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Merge remote-tracking branch 'upstream-restricted/pr/556' into mbedtls-2.16-restricted

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This commit is contained in:
Gilles Peskine 2019-08-14 16:37:16 +02:00
parent 3a930650c8 7ffe827fca
commit 33f66ba6fd
5 changed files with 220 additions and 15 deletions
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10
ChangeLog
View file

@ -6,6 +6,16 @@ Security
* Fix a missing error detection in ECJPAKE. This could have caused a
predictable shared secret if a hardware accelerator failed and the other
side of the key exchange had a similar bug.
* The deterministic ECDSA calculation reused the scheme's HMAC-DRBG to
implement blinding. Because of this for the same key and message the same
blinding value was generated. This reduced the effectiveness of the
countermeasure and leaked information about the private key through side
channels. Reported by Jack Lloyd.
API Changes
* The new function mbedtls_ecdsa_sign_det_ext() is similar to
mbedtls_ecdsa_sign_det() but allows passing an external RNG for the
purpose of blinding.
Bugfix
* Fix to allow building test suites with any warning that detects unused

10
include/mbedtls/config.h
View file

@ -440,6 +440,16 @@
* dependencies on them, and considering stronger message digests
* and ciphers instead.
*
* \warning If both MBEDTLS_ECDSA_SIGN_ALT and MBEDTLS_ECDSA_DETERMINISTIC are
* enabled, then the deterministic ECDH signature functions pass the
* the static HMAC-DRBG as RNG to mbedtls_ecdsa_sign(). Therefore
* alternative implementations should use the RNG only for generating
* the ephemeral key and nothing else. If this is not possible, then
* MBEDTLS_ECDSA_DETERMINISTIC should be disabled and an alternative
* implementation should be provided for mbedtls_ecdsa_sign_det_ext()
* (and for mbedtls_ecdsa_sign_det() too if backward compatibility is
* desirable).
*
*/
//#define MBEDTLS_MD2_PROCESS_ALT
//#define MBEDTLS_MD4_PROCESS_ALT

59
include/mbedtls/ecdsa.h
View file

@ -175,6 +175,19 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
* (SECG): SEC1 Elliptic Curve Cryptography</em>, section
* 4.1.3, step 5.
*
* \warning Since the output of the internal RNG is always the same for
* the same key and message, this limits the efficiency of
* blinding and leaks information through side channels. For
* secure behavior use mbedtls_ecdsa_sign_det_ext() instead.
*
* (Optimally the blinding is a random value that is different
* on every execution. In this case the blinding is still
* random from the attackers perspective, but is the same on
* each execution. This means that this blinding does not
* prevent attackers from recovering secrets by combining
* several measurement traces, but may prevent some attacks
* that exploit relationships between secret data.)
*
* \see ecp.h
*
* \param grp The context for the elliptic curve to use.
@ -200,6 +213,52 @@ int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r,
mbedtls_mpi *s, const mbedtls_mpi *d,
const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg );
/**
* \brief This function computes the ECDSA signature of a
* previously-hashed message, deterministic version.
*
* For more information, see <em>RFC-6979: Deterministic
* Usage of the Digital Signature Algorithm (DSA) and Elliptic
* Curve Digital Signature Algorithm (ECDSA)</em>.
*
* \note If the bitlength of the message hash is larger than the
* bitlength of the group order, then the hash is truncated as
* defined in <em>Standards for Efficient Cryptography Group
* (SECG): SEC1 Elliptic Curve Cryptography</em>, section
* 4.1.3, step 5.
*
* \see ecp.h
*
* \param grp The context for the elliptic curve to use.
* This must be initialized and have group parameters
* set, for example through mbedtls_ecp_group_load().
* \param r The MPI context in which to store the first part
* the signature. This must be initialized.
* \param s The MPI context in which to store the second part
* the signature. This must be initialized.
* \param d The private signing key. This must be initialized
* and setup, for example through mbedtls_ecp_gen_privkey().
* \param buf The hashed content to be signed. This must be a readable
* buffer of length \p blen Bytes. It may be \c NULL if
* \p blen is zero.
* \param blen The length of \p buf in Bytes.
* \param md_alg The hash algorithm used to hash the original data.
* \param f_rng_blind The RNG function used for blinding. This must not be
* \c NULL.
* \param p_rng_blind The RNG context to be passed to \p f_rng. This may be
* \c NULL if \p f_rng doesn't need a context parameter.
*
* \return \c 0 on success.
* \return An \c MBEDTLS_ERR_ECP_XXX or \c MBEDTLS_MPI_XXX
* error code on failure.
*/
int mbedtls_ecdsa_sign_det_ext( mbedtls_ecp_group *grp, mbedtls_mpi *r,
mbedtls_mpi *s, const mbedtls_mpi *d,
const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg,
int (*f_rng_blind)(void *, unsigned char *,
size_t),
void *p_rng_blind );
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
/**

121
library/ecdsa.c
View file

@ -254,6 +254,8 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
mbedtls_mpi *r, mbedtls_mpi *s,
const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
int (*f_rng_blind)(void *, unsigned char *, size_t),
void *p_rng_blind,
mbedtls_ecdsa_restart_ctx *rs_ctx )
{
int ret, key_tries, sign_tries;
@ -323,7 +325,9 @@ static int ecdsa_sign_restartable( mbedtls_ecp_group *grp,
mul:
#endif
MBEDTLS_MPI_CHK( mbedtls_ecp_mul_restartable( grp, &R, pk, &grp->G,
f_rng, p_rng, ECDSA_RS_ECP ) );
f_rng_blind,
p_rng_blind,
ECDSA_RS_ECP ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( pr, &R.X, &grp->N ) );
}
while( mbedtls_mpi_cmp_int( pr, 0 ) == 0 );
@ -349,7 +353,8 @@ modn:
* Generate a random value to blind inv_mod in next step,
* avoiding a potential timing leak.
*/
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, &t, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_gen_privkey( grp, &t, f_rng_blind,
p_rng_blind ) );
/*
* Step 6: compute s = (e + r * d) / k = t (e + rd) / (kt) mod n
@ -392,8 +397,9 @@ int mbedtls_ecdsa_sign( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
ECDSA_VALIDATE_RET( f_rng != NULL );
ECDSA_VALIDATE_RET( buf != NULL || blen == 0 );
/* Use the same RNG for both blinding and ephemeral key generation */
return( ecdsa_sign_restartable( grp, r, s, d, buf, blen,
f_rng, p_rng, NULL ) );
f_rng, p_rng, f_rng, p_rng, NULL ) );
}
#endif /* !MBEDTLS_ECDSA_SIGN_ALT */
@ -405,6 +411,8 @@ static int ecdsa_sign_det_restartable( mbedtls_ecp_group *grp,
mbedtls_mpi *r, mbedtls_mpi *s,
const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg,
int (*f_rng_blind)(void *, unsigned char *, size_t),
void *p_rng_blind,
mbedtls_ecdsa_restart_ctx *rs_ctx )
{
int ret;
@ -451,8 +459,70 @@ sign:
ret = mbedtls_ecdsa_sign( grp, r, s, d, buf, blen,
mbedtls_hmac_drbg_random, p_rng );
#else
ret = ecdsa_sign_restartable( grp, r, s, d, buf, blen,
mbedtls_hmac_drbg_random, p_rng, rs_ctx );
if( f_rng_blind != NULL )
ret = ecdsa_sign_restartable( grp, r, s, d, buf, blen,
mbedtls_hmac_drbg_random, p_rng,
f_rng_blind, p_rng_blind, rs_ctx );
else
{
mbedtls_hmac_drbg_context *p_rng_blind_det;
#if !defined(MBEDTLS_ECP_RESTARTABLE)
/*
* To avoid reusing rng_ctx and risking incorrect behavior we seed a
* second HMAC-DRBG with the same seed. We also apply a label to avoid
* reusing the bits of the ephemeral key for blinding and eliminate the
* risk that they leak this way.
*/
const char* blind_label = "BLINDING CONTEXT";
mbedtls_hmac_drbg_context rng_ctx_blind;
mbedtls_hmac_drbg_init( &rng_ctx_blind );
p_rng_blind_det = &rng_ctx_blind;
mbedtls_hmac_drbg_seed_buf( p_rng_blind_det, md_info,
data, 2 * grp_len );
ret = mbedtls_hmac_drbg_update_ret( p_rng_blind_det,
(const unsigned char*) blind_label,
strlen( blind_label ) );
if( ret != 0 )
{
mbedtls_hmac_drbg_free( &rng_ctx_blind );
goto cleanup;
}
#else
/*
* In the case of restartable computations we would either need to store
* the second RNG in the restart context too or set it up at every
* restart. The first option would penalize the correct application of
* the function and the second would defeat the purpose of the
* restartable feature.
*
* Therefore in this case we reuse the original RNG. This comes with the
* price that the resulting signature might not be a valid deterministic
* ECDSA signature with a very low probability (same magnitude as
* successfully guessing the private key). However even then it is still
* a valid ECDSA signature.
*/
p_rng_blind_det = p_rng;
#endif /* MBEDTLS_ECP_RESTARTABLE */
/*
* Since the output of the RNGs is always the same for the same key and
* message, this limits the efficiency of blinding and leaks information
* through side channels. After mbedtls_ecdsa_sign_det() is removed NULL
* won't be a valid value for f_rng_blind anymore. Therefore it should
* be checked by the caller and this branch and check can be removed.
*/
ret = ecdsa_sign_restartable( grp, r, s, d, buf, blen,
mbedtls_hmac_drbg_random, p_rng,
mbedtls_hmac_drbg_random, p_rng_blind_det,
rs_ctx );
#if !defined(MBEDTLS_ECP_RESTARTABLE)
mbedtls_hmac_drbg_free( &rng_ctx_blind );
#endif
}
#endif /* MBEDTLS_ECDSA_SIGN_ALT */
cleanup:
@ -465,11 +535,12 @@ cleanup:
}
/*
* Deterministic signature wrapper
* Deterministic signature wrappers
*/
int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi *s,
const mbedtls_mpi *d, const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg )
int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r,
mbedtls_mpi *s, const mbedtls_mpi *d,
const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg )
{
ECDSA_VALIDATE_RET( grp != NULL );
ECDSA_VALIDATE_RET( r != NULL );
@ -477,7 +548,27 @@ int mbedtls_ecdsa_sign_det( mbedtls_ecp_group *grp, mbedtls_mpi *r, mbedtls_mpi
ECDSA_VALIDATE_RET( d != NULL );
ECDSA_VALIDATE_RET( buf != NULL || blen == 0 );
return( ecdsa_sign_det_restartable( grp, r, s, d, buf, blen, md_alg, NULL ) );
return( ecdsa_sign_det_restartable( grp, r, s, d, buf, blen, md_alg,
NULL, NULL, NULL ) );
}
int mbedtls_ecdsa_sign_det_ext( mbedtls_ecp_group *grp, mbedtls_mpi *r,
mbedtls_mpi *s, const mbedtls_mpi *d,
const unsigned char *buf, size_t blen,
mbedtls_md_type_t md_alg,
int (*f_rng_blind)(void *, unsigned char *,
size_t),
void *p_rng_blind )
{
ECDSA_VALIDATE_RET( grp != NULL );
ECDSA_VALIDATE_RET( r != NULL );
ECDSA_VALIDATE_RET( s != NULL );
ECDSA_VALIDATE_RET( d != NULL );
ECDSA_VALIDATE_RET( buf != NULL || blen == 0 );
ECDSA_VALIDATE_RET( f_rng_blind != NULL );
return( ecdsa_sign_det_restartable( grp, r, s, d, buf, blen, md_alg,
f_rng_blind, p_rng_blind, NULL ) );
}
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
@ -656,11 +747,9 @@ int mbedtls_ecdsa_write_signature_restartable( mbedtls_ecdsa_context *ctx,
mbedtls_mpi_init( &s );
#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
(void) f_rng;
(void) p_rng;
MBEDTLS_MPI_CHK( ecdsa_sign_det_restartable( &ctx->grp, &r, &s, &ctx->d,
hash, hlen, md_alg, rs_ctx ) );
hash, hlen, md_alg, f_rng,
p_rng, rs_ctx ) );
#else
(void) md_alg;
@ -668,8 +757,10 @@ int mbedtls_ecdsa_write_signature_restartable( mbedtls_ecdsa_context *ctx,
MBEDTLS_MPI_CHK( mbedtls_ecdsa_sign( &ctx->grp, &r, &s, &ctx->d,
hash, hlen, f_rng, p_rng ) );
#else
/* Use the same RNG for both blinding and ephemeral key generation */
MBEDTLS_MPI_CHK( ecdsa_sign_restartable( &ctx->grp, &r, &s, &ctx->d,
hash, hlen, f_rng, p_rng, rs_ctx ) );
hash, hlen, f_rng, p_rng, f_rng,
p_rng, rs_ctx ) );
#endif /* MBEDTLS_ECDSA_SIGN_ALT */
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */

35
tests/suites/test_suite_ecdsa.function
View file

@ -74,6 +74,31 @@ void ecdsa_invalid_param( )
mbedtls_ecdsa_sign_det( &grp, &m, &m, &m,
NULL, sizeof( buf ),
valid_md ) );
TEST_INVALID_PARAM_RET( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
mbedtls_ecdsa_sign_det_ext( NULL, &m, &m, &m,
buf, sizeof( buf ),
valid_md,
rnd_std_rand, NULL ) );
TEST_INVALID_PARAM_RET( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
mbedtls_ecdsa_sign_det_ext( &grp, NULL, &m, &m,
buf, sizeof( buf ),
valid_md,
rnd_std_rand, NULL ) );
TEST_INVALID_PARAM_RET( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
mbedtls_ecdsa_sign_det_ext( &grp, &m, NULL, &m,
buf, sizeof( buf ),
valid_md,
rnd_std_rand, NULL ) );
TEST_INVALID_PARAM_RET( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
mbedtls_ecdsa_sign_det_ext( &grp, &m, &m, NULL,
buf, sizeof( buf ),
valid_md,
rnd_std_rand, NULL ) );
TEST_INVALID_PARAM_RET( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
mbedtls_ecdsa_sign_det_ext( &grp, &m, &m, &m,
NULL, sizeof( buf ),
valid_md,
rnd_std_rand, NULL ) );
#endif /* MBEDTLS_ECDSA_DETERMINISTIC */
TEST_INVALID_PARAM_RET( MBEDTLS_ERR_ECP_BAD_INPUT_DATA,
@ -330,6 +355,16 @@ void ecdsa_det_test_vectors( int id, char * d_str, int md_alg, char * msg,
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &r, &r_check ) == 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &s, &s_check ) == 0 );
mbedtls_mpi_free( &r ); mbedtls_mpi_free( &s );
mbedtls_mpi_init( &r ); mbedtls_mpi_init( &s );
TEST_ASSERT(
mbedtls_ecdsa_sign_det_ext( &grp, &r, &s, &d, hash, hlen,
md_alg, rnd_std_rand, NULL )
== 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &r, &r_check ) == 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &s, &s_check ) == 0 );
exit:
mbedtls_ecp_group_free( &grp );
mbedtls_mpi_free( &d ); mbedtls_mpi_free( &r ); mbedtls_mpi_free( &s );