint *r, const mbedtls_mpi *A, mbedtls_mpi_s
return 0;
}
int mbedtls_mpi_exp_mod_optionally_safe(mbedtls_mpi *X, const mbedtls_mpi *A,
const mbedtls_mpi *E, const mbedtls_mpi *N,
mbedtls_mpi *prec_RR, int E_public)
/*
* Warning! If the parameter E_public has MBEDTLS_MPI_IS_PUBLIC as its value,
* this function is not constant time with respect to the exponent (parameter E).
*/
static int mbedtls_mpi_exp_mod_optionally_safe(mbedtls_mpi *X, const mbedtls_mpi *A,
const mbedtls_mpi *E, const mbedtls_mpi *N,
mbedtls_mpi *prec_RR, int E_public)
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@ -1695,15 +1699,11 @@ int mbedtls_mpi_exp_mod_optionally_safe(mbedtls_mpi *X, const mbedtls_mpi *A,
{
mbedtls_mpi_uint mm = mbedtls_mpi_core_montmul_init(N->p);
mbedtls_mpi_core_to_mont_rep(X->p, X->p, N->p, N->n, mm, RR.p, T);
mbedtls_mpi_core_exp_mod_optionally_safe(X->p,
X->p,
N->p,
N->n,
E->p,
E->n,
RR.p,
T,
E_public);
if (E_public == MBEDTLS_MPI_IS_PUBLIC) {
mbedtls_mpi_core_exp_mod_unsafe(X->p, X->p, N->p, N->n, E->p, E->n, RR.p, T);
} else {
mbedtls_mpi_core_exp_mod(X->p, X->p, N->p, N->n, E->p, E->n, RR.p, T);
}
mbedtls_mpi_core_from_mont_rep(X->p, X->p, N->p, N->n, mm, T);
}
@ -1735,6 +1735,13 @@ int mbedtls_mpi_exp_mod(mbedtls_mpi *X, const mbedtls_mpi *A,
return mbedtls_mpi_exp_mod_optionally_safe(X, A, E, N, prec_RR, MBEDTLS_MPI_IS_SECRET);
}
int mbedtls_mpi_exp_mod_unsafe(mbedtls_mpi *X, const mbedtls_mpi *A,
const mbedtls_mpi *E, const mbedtls_mpi *N,
mbedtls_mpi *prec_RR)
{
return mbedtls_mpi_exp_mod_optionally_safe(X, A, E, N, prec_RR, MBEDTLS_MPI_IS_PUBLIC);
}
/*
* Greatest common divisor: G = gcd(A, B) (HAC 14.54)
*/

39
tf-psa-crypto/drivers/builtin/src/bignum_core.c

@ -748,6 +748,9 @@ static void exp_mod_precompute_window(const mbedtls_mpi_uint *A,
}
/* Exponentiation: X := A^E mod N.
*
* Warning! If the parameter E_public has MBEDTLS_MPI_IS_PUBLIC as its value,
* this function is not constant time with respect to the exponent (parameter E).
*
* A must already be in Montgomery form.
*
@ -759,15 +762,15 @@ static void exp_mod_precompute_window(const mbedtls_mpi_uint *A,
* (The difference is that the body in our loop processes a single bit instead
* of a full window.)
*/
void mbedtls_mpi_core_exp_mod_optionally_safe(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N,
size_t AN_limbs,
const mbedtls_mpi_uint *E,
size_t E_limbs,
const mbedtls_mpi_uint *RR,
mbedtls_mpi_uint *T,
int E_public)
static void mbedtls_mpi_core_exp_mod_optionally_safe(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N,
size_t AN_limbs,
const mbedtls_mpi_uint *E,
size_t E_limbs,
const mbedtls_mpi_uint *RR,
mbedtls_mpi_uint *T,
int E_public)
{
const size_t wsize = exp_mod_get_window_size(E_limbs * biL);
const size_t welem = ((size_t) 1) << wsize;
@ -873,6 +876,24 @@ void mbedtls_mpi_core_exp_mod(mbedtls_mpi_uint *X,
MBEDTLS_MPI_IS_SECRET);
}
void mbedtls_mpi_core_exp_mod_unsafe(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N, size_t AN_limbs,
const mbedtls_mpi_uint *E, size_t E_limbs,
const mbedtls_mpi_uint *RR,
mbedtls_mpi_uint *T)
{
mbedtls_mpi_core_exp_mod_optionally_safe(X,
A,
N,
AN_limbs,
E,
E_limbs,
RR,
T,
MBEDTLS_MPI_IS_PUBLIC);
}
mbedtls_mpi_uint mbedtls_mpi_core_sub_int(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
mbedtls_mpi_uint c, /* doubles as carry */

18
tf-psa-crypto/drivers/builtin/src/bignum_core.h

@ -618,6 +618,8 @@ size_t mbedtls_mpi_core_exp_mod_working_limbs(size_t AN_limbs, size_t E_limbs);
* \brief Perform a modular exponentiation with public or secret exponent:
* X = A^E mod N, where \p A is already in Montgomery form.
*
* \warning This function is not constant time with respect to \p E (the exponent).
*
* \p X may be aliased to \p A, but not to \p RR or \p E, even if \p E_limbs ==
* \p AN_limbs.
*
@ -640,17 +642,13 @@ size_t mbedtls_mpi_core_exp_mod_working_limbs(size_t AN_limbs, size_t E_limbs);
* It is up to the caller to zeroize \p T when it is no
* longer needed, and before freeing it if it was dynamically
* allocated.
* \param[in] E_public Set to MBEDTLS_MPI_IS_PUBLIC to gain some performance
* when the value of E is public.
* Set to MBEDTLS_MPI_IS_SECRET when the value of E is secret.
*/
void mbedtls_mpi_core_exp_mod_optionally_safe(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N, size_t AN_limbs,
const mbedtls_mpi_uint *E, size_t E_limbs,
const mbedtls_mpi_uint *RR,
mbedtls_mpi_uint *T,
int E_public);
void mbedtls_mpi_core_exp_mod_unsafe(mbedtls_mpi_uint *X,
const mbedtls_mpi_uint *A,
const mbedtls_mpi_uint *N, size_t AN_limbs,
const mbedtls_mpi_uint *E, size_t E_limbs,
const mbedtls_mpi_uint *RR,
mbedtls_mpi_uint *T);
/**
* \brief Perform a modular exponentiation with secret exponent: