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Introduce mbedtls_ecjpake_write_shared_key() to export the EC J-PAKE shared key material before the KDF()

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Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
This commit is contained in:
Neil Armstrong 2022-06-15 16:00:00 +02:00
parent 75673abef5
commit 12663092bc
2 changed files with 104 additions and 16 deletions
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23
include/mbedtls/ecjpake.h
View file

@ -258,6 +258,29 @@ int mbedtls_ecjpake_derive_secret( mbedtls_ecjpake_context *ctx,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
/**
* \brief Write the shared key material to be passed to a Key
* Derivation Function as described in RFC8236.
*
* \param ctx The ECJPAKE context to use. This must be initialized,
* set up and have performed both round one and two.
* \param buf The buffer to write the derived secret to. This must
* be a writable buffer of length \p len Bytes.
* \param len The length of \p buf in Bytes.
* \param olen The address at which to store the total number of Bytes
* written to \p buf. This must not be \c NULL.
* \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. This
* may be \c NULL if \p f_rng doesn't use a context.
*
* \return \c 0 if successful.
* \return A negative error code on failure.
*/
int mbedtls_ecjpake_write_shared_key( mbedtls_ecjpake_context *ctx,
unsigned char *buf, size_t len, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng );
/**
* \brief This clears an ECJPAKE context and frees any
* embedded data structure.

97
library/ecjpake.c
View file

@ -760,22 +760,14 @@ cleanup:
/*
* Derive PMS (7.4.2.7 / 7.4.2.8)
*/
int mbedtls_ecjpake_derive_secret( mbedtls_ecjpake_context *ctx,
unsigned char *buf, size_t len, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
static int mbedtls_ecjpake_derive_k( mbedtls_ecjpake_context *ctx,
mbedtls_ecp_point *K,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_ecp_point K;
mbedtls_mpi m_xm2_s, one;
unsigned char kx[MBEDTLS_ECP_MAX_BYTES];
size_t x_bytes;
*olen = mbedtls_hash_info_get_size( ctx->md_type );
if( len < *olen )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
mbedtls_ecp_point_init( &K );
mbedtls_mpi_init( &m_xm2_s );
mbedtls_mpi_init( &one );
@ -788,12 +780,39 @@ int mbedtls_ecjpake_derive_secret( mbedtls_ecjpake_context *ctx,
*/
MBEDTLS_MPI_CHK( ecjpake_mul_secret( &m_xm2_s, -1, &ctx->xm2, &ctx->s,
&ctx->grp.N, f_rng, p_rng ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( &ctx->grp, &K,
MBEDTLS_MPI_CHK( mbedtls_ecp_muladd( &ctx->grp, K,
&one, &ctx->Xp,
&m_xm2_s, &ctx->Xp2 ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, &K, &ctx->xm2, &K,
MBEDTLS_MPI_CHK( mbedtls_ecp_mul( &ctx->grp, K, &ctx->xm2, K,
f_rng, p_rng ) );
cleanup:
mbedtls_mpi_free( &m_xm2_s );
mbedtls_mpi_free( &one );
return( ret );
}
int mbedtls_ecjpake_derive_secret( mbedtls_ecjpake_context *ctx,
unsigned char *buf, size_t len, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_ecp_point K;
unsigned char kx[MBEDTLS_ECP_MAX_BYTES];
size_t x_bytes;
*olen = mbedtls_hash_info_get_size( ctx->md_type );
if( len < *olen )
return( MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL );
mbedtls_ecp_point_init( &K );
ret = mbedtls_ecjpake_derive_k(ctx, &K, f_rng, p_rng);
if( ret )
goto cleanup;
/* PMS = SHA-256( K.X ) */
x_bytes = ( ctx->grp.pbits + 7 ) / 8;
MBEDTLS_MPI_CHK( mbedtls_mpi_write_binary( &K.X, kx, x_bytes ) );
@ -802,8 +821,31 @@ int mbedtls_ecjpake_derive_secret( mbedtls_ecjpake_context *ctx,
cleanup:
mbedtls_ecp_point_free( &K );
mbedtls_mpi_free( &m_xm2_s );
mbedtls_mpi_free( &one );
return( ret );
}
int mbedtls_ecjpake_write_shared_key( mbedtls_ecjpake_context *ctx,
unsigned char *buf, size_t len, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
mbedtls_ecp_point K;
mbedtls_ecp_point_init( &K );
ret = mbedtls_ecjpake_derive_k(ctx, &K, f_rng, p_rng);
if( ret )
goto cleanup;
ret = mbedtls_ecp_point_write_binary( &ctx->grp, &K, ctx->point_format,
olen, buf, len );
if( ret != 0 )
goto cleanup;
cleanup:
mbedtls_ecp_point_free( &K );
return( ret );
}
@ -958,6 +1000,15 @@ static const unsigned char ecjpake_test_cli_two[] = {
0xcc, 0x38, 0xdb, 0xdc, 0xae, 0x60, 0xd9, 0xc5, 0x4c
};
static const unsigned char ecjpake_test_shared_key[] = {
0x04, 0x01, 0xab, 0xe9, 0xf2, 0xc7, 0x3a, 0x99, 0x14, 0xcb, 0x1f, 0x80,
0xfb, 0x9d, 0xdb, 0x7e, 0x00, 0x12, 0xa8, 0x9c, 0x2f, 0x39, 0x27, 0x79,
0xf9, 0x64, 0x40, 0x14, 0x75, 0xea, 0xc1, 0x31, 0x28, 0x43, 0x8f, 0xe1,
0x12, 0x41, 0xd6, 0xc1, 0xe5, 0x5f, 0x7b, 0x80, 0x88, 0x94, 0xc9, 0xc0,
0x27, 0xa3, 0x34, 0x41, 0xf5, 0xcb, 0xa1, 0xfe, 0x6c, 0xc7, 0xe6, 0x12,
0x17, 0xc3, 0xde, 0x27, 0xb4,
};
static const unsigned char ecjpake_test_pms[] = {
0xf3, 0xd4, 0x7f, 0x59, 0x98, 0x44, 0xdb, 0x92, 0xa5, 0x69, 0xbb, 0xe7,
0x98, 0x1e, 0x39, 0xd9, 0x31, 0xfd, 0x74, 0x3b, 0xf2, 0x2e, 0x98, 0xf9,
@ -1144,6 +1195,13 @@ int mbedtls_ecjpake_self_test( int verbose )
TEST_ASSERT( len == sizeof( ecjpake_test_pms ) );
TEST_ASSERT( memcmp( buf, ecjpake_test_pms, len ) == 0 );
/* Server derives K as unsigned binary data */
TEST_ASSERT( mbedtls_ecjpake_write_shared_key( &srv,
buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );
TEST_ASSERT( len == sizeof( ecjpake_test_shared_key ) );
TEST_ASSERT( memcmp( buf, ecjpake_test_shared_key, len ) == 0 );
memset( buf, 0, len ); /* Avoid interferences with next step */
/* Client derives PMS */
@ -1153,6 +1211,13 @@ int mbedtls_ecjpake_self_test( int verbose )
TEST_ASSERT( len == sizeof( ecjpake_test_pms ) );
TEST_ASSERT( memcmp( buf, ecjpake_test_pms, len ) == 0 );
/* Client derives K as unsigned binary data */
TEST_ASSERT( mbedtls_ecjpake_write_shared_key( &cli,
buf, sizeof( buf ), &len, ecjpake_lgc, NULL ) == 0 );
TEST_ASSERT( len == sizeof( ecjpake_test_shared_key ) );
TEST_ASSERT( memcmp( buf, ecjpake_test_shared_key, len ) == 0 );
if( verbose != 0 )
mbedtls_printf( "passed\n" );
#endif /* ! MBEDTLS_ECJPAKE_ALT */