From 12663092bc042d1c59ae0d4879167c47a9b2fc4f Mon Sep 17 00:00:00 2001 From: Neil Armstrong Date: Wed, 15 Jun 2022 16:00:00 +0200 Subject: [PATCH] Introduce mbedtls_ecjpake_write_shared_key() to export the EC J-PAKE shared key material before the KDF() Signed-off-by: Neil Armstrong --- include/mbedtls/ecjpake.h | 23 ++++++++++ library/ecjpake.c | 97 ++++++++++++++++++++++++++++++++------- 2 files changed, 104 insertions(+), 16 deletions(-) diff --git a/include/mbedtls/ecjpake.h b/include/mbedtls/ecjpake.h index ffdea05bcf..5b57455576 100644 --- a/include/mbedtls/ecjpake.h +++ b/include/mbedtls/ecjpake.h @@ -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. diff --git a/library/ecjpake.c b/library/ecjpake.c index 7447354bc5..17d04387d4 100644 --- a/library/ecjpake.c +++ b/library/ecjpake.c @@ -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 */