From 72177e362b4298bf9349861c430dd6d44c1a5ebb Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?= Date: Tue, 16 Jun 2020 12:51:42 +0200 Subject: [PATCH] Add fall-back to hash-based KDF for internal ECP DRBG MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The dependency on a DRBG module was perhaps a bit strict for LTS branches, so let's have an option that works with no DRBG when at least one SHA module is present. This changes the internal API of ecp_drbg_seed() by adding the size of the MPI as a parameter. Re-computing the size from the number of limbs doesn't work too well here as we're writing out to a fixed-size buffer and for some curves (P-521) that would round up too much. Using mbedtls_mpi_get_len() is not entirely satisfactory either as it would mean using a variable-length encoding, with could open side channels. Signed-off-by: Manuel Pégourié-Gonnard --- include/mbedtls/check_config.h | 5 +- library/ecp.c | 224 +++++++++++++++++++++++++++++++-- tests/scripts/all.sh | 63 ++++++++++ 3 files changed, 281 insertions(+), 11 deletions(-) diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h index 0aef0d068..3ae86a19b 100644 --- a/include/mbedtls/check_config.h +++ b/include/mbedtls/check_config.h @@ -144,8 +144,11 @@ defined(MBEDTLS_ECP_ALT) || \ defined(MBEDTLS_CTR_DRBG_C) || \ defined(MBEDTLS_HMAC_DRBG_C) || \ + defined(MBEDTLS_SHA512_C) || \ + defined(MBEDTLS_SHA256_C) || \ + defined(MBEDTLS_SHA1_C) || \ defined(MBEDTLS_ECP_NO_INTERNAL_RNG)) -#error "MBEDTLS_ECP_C requires a DRBG module unless MBEDTLS_ECP_NO_INTERNAL_RNG is defined or an alternative implementation is used" +#error "MBEDTLS_ECP_C requires a DRBG or SHA module unless MBEDTLS_ECP_NO_INTERNAL_RNG is defined or an alternative implementation is used" #endif #if defined(MBEDTLS_PK_PARSE_C) && !defined(MBEDTLS_ASN1_PARSE_C) diff --git a/library/ecp.c b/library/ecp.c index 82c931f5e..b8ad9357a 100644 --- a/library/ecp.c +++ b/library/ecp.c @@ -109,6 +109,12 @@ #include "mbedtls/hmac_drbg.h" #elif defined(MBEDTLS_CTR_DRBG_C) #include "mbedtls/ctr_drbg.h" +#elif defined(MBEDTLS_SHA512_C) +#include "mbedtls/sha512.h" +#elif defined(MBEDTLS_SHA256_C) +#include "mbedtls/sha256.h" +#elif defined(MBEDTLS_SHA1_C) +#include "mbedtls/sha1.h" #else #error "Invalid configuration detected. Include check_config.h to ensure that the configuration is valid." #endif @@ -171,16 +177,16 @@ static inline int ecp_drbg_random( void *p_rng, } /* DRBG context seeding */ -static int ecp_drbg_seed( ecp_drbg_context *ctx, const mbedtls_mpi *secret ) +static int ecp_drbg_seed( ecp_drbg_context *ctx, + const mbedtls_mpi *secret, size_t secret_len ) { const unsigned char *secret_p = (const unsigned char *) secret->p; - const size_t secret_size = secret->n * sizeof( mbedtls_mpi_uint ); /* The list starts with strong hashes */ const mbedtls_md_type_t md_type = mbedtls_md_list()[0]; const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type( md_type ); - return( mbedtls_hmac_drbg_seed_buf( ctx, md_info, secret_p, secret_size ) ); + return( mbedtls_hmac_drbg_seed_buf( ctx, md_info, secret_p, secret_len ) ); } #elif defined(MBEDTLS_CTR_DRBG_C) @@ -222,18 +228,113 @@ static int ecp_ctr_drbg_null_entropy(void *ctx, unsigned char *out, size_t len) } /* DRBG context seeding */ -static int ecp_drbg_seed( ecp_drbg_context *ctx, const mbedtls_mpi *secret ) +static int ecp_drbg_seed( ecp_drbg_context *ctx, + const mbedtls_mpi *secret, size_t secret_len ) { const unsigned char *secret_p = (const unsigned char *) secret->p; - const size_t secret_size = secret->n * sizeof( mbedtls_mpi_uint ); return( mbedtls_ctr_drbg_seed( ctx, ecp_ctr_drbg_null_entropy, NULL, - secret_p, secret_size ) ); + secret_p, secret_len ) ); } -#else +#elif defined(MBEDTLS_SHA512_C) || \ + defined(MBEDTLS_SHA256_C) || \ + defined(MBEDTLS_SHA1_C) + +/* This will be used in the self-test function */ +#define ECP_ONE_STEP_KDF + +/* + * We need to expand secret data (the scalar) into a longer stream of bytes. + * + * We'll use the One-Step KDF from NIST SP 800-56C, with option 1 (H is a hash + * function) and empty FixedInfo. (Though we'll make it fit the DRBG API for + * convenience, this is not a full-fledged DRBG, but we don't need one here.) + * + * We need a basic hash abstraction layer to use whatever SHA is available. + */ +#if defined(MBEDTLS_SHA512_C) + +#define HASH_FUNC( in, ilen, out ) mbedtls_sha512_ret( in, ilen, out, 0 ); +#define HASH_BLOCK_BYTES ( 512 / 8 ) + +#elif defined(MBEDTLS_SHA256_C) + +#define HASH_FUNC( in, ilen, out ) mbedtls_sha256_ret( in, ilen, out, 0 ); +#define HASH_BLOCK_BYTES ( 256 / 8 ) + +#else // from a previous #if we know that SHA-1 is available if SHA-2 isn't + +#define HASH_FUNC mbedtls_sha1_ret +#define HASH_BLOCK_BYTES ( 160 / 8 ) + +#endif /* SHA512/SHA256/SHA1 abstraction */ + +/* + * State consists of a 32-bit counter plus the secret value. + * + * We stored them concatenated in a single buffer as that's what will get + * passed to the hash function. + */ +typedef struct { + size_t total_len; + uint8_t buf[4 + MBEDTLS_ECP_MAX_BYTES]; +} ecp_drbg_context; + +static void ecp_drbg_init( ecp_drbg_context *ctx ) +{ + memset( ctx, 0, sizeof( ecp_drbg_context ) ); +} + +static void ecp_drbg_free( ecp_drbg_context *ctx ) +{ + mbedtls_platform_zeroize( ctx, sizeof( ecp_drbg_context ) ); +} + +static int ecp_drbg_seed( ecp_drbg_context *ctx, + const mbedtls_mpi *secret, size_t secret_len ) +{ + ctx->total_len = 4 + secret_len; + memset( ctx->buf, 0, 4); + return( mbedtls_mpi_write_binary( secret, ctx->buf + 4, secret_len ) ); +} + +static int ecp_drbg_random( void *p_rng, unsigned char *output, size_t output_len ) +{ + ecp_drbg_context *ctx = p_rng; + int ret; + size_t len_done = 0; + + while( len_done < output_len ) + { + uint8_t tmp[HASH_BLOCK_BYTES]; + uint8_t use_len; + + /* We don't need to draw more that 255 blocks, so don't bother with + * carry propagation and just return an error instead. */ + ctx->buf[3] += 1; + if( ctx->buf[3] == 0 ) + return( MBEDTLS_ERR_ECP_RANDOM_FAILED ); + + ret = HASH_FUNC( ctx->buf, ctx->total_len, tmp ); + if( ret != 0 ) + return( ret ); + + if( output_len - len_done > HASH_BLOCK_BYTES ) + use_len = HASH_BLOCK_BYTES; + else + use_len = output_len - len_done; + + memcpy( output + len_done, tmp, use_len ); + len_done += use_len; + } + + return( 0 ); +} + +#else /* DRBG/SHA modules */ #error "Invalid configuration detected. Include check_config.h to ensure that the configuration is valid." -#endif /* DRBG modules */ +#endif /* DRBG/SHA modules */ #endif /* MBEDTLS_ECP_NO_INTERNAL_RNG */ #if defined(MBEDTLS_ECP_RESTARTABLE) @@ -2187,7 +2288,8 @@ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, rs_ctx->rsm->drbg_seeded == 0 ) #endif { - MBEDTLS_MPI_CHK( ecp_drbg_seed( p_rng, m ) ); + const size_t m_len = ( grp->nbits + 7 ) / 8; + MBEDTLS_MPI_CHK( ecp_drbg_seed( p_rng, m, m_len ) ); } #if defined(MBEDTLS_ECP_RESTARTABLE) if( rs_ctx != NULL && rs_ctx->rsm != NULL ) @@ -2471,7 +2573,8 @@ static int ecp_mul_mxz( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, #if !defined(MBEDTLS_ECP_NO_INTERNAL_RNG) if( f_rng == NULL ) { - MBEDTLS_MPI_CHK( ecp_drbg_seed( &drbg_ctx, m ) ); + const size_t m_len = ( grp->nbits + 7 ) / 8; + MBEDTLS_MPI_CHK( ecp_drbg_seed( &drbg_ctx, m, m_len ) ); f_rng = &ecp_drbg_random; p_rng = &drbg_ctx; } @@ -3091,6 +3194,89 @@ cleanup: #if defined(MBEDTLS_SELF_TEST) +#if defined(ECP_ONE_STEP_KDF) +/* + * There are no test vectors from NIST for the One-Step KDF in SP 800-56C, + * but unofficial ones can be found at: + * https://github.com/patrickfav/singlestep-kdf/wiki/NIST-SP-800-56C-Rev1:-Non-Official-Test-Vectors + * + * We only use the ones with empty fixedInfo, and for brevity's sake, only + * 32-bytes output (with SHA-1 that's more than one block, with SHA-256 + * exactly one block, and with SHA-512 less than one block). + */ +#if defined(MBEDTLS_SHA512_C) + +static const uint8_t test_kdf_z[16] = { + 0xeb, 0xf3, 0x19, 0x67, 0x1e, 0xac, 0xcc, 0x6f, + 0xc5, 0xc0, 0x5d, 0x95, 0x8d, 0x17, 0x15, 0x94, +}; +static const uint8_t test_kdf_out[32] = { + 0xa9, 0x48, 0x85, 0x67, 0x54, 0x7c, 0x2a, 0x8e, + 0x9e, 0xd1, 0x67, 0x76, 0xe3, 0x1c, 0x03, 0x92, + 0x41, 0x77, 0x2a, 0x9e, 0xc7, 0xcc, 0xd7, 0x1f, + 0xda, 0x12, 0xe9, 0xba, 0xc9, 0xb2, 0x17, 0x24, +}; + +#elif defined(MBEDTLS_SHA256_C) + +static const uint8_t test_kdf_z[16] = { + 0x0d, 0x5e, 0xc8, 0x9a, 0x68, 0xb1, 0xa7, 0xa0, + 0xdf, 0x95, 0x24, 0x54, 0x3f, 0x4d, 0x70, 0xef, +}; +static const uint8_t test_kdf_out[32] = { + 0x77, 0xbc, 0x94, 0x9e, 0xa0, 0xd3, 0xdd, 0x5c, + 0x8e, 0xb7, 0xeb, 0x84, 0x05, 0x40, 0x60, 0xfa, + 0x96, 0x6e, 0x7e, 0xcd, 0x73, 0x9f, 0xa1, 0xe6, + 0x34, 0x3f, 0x6d, 0x82, 0x16, 0x22, 0xb4, 0x45, +}; + +#elif defined(MBEDTLS_SHA1_C) + +static const uint8_t test_kdf_z[16] = { + 0x4e, 0x1e, 0x70, 0xc9, 0x88, 0x68, 0x19, 0xa3, + 0x1b, 0xc2, 0x9a, 0x53, 0x79, 0x11, 0xad, 0xd9, +}; +static const uint8_t test_kdf_out[32] = { + 0xdd, 0xbf, 0xc4, 0x40, 0x44, 0x9a, 0xab, 0x41, + 0x31, 0xc6, 0xd8, 0xae, 0xc0, 0x8c, 0xe1, 0x49, + 0x6f, 0x27, 0x02, 0x24, 0x1d, 0x0e, 0x27, 0xcc, + 0x15, 0x5c, 0x5c, 0x7c, 0x3c, 0xda, 0x75, 0xb5, +}; + +#else +#error "Need at least one of SHA-512, SHA-256 or SHA-1" +#endif + +static int ecp_kdf_self_test( void ) +{ + int ret; + ecp_drbg_context kdf_ctx; + mbedtls_mpi scalar; + uint8_t out[sizeof( test_kdf_out )]; + + ecp_drbg_init( &kdf_ctx ); + mbedtls_mpi_init( &scalar ); + memset( out, 0, sizeof( out ) ); + + MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( &scalar, + test_kdf_z, sizeof( test_kdf_z ) ) ); + + MBEDTLS_MPI_CHK( ecp_drbg_seed( &kdf_ctx, + &scalar, sizeof( test_kdf_z ) ) ); + + MBEDTLS_MPI_CHK( ecp_drbg_random( &kdf_ctx, out, sizeof( out ) ) ); + + if( memcmp( out, test_kdf_out, sizeof( out ) ) != 0 ) + ret = -1; + +cleanup: + ecp_drbg_free( &kdf_ctx ); + mbedtls_mpi_free( &scalar ); + + return( ret ); +} +#endif /* ECP_ONE_STEP_KDF */ + /* * Checkup routine */ @@ -3202,6 +3388,24 @@ int mbedtls_ecp_self_test( int verbose ) if( verbose != 0 ) mbedtls_printf( "passed\n" ); +#if defined(ECP_ONE_STEP_KDF) + if( verbose != 0 ) + mbedtls_printf( " ECP test #3 (internal KDF): " ); + + ret = ecp_kdf_self_test(); + if( ret != 0 ) + { + if( verbose != 0 ) + mbedtls_printf( "failed\n" ); + + ret = 1; + goto cleanup; + } + + if( verbose != 0 ) + mbedtls_printf( "passed\n" ); +#endif /* ECP_ONE_STEP_KDF */ + cleanup: if( ret < 0 && verbose != 0 ) diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh index 039ae158c..483173602 100755 --- a/tests/scripts/all.sh +++ b/tests/scripts/all.sh @@ -817,6 +817,69 @@ component_test_no_hmac_drbg () { # so there's little value in running those lengthy tests here. } +component_test_no_drbg_all_hashes () { + # this tests the internal ECP DRBG using a KDF based on SHA-512 + msg "build: Default minus DRBGs" + scripts/config.pl unset MBEDTLS_CTR_DRBG_C + scripts/config.pl unset MBEDTLS_HMAC_DRBG_C + scripts/config.pl unset MBEDTLS_ECDSA_DETERMINISTIC # requires HMAC_DRBG + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_C # requires a DRBG + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_STORAGE_C # requires PSA Crypto + + CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan . + make + + msg "test: Default minus DRBGs" + make test + + # no SSL tests as they all depend on having a DRBG +} + +component_test_no_drbg_no_sha512 () { + # this tests the internal ECP DRBG using a KDF based on SHA-256 + msg "build: Default minus DRBGs minus SHA-512" + scripts/config.pl unset MBEDTLS_CTR_DRBG_C + scripts/config.pl unset MBEDTLS_HMAC_DRBG_C + scripts/config.pl unset MBEDTLS_ECDSA_DETERMINISTIC # requires HMAC_DRBG + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_C # requires a DRBG + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_STORAGE_C # requires PSA Crypto + scripts/config.pl unset MBEDTLS_SHA512_C + + CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan . + make + + msg "test: Default minus DRBGs minus SHA-512" + make test + + # no SSL tests as they all depend on having a DRBG +} + +component_test_no_drbg_no_sha2 () { + # this tests the internal ECP DRBG using a KDF based on SHA-1 + msg "build: Default minus DRBGs minus SHA-2" + scripts/config.pl unset MBEDTLS_CTR_DRBG_C + scripts/config.pl unset MBEDTLS_HMAC_DRBG_C + scripts/config.pl unset MBEDTLS_ECDSA_DETERMINISTIC # requires HMAC_DRBG + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_C # requires a DRBG + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_STORAGE_C # requires PSA Crypto + scripts/config.pl unset MBEDTLS_SHA512_C + scripts/config.pl unset MBEDTLS_SHA256_C + scripts/config.pl unset MBEDTLS_ENTROPY_C # requires SHA-2 + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_C # requires Entropy + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_STORAGE_C # requires PSA Crypto + scripts/config.pl unset MBEDTLS_PSA_CRYPTO_SE_C # requires PSA Crypto + scripts/config.pl unset MBEDTLS_USE_PSA_CRYPTO # requires PSA Crypto + scripts/config.pl unset MBEDTLS_SSL_PROTO_TLS1_2 # requires SHA-2 + + CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan . + make + + msg "test: Default minus DRBGs minus SHA-2" + make test + + # no SSL tests as they all depend on having a DRBG +} + component_test_ecp_no_internal_rng () { msg "build: Default plus ECP_NO_INTERNAL_RNG minus DRBG modules" scripts/config.pl set MBEDTLS_ECP_NO_INTERNAL_RNG