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mbedtls_ecp_gen_privkey_sw: generalize to mbedtls_mpi_random

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Rename mbedtls_ecp_gen_privkey_sw to mbedtls_mpi_random since it has
no particular connection to elliptic curves beyond the fact that its
operation is defined by the deterministic ECDSA specification. This is
a generic function that generates a random MPI between 1 inclusive and
N exclusive.

Slightly generalize the function to accept a different lower bound,
which adds a negligible amount of complexity.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-03-29 21:53:58 +02:00
parent 7888073147
commit 8cfffb30b3
4 changed files with 119 additions and 99 deletions
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23
library/ecp.c
View file

@ -3093,15 +3093,17 @@ cleanup:
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
MBEDTLS_STATIC_TESTABLE
int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
mbedtls_mpi *d,
int mbedtls_mpi_random( mbedtls_mpi *X,
mbedtls_mpi_sint min,
const mbedtls_mpi *N,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
/* SEC1 3.2.1: Generate d such that 1 <= n < N */
int ret = MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
/* SEC1 3.2.1: Generate X such that 1 <= n < N */
int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
int count = 0;
unsigned cmp = 0;
size_t n_bits = mbedtls_mpi_bitlen( N );
size_t n_bytes = ( n_bits + 7 ) / 8;
/*
@ -3114,8 +3116,8 @@ int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
*/
do
{
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( d, n_bytes, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( d, 8 * n_bytes - n_bits ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_fill_random( X, n_bytes, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( X, 8 * n_bytes - n_bits ) );
/*
* Each try has at worst a probability 1/2 of failing (the msb has
@ -3128,17 +3130,17 @@ int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
*/
if( ++count > 30 )
{
ret = MBEDTLS_ERR_ECP_RANDOM_FAILED;
ret = MBEDTLS_ERR_MPI_NOT_ACCEPTABLE;
goto cleanup;
}
ret = mbedtls_mpi_lt_mpi_ct( d, N, &cmp );
ret = mbedtls_mpi_lt_mpi_ct( X, N, &cmp );
if( ret != 0 )
{
goto cleanup;
}
}
while( mbedtls_mpi_cmp_int( d, 1 ) < 0 || cmp != 1 );
while( mbedtls_mpi_cmp_int( X, min ) < 0 || cmp != 1 );
cleanup:
return( ret );
@ -3164,8 +3166,7 @@ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
if( mbedtls_ecp_get_type( grp ) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS )
return( mbedtls_ecp_gen_privkey_sw( &grp->N, grp->nbits, d,
f_rng, p_rng ) );
return( mbedtls_mpi_random( d, 1, &grp->N, f_rng, p_rng ) );
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
return( MBEDTLS_ERR_ECP_BAD_INPUT_DATA );

35
library/ecp_invasive.h
View file

@ -77,23 +77,34 @@ int mbedtls_ecp_gen_privkey_mx( size_t n_bits,
#endif /* MBEDTLS_ECP_MONTGOMERY_ENABLED */
#if defined(MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED)
/** Generate a private key on a short Weierstrass curve.
/** Generate a random number uniformly in a range.
*
* This function generates a random number between \p min inclusive and
* \p N exclusive.
*
* The procedure complies with RFC 6979 §3.3 (deterministic ECDSA)
* when the RNG is a suitably parametrized instance of HMAC_DRBG.
* when the RNG is a suitably parametrized instance of HMAC_DRBG
* and \p min is \c 1.
*
* \p N The upper bound of the range.
* \p n_bits The size of \p N in bits. This value must be correct,
* otherwise the result is unpredictable.
* \param d A random number, uniformly generated in the range [1, N-1].
* \param f_rng The RNG function.
* \param p_rng The RNG context to be passed to \p f_rng.
* \note There are `N - min` possible outputs. The lower bound
* \p min can be reached, but the upper bound \p N cannot.
*
* \return \c 0 on success.
* \return \c MBEDTLS_ERR_ECP_xxx or MBEDTLS_ERR_MPI_xxx on failure.
* \param X The destination MPI. This must point to an initialized MPI.
* \param min The minimum value to return.
* It must be nonnegative.
* \param N The upper bound of the range, exclusive.
* In other words, this is one plus the maximum value to return.
* \p N must be strictly larger than \p min.
* \param f_rng The RNG function to use. This must not be \c NULL.
* \param p_rng The RNG parameter to be passed to \p f_rng.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
* \return Another negative error code on failure.
*/
int mbedtls_ecp_gen_privkey_sw( const mbedtls_mpi *N, size_t n_bits,
mbedtls_mpi *d,
int mbedtls_mpi_random( mbedtls_mpi *X,
mbedtls_mpi_sint min,
const mbedtls_mpi *N,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
#endif /* MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */

129
tests/suites/test_suite_ecp.data
View file

@ -312,95 +312,104 @@ genkey_mx_known_answer:447:"ffffffffffffffffffffffffffffffffffffffffffffffffffff
ECP generate Montgomery key: Curve448, not enough entropy
genkey_mx_known_answer:447:"4f0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f30313233343536":""
ECP generate in range: 4
genkey_sw_many:"04":1000
MPI random in range: 1..4
mpi_random_many:1:"04":1000
ECP generate in range: 5
genkey_sw_many:"05":1000
MPI random in range: 1..5
mpi_random_many:1:"05":1000
ECP generate in range: 6
genkey_sw_many:"06":1000
MPI random in range: 1..6
mpi_random_many:1:"06":1000
ECP generate in range: 7
genkey_sw_many:"07":1000
MPI random in range: 1..7
mpi_random_many:1:"07":1000
ECP generate in range: 8
genkey_sw_many:"08":1000
MPI random in range: 1..8
mpi_random_many:1:"08":1000
ECP generate in range: 9
genkey_sw_many:"09":1000
MPI random in range: 1..9
mpi_random_many:1:"09":1000
ECP generate in range: 10
genkey_sw_many:"0a":1000
MPI random in range: 1..10
mpi_random_many:1:"0a":1000
ECP generate in range: 11
genkey_sw_many:"0b":1000
MPI random in range: 1..11
mpi_random_many:1:"0b":1000
ECP generate in range: 12
genkey_sw_many:"0c":1000
MPI random in range: 1..12
mpi_random_many:1:"0c":1000
ECP generate in range: 255
genkey_sw_many:"ff":100
MPI random in range: 1..255
mpi_random_many:1:"ff":100
ECP generate in range: 256
genkey_sw_many:"0100":100
MPI random in range: 1..256
mpi_random_many:1:"0100":100
ECP generate in range: 257
genkey_sw_many:"0101":100
MPI random in range: 1..257
mpi_random_many:1:"0101":100
ECP generate in range: 272
genkey_sw_many:"0110":100
MPI random in range: 1..272
mpi_random_many:1:"0110":100
ECP generate in range: 2^64-1
genkey_sw_many:"ffffffffffffffff":100
MPI random in range: 1..2^64-1
mpi_random_many:1:"ffffffffffffffff":100
ECP generate in range: 2^64
genkey_sw_many:"010000000000000000":100
MPI random in range: 1..2^64
mpi_random_many:1:"010000000000000000":100
ECP generate in range: 2^64+1
genkey_sw_many:"010000000000000001":100
MPI random in range: 1..2^64+1
mpi_random_many:1:"010000000000000001":100
ECP generate in range: 2^64+2^63
genkey_sw_many:"018000000000000000":100
MPI random in range: 1..2^64+2^63
mpi_random_many:1:"018000000000000000":100
ECP generate in range: 2^65-1
genkey_sw_many:"01ffffffffffffffff":100
MPI random in range: 1..2^65-1
mpi_random_many:1:"01ffffffffffffffff":100
ECP generate in range: 2^65
genkey_sw_many:"020000000000000000":100
MPI random in range: 1..2^65
mpi_random_many:1:"020000000000000000":100
ECP generate in range: 2^65+1
genkey_sw_many:"020000000000000001":100
MPI random in range: 1..2^65+1
mpi_random_many:1:"020000000000000001":100
ECP generate in range: 2^65+2^64
genkey_sw_many:"030000000000000000":100
MPI random in range: 1..2^65+2^64
mpi_random_many:1:"030000000000000000":100
ECP generate in range: 2^66+2^65
genkey_sw_many:"060000000000000000":100
MPI random in range: 1..2^66+2^65
mpi_random_many:1:"060000000000000000":100
ECP generate in range: 2^71-1
genkey_sw_many:"7fffffffffffffffff":100
MPI random in range: 1..2^71-1
mpi_random_many:1:"7fffffffffffffffff":100
ECP generate in range: 2^71
genkey_sw_many:"800000000000000000":100
MPI random in range: 1..2^71
mpi_random_many:1:"800000000000000000":100
ECP generate in range: 2^71+1
genkey_sw_many:"800000000000000001":100
MPI random in range: 1..2^71+1
mpi_random_many:1:"800000000000000001":100
ECP generate in range: 2^71+2^63
genkey_sw_many:"c00000000000000000":100
MPI random in range: 1..2^71+2^63
mpi_random_many:1:"c00000000000000000":100
ECP generate in range: 2^72-1
genkey_sw_many:"ffffffffffffffffff":100
MPI random in range: 1..2^72-1
mpi_random_many:1:"ffffffffffffffffff":100
ECP generate in range: 2^72
genkey_sw_many:"01000000000000000000":100
MPI random in range: 1..2^72
mpi_random_many:1:"01000000000000000000":100
ECP generate in range: 2^72+1
genkey_sw_many:"01000000000000000001":100
MPI random in range: 1..2^72+1
mpi_random_many:1:"01000000000000000001":100
ECP generate in range: 2^72+2^63
genkey_sw_many:"01800000000000000000":100
MPI random in range: 1..2^72+2^63
mpi_random_many:1:"01800000000000000000":100
MPI random in range: 0..4
mpi_random_many:0:"04":1000
MPI random in range: 2..4
mpi_random_many:1:"04":1000
MPI random in range: 3..4
mpi_random_many:1:"04":1000
ECP read key #1 (short weierstrass, too small)
depends_on:MBEDTLS_ECP_DP_SECP192R1_ENABLED

21
tests/suites/test_suite_ecp.function
View file

@ -1324,7 +1324,7 @@ exit:
/* END_CASE */
/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS:MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
void genkey_sw_many( data_t *bound_bytes, int iterations )
void mpi_random_many( int min, data_t *bound_bytes, int iterations )
{
/* Generate numbers in the range 1..bound-1. Do it iterations times.
* This function assumes that the value of bound is at least 2 and
@ -1332,11 +1332,11 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
* effectively never occurs.
*/
mbedtls_mpi bound;
mbedtls_mpi upper_bound;
size_t n_bits;
mbedtls_mpi result;
size_t b;
/* If bound is small, stats[b] is the number of times the value b
/* If upper_bound is small, stats[b] is the number of times the value b
* has been generated. Otherwise stats[b] is the number of times a
* value with bit b set has been generated. */
size_t *stats = NULL;
@ -1344,12 +1344,12 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
int full_stats;
size_t i;
mbedtls_mpi_init( &bound );
mbedtls_mpi_init( &upper_bound );
mbedtls_mpi_init( &result );
TEST_EQUAL( 0, mbedtls_mpi_read_binary( &bound,
TEST_EQUAL( 0, mbedtls_mpi_read_binary( &upper_bound,
bound_bytes->x, bound_bytes->len ) );
n_bits = mbedtls_mpi_bitlen( &bound );
n_bits = mbedtls_mpi_bitlen( &upper_bound );
/* Consider a bound "small" if it's less than 2^5. This value is chosen
* to be small enough that the probability of missing one value is
* negligible given the number of iterations. It must be less than
@ -1370,12 +1370,11 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
for( i = 0; i < (size_t) iterations; i++ )
{
mbedtls_test_set_step( i );
TEST_EQUAL( 0, mbedtls_ecp_gen_privkey_sw(
&bound, n_bits, &result,
TEST_EQUAL( 0, mbedtls_mpi_random( &result, min, &upper_bound,
mbedtls_test_rnd_std_rand, NULL ) );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &result, &bound ) < 0 );
TEST_ASSERT( mbedtls_mpi_cmp_int( &result, 1 ) >= 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &result, &upper_bound ) < 0 );
TEST_ASSERT( mbedtls_mpi_cmp_int( &result, min ) >= 0 );
if( full_stats )
{
uint8_t value;
@ -1425,7 +1424,7 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
}
exit:
mbedtls_mpi_free( &bound );
mbedtls_mpi_free( &upper_bound );
mbedtls_mpi_free( &result );
mbedtls_free( stats );
}