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Introduce macros for max-{IV,block,key}-size for ciphers used in TLS

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See the documentation in ssl_internal.h that this commit introduces
for more information.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit is contained in:
Hanno Becker 2020-09-08 11:29:11 +01:00
parent 815869ac9c
commit 1588983ef0
2 changed files with 36 additions and 7 deletions
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13
include/mbedtls/cipher.h
View file

@ -227,17 +227,24 @@ enum {
}; };
/** Maximum length of any IV, in Bytes. */ /** Maximum length of any IV, in Bytes. */
/* This should ideally be derived automatically from list of ciphers. */ /* This should ideally be derived automatically from list of ciphers.
* This should be kept in sync with MBEDTLS_SSL_MAX_IV_LENGTH defined
* in ssl_internal.h. */
#define MBEDTLS_MAX_IV_LENGTH 16 #define MBEDTLS_MAX_IV_LENGTH 16
/** Maximum block size of any cipher, in Bytes. */ /** Maximum block size of any cipher, in Bytes. */
/* This should ideally be derived automatically from list of ciphers. */ /* This should ideally be derived automatically from list of ciphers.
* This should be kept in sync with MBEDTLS_SSL_MAX_BLOCK_LENGTH defined
* in ssl_internal.h. */
#define MBEDTLS_MAX_BLOCK_LENGTH 16 #define MBEDTLS_MAX_BLOCK_LENGTH 16
/** Maximum key length, in Bytes. */ /** Maximum key length, in Bytes. */
/* This should ideally be derived automatically from list of ciphers. /* This should ideally be derived automatically from list of ciphers.
* For now, only check whether XTS is enabled which uses 64 Byte keys, * For now, only check whether XTS is enabled which uses 64 Byte keys,
* and use 32 Bytes as an upper bound for the maximum key length otherwise. */ * and use 32 Bytes as an upper bound for the maximum key length otherwise.
* This should be kept in sync with MBEDTLS_SSL_MAX_BLOCK_LENGTH defined
* in ssl_internal.h, which however deliberately ignores the case of XTS
* since the latter isn't used in SSL/TLS. */
#if defined(MBEDTLS_CIPHER_MODE_XTS) #if defined(MBEDTLS_CIPHER_MODE_XTS)
#define MBEDTLS_MAX_KEY_LENGTH 64 #define MBEDTLS_MAX_KEY_LENGTH 64
#else #else

30
include/mbedtls/ssl_internal.h
View file

@ -379,7 +379,29 @@ typedef int mbedtls_ssl_tls_prf_cb( const unsigned char *secret, size_t slen,
const unsigned char *random, size_t rlen, const unsigned char *random, size_t rlen,
unsigned char *dstbuf, size_t dlen ); unsigned char *dstbuf, size_t dlen );
/* cipher.h exports the maximum IV, key and block length from all
* all ciphers enabled in the config, regardless of whether those
* ciphers are actually usable in SSL/TLS. Notably, XTS is enabled
* in the default configuration and uses 64 Byte keys, but it is
* not used for record protection in SSL/TLS.
*
* In order to prevent unnecessary inflation of key structures,
* we introduce SSL-specific variants of the max-{key,block,IV}
* macros here which are meant to only take those ciphers into
* account which can be negotiated in SSL/TLS.
*
* Since the current definitions of MBEDTLS_MAX_{KEY|BLOCK|IV}_LENGTH
* in cipher.h are rough overapproximations of the real maxima, here
* we content ourselves with defining replicating those overapproximations
* for the maximum block and IV length, and excluding XTS from the
* computation of the maximum key length. */
#define MBEDTLS_SSL_MAX_BLOCK_LENGTH 16
#define MBEDTLS_SSL_MAX_IV_LENGTH 16
#define MBEDTLS_SSL_MAX_KEY_LENGTH 32
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL) #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
/** /**
* \brief The data structure holding the cryptographic material (key and IV) * \brief The data structure holding the cryptographic material (key and IV)
* used for record protection in TLS 1.3. * used for record protection in TLS 1.3.
@ -387,13 +409,13 @@ typedef int mbedtls_ssl_tls_prf_cb( const unsigned char *secret, size_t slen,
struct mbedtls_ssl_key_set struct mbedtls_ssl_key_set
{ {
/*! The key for client->server records. */ /*! The key for client->server records. */
unsigned char client_write_key[ MBEDTLS_MAX_KEY_LENGTH ]; unsigned char client_write_key[ MBEDTLS_SSL_MAX_KEY_LENGTH ];
/*! The key for server->client records. */ /*! The key for server->client records. */
unsigned char server_write_key[ MBEDTLS_MAX_KEY_LENGTH ]; unsigned char server_write_key[ MBEDTLS_SSL_MAX_KEY_LENGTH ];
/*! The IV for client->server records. */ /*! The IV for client->server records. */
unsigned char client_write_iv[ MBEDTLS_MAX_IV_LENGTH ]; unsigned char client_write_iv[ MBEDTLS_SSL_MAX_IV_LENGTH ];
/*! The IV for server->client records. */ /*! The IV for server->client records. */
unsigned char server_write_iv[ MBEDTLS_MAX_IV_LENGTH ]; unsigned char server_write_iv[ MBEDTLS_SSL_MAX_IV_LENGTH ];
size_t key_len; /*!< The length of client_write_key and size_t key_len; /*!< The length of client_write_key and
* server_write_key, in Bytes. */ * server_write_key, in Bytes. */