/*
* TLS 1.3 key schedule
*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 ( the "License" ); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#if !defined(MBEDTLS_SSL_TLS1_3_KEYS_H)
#define MBEDTLS_SSL_TLS1_3_KEYS_H
/* This requires MBEDTLS_SSL_TLS1_3_LABEL( idx, name, string ) to be defined at
* the point of use. See e.g. the definition of mbedtls_ssl_tls1_3_labels_union
* below. */
#define MBEDTLS_SSL_TLS1_3_LABEL_LIST \
MBEDTLS_SSL_TLS1_3_LABEL( finished , "finished" ) \
MBEDTLS_SSL_TLS1_3_LABEL( resumption , "resumption" ) \
MBEDTLS_SSL_TLS1_3_LABEL( traffic_upd , "traffic upd" ) \
MBEDTLS_SSL_TLS1_3_LABEL( exporter , "exporter" ) \
MBEDTLS_SSL_TLS1_3_LABEL( key , "key" ) \
MBEDTLS_SSL_TLS1_3_LABEL( iv , "iv" ) \
MBEDTLS_SSL_TLS1_3_LABEL( c_hs_traffic, "c hs traffic" ) \
MBEDTLS_SSL_TLS1_3_LABEL( c_ap_traffic, "c ap traffic" ) \
MBEDTLS_SSL_TLS1_3_LABEL( c_e_traffic , "c e traffic" ) \
MBEDTLS_SSL_TLS1_3_LABEL( s_hs_traffic, "s hs traffic" ) \
MBEDTLS_SSL_TLS1_3_LABEL( s_ap_traffic, "s ap traffic" ) \
MBEDTLS_SSL_TLS1_3_LABEL( s_e_traffic , "s e traffic" ) \
MBEDTLS_SSL_TLS1_3_LABEL( e_exp_master, "e exp master" ) \
MBEDTLS_SSL_TLS1_3_LABEL( res_master , "res master" ) \
MBEDTLS_SSL_TLS1_3_LABEL( exp_master , "exp master" ) \
MBEDTLS_SSL_TLS1_3_LABEL( ext_binder , "ext binder" ) \
MBEDTLS_SSL_TLS1_3_LABEL( res_binder , "res binder" ) \
MBEDTLS_SSL_TLS1_3_LABEL( derived , "derived" )
#define MBEDTLS_SSL_TLS1_3_LABEL( name, string ) \
const unsigned char name [ sizeof(string) - 1 ];
union mbedtls_ssl_tls1_3_labels_union
{
MBEDTLS_SSL_TLS1_3_LABEL_LIST
};
struct mbedtls_ssl_tls1_3_labels_struct
{
MBEDTLS_SSL_TLS1_3_LABEL_LIST
};
#undef MBEDTLS_SSL_TLS1_3_LABEL
extern const struct mbedtls_ssl_tls1_3_labels_struct mbedtls_ssl_tls1_3_labels;
#define MBEDTLS_SSL_TLS1_3_LBL_WITH_LEN( LABEL ) \
mbedtls_ssl_tls1_3_labels.LABEL, \
sizeof(mbedtls_ssl_tls1_3_labels.LABEL)
#define MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_LABEL_LEN \
sizeof( union mbedtls_ssl_tls1_3_labels_union )
/* The maximum length of HKDF contexts used in the TLS 1.3 standard.
* Since contexts are always hashes of message transcripts, this can
* be approximated from above by the maximum hash size. */
#define MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_CONTEXT_LEN \
MBEDTLS_MD_MAX_SIZE
typedef struct
{
unsigned char binder_key [ MBEDTLS_MD_MAX_SIZE ];
unsigned char client_early_traffic_secret [ MBEDTLS_MD_MAX_SIZE ];
unsigned char early_exporter_master_secret[ MBEDTLS_MD_MAX_SIZE ];
} mbedtls_ssl_tls1_3_early_secrets;
typedef struct
{
unsigned char client_handshake_traffic_secret[ MBEDTLS_MD_MAX_SIZE ];
unsigned char server_handshake_traffic_secret[ MBEDTLS_MD_MAX_SIZE ];
} mbedtls_ssl_tls1_3_handshake_secrets;
typedef struct
{
unsigned char client_application_traffic_secret_N[ MBEDTLS_MD_MAX_SIZE ];
unsigned char server_application_traffic_secret_N[ MBEDTLS_MD_MAX_SIZE ];
unsigned char exporter_master_secret [ MBEDTLS_MD_MAX_SIZE ];
unsigned char resumption_master_secret [ MBEDTLS_MD_MAX_SIZE ];
} mbedtls_ssl_tls1_3_application_secrets;
/* Maximum desired length for expanded key material generated
* by HKDF-Expand-Label.
*
* Warning: If this ever needs to be increased, the implementation
* ssl_tls1_3_hkdf_encode_label() in ssl_tls13_keys.c needs to be
* adjusted since it currently assumes that HKDF key expansion
* is never used with more than 255 Bytes of output. */
#define MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_EXPANSION_LEN 255
/**
* \brief The \c HKDF-Expand-Label function from
* the TLS 1.3 standard RFC 8446.
*
*
* HKDF-Expand-Label( Secret, Label, Context, Length ) =
* HKDF-Expand( Secret, HkdfLabel, Length )
*
*
* \param hash_alg The identifier for the hash algorithm to use.
* \param secret The \c Secret argument to \c HKDF-Expand-Label.
* This must be a readable buffer of length \p slen Bytes.
* \param slen The length of \p secret in Bytes.
* \param label The \c Label argument to \c HKDF-Expand-Label.
* This must be a readable buffer of length \p llen Bytes.
* \param llen The length of \p label in Bytes.
* \param ctx The \c Context argument to \c HKDF-Expand-Label.
* This must be a readable buffer of length \p clen Bytes.
* \param clen The length of \p context in Bytes.
* \param buf The destination buffer to hold the expanded secret.
* This must be a writable buffer of length \p blen Bytes.
* \param blen The desired size of the expanded secret in Bytes.
*
* \returns \c 0 on success.
* \return A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_hkdf_expand_label(
mbedtls_md_type_t hash_alg,
const unsigned char *secret, size_t slen,
const unsigned char *label, size_t llen,
const unsigned char *ctx, size_t clen,
unsigned char *buf, size_t blen );
/**
* \brief This function is part of the TLS 1.3 key schedule.
* It extracts key and IV for the actual client/server traffic
* from the client/server traffic secrets.
*
* From RFC 8446:
*
*
* [sender]_write_key = HKDF-Expand-Label(Secret, "key", "", key_length)
* [sender]_write_iv = HKDF-Expand-Label(Secret, "iv", "", iv_length)*
*
*
* \param hash_alg The identifier for the hash algorithm to be used
* for the HKDF-based expansion of the secret.
* \param client_secret The client traffic secret.
* This must be a readable buffer of size \p slen Bytes
* \param server_secret The server traffic secret.
* This must be a readable buffer of size \p slen Bytes
* \param slen Length of the secrets \p client_secret and
* \p server_secret in Bytes.
* \param key_len The desired length of the key to be extracted in Bytes.
* \param iv_len The desired length of the IV to be extracted in Bytes.
* \param keys The address of the structure holding the generated
* keys and IVs.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_make_traffic_keys(
mbedtls_md_type_t hash_alg,
const unsigned char *client_secret,
const unsigned char *server_secret,
size_t slen, size_t key_len, size_t iv_len,
mbedtls_ssl_key_set *keys );
#define MBEDTLS_SSL_TLS1_3_CONTEXT_UNHASHED 0
#define MBEDTLS_SSL_TLS1_3_CONTEXT_HASHED 1
/**
* \brief The \c Derive-Secret function from the TLS 1.3 standard RFC 8446.
*
*
* Derive-Secret( Secret, Label, Messages ) =
* HKDF-Expand-Label( Secret, Label,
* Hash( Messages ),
* Hash.Length ) )
*
*
* \param hash_alg The identifier for the hash function used for the
* applications of HKDF.
* \param secret The \c Secret argument to the \c Derive-Secret function.
* This must be a readable buffer of length \p slen Bytes.
* \param slen The length of \p secret in Bytes.
* \param label The \c Label argument to the \c Derive-Secret function.
* This must be a readable buffer of length \p llen Bytes.
* \param llen The length of \p label in Bytes.
* \param ctx The hash of the \c Messages argument to the
* \c Derive-Secret function, or the \c Messages argument
* itself, depending on \p context_already_hashed.
* \param clen The length of \p hash.
* \param ctx_hashed This indicates whether the \p ctx contains the hash of
* the \c Messages argument in the application of the
* \c Derive-Secret function
* (value MBEDTLS_SSL_TLS1_3_CONTEXT_HASHED), or whether
* it is the content of \c Messages itself, in which case
* the function takes care of the hashing
* (value MBEDTLS_SSL_TLS1_3_CONTEXT_UNHASHED).
* \param dstbuf The target buffer to write the output of
* \c Derive-Secret to. This must be a writable buffer of
* size \p buflen Bytes.
* \param buflen The length of \p dstbuf in Bytes.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_derive_secret(
mbedtls_md_type_t hash_alg,
const unsigned char *secret, size_t slen,
const unsigned char *label, size_t llen,
const unsigned char *ctx, size_t clen,
int ctx_hashed,
unsigned char *dstbuf, size_t buflen );
/**
* \brief Derive TLS 1.3 early data key material from early secret.
*
* This is a small wrapper invoking mbedtls_ssl_tls1_3_derive_secret()
* with the appropriate labels.
*
*
* Early Secret
* |
* +-----> Derive-Secret(., "c e traffic", ClientHello)
* | = client_early_traffic_secret
* |
* +-----> Derive-Secret(., "e exp master", ClientHello)
* . = early_exporter_master_secret
* .
* .
*
*
* \note To obtain the actual key and IV for the early data traffic,
* the client secret derived by this function need to be
* further processed by mbedtls_ssl_tls1_3_make_traffic_keys().
*
* \note The binder key, which is also generated from the early secret,
* is omitted here. Its calculation is part of the separate routine
* mbedtls_ssl_tls1_3_create_psk_binder().
*
* \param md_type The hash algorithm associated with the PSK for which
* early data key material is being derived.
* \param early_secret The early secret from which the early data key material
* should be derived. This must be a readable buffer whose
* length is the digest size of the hash algorithm
* represented by \p md_size.
* \param transcript The transcript of the handshake so far, calculated with
* respect to \p md_type. This must be a readable buffer
* whose length is the digest size of the hash algorithm
* represented by \p md_size.
* \param derived The address of the structure in which to store
* the early data key material.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_derive_early_secrets(
mbedtls_md_type_t md_type,
unsigned char const *early_secret,
unsigned char const *transcript, size_t transcript_len,
mbedtls_ssl_tls1_3_early_secrets *derived );
/**
* \brief Derive TLS 1.3 handshake key material from the handshake secret.
*
* This is a small wrapper invoking mbedtls_ssl_tls1_3_derive_secret()
* with the appropriate labels from the standard.
*
*
* Handshake Secret
* |
* +-----> Derive-Secret( ., "c hs traffic",
* | ClientHello...ServerHello )
* | = client_handshake_traffic_secret
* |
* +-----> Derive-Secret( ., "s hs traffic",
* . ClientHello...ServerHello )
* . = server_handshake_traffic_secret
* .
*
*
* \note To obtain the actual key and IV for the encrypted handshake traffic,
* the client and server secret derived by this function need to be
* further processed by mbedtls_ssl_tls1_3_make_traffic_keys().
*
* \param md_type The hash algorithm associated with the ciphersuite
* that's being used for the connection.
* \param handshake_secret The handshake secret from which the handshake key
* material should be derived. This must be a readable
* buffer whose length is the digest size of the hash
* algorithm represented by \p md_size.
* \param transcript The transcript of the handshake so far, calculated
* with respect to \p md_type. This must be a readable
* buffer whose length is the digest size of the hash
* algorithm represented by \p md_size.
* \param derived The address of the structure in which to
* store the handshake key material.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_derive_handshake_secrets(
mbedtls_md_type_t md_type,
unsigned char const *handshake_secret,
unsigned char const *transcript, size_t transcript_len,
mbedtls_ssl_tls1_3_handshake_secrets *derived );
/**
* \brief Derive TLS 1.3 application key material from the master secret.
*
* This is a small wrapper invoking mbedtls_ssl_tls1_3_derive_secret()
* with the appropriate labels from the standard.
*
*
* Master Secret
* |
* +-----> Derive-Secret( ., "c ap traffic",
* | ClientHello...server Finished )
* | = client_application_traffic_secret_0
* |
* +-----> Derive-Secret( ., "s ap traffic",
* | ClientHello...Server Finished )
* | = server_application_traffic_secret_0
* |
* +-----> Derive-Secret( ., "exp master",
* . ClientHello...server Finished)
* . = exporter_master_secret
* .
*
*
* \note To obtain the actual key and IV for the (0-th) application traffic,
* the client and server secret derived by this function need to be
* further processed by mbedtls_ssl_tls1_3_make_traffic_keys().
*
* \param md_type The hash algorithm associated with the ciphersuite
* that's being used for the connection.
* \param master_secret The master secret from which the application key
* material should be derived. This must be a readable
* buffer whose length is the digest size of the hash
* algorithm represented by \p md_size.
* \param transcript The transcript of the handshake up to and including
* the ServerFinished message, calculated with respect
* to \p md_type. This must be a readable buffer whose
* length is the digest size of the hash algorithm
* represented by \p md_type.
* \param derived The address of the structure in which to
* store the application key material.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_derive_application_secrets(
mbedtls_md_type_t md_type,
unsigned char const *master_secret,
unsigned char const *transcript, size_t transcript_len,
mbedtls_ssl_tls1_3_application_secrets *derived );
/**
* \brief Derive TLS 1.3 resumption master secret from the master secret.
*
* This is a small wrapper invoking mbedtls_ssl_tls1_3_derive_secret()
* with the appropriate labels from the standard.
*
* \param md_type The hash algorithm used in the application for which
* key material is being derived.
* \param application_secret The application secret from which the resumption master
* secret should be derived. This must be a readable
* buffer whose length is the digest size of the hash
* algorithm represented by \p md_size.
* \param transcript The transcript of the handshake up to and including
* the ClientFinished message, calculated with respect
* to \p md_type. This must be a readable buffer whose
* length is the digest size of the hash algorithm
* represented by \p md_type.
* \param transcript_len The length of \p transcript in Bytes.
* \param derived The address of the structure in which to
* store the resumption master secret.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_derive_resumption_master_secret(
mbedtls_md_type_t md_type,
unsigned char const *application_secret,
unsigned char const *transcript, size_t transcript_len,
mbedtls_ssl_tls1_3_application_secrets *derived );
/**
* \brief Compute the next secret in the TLS 1.3 key schedule
*
* The TLS 1.3 key schedule proceeds as follows to compute
* the three main secrets during the handshake: The early
* secret for early data, the handshake secret for all
* other encrypted handshake messages, and the master
* secret for all application traffic.
*
*
* 0
* |
* v
* PSK -> HKDF-Extract = Early Secret
* |
* v
* Derive-Secret( ., "derived", "" )
* |
* v
* (EC)DHE -> HKDF-Extract = Handshake Secret
* |
* v
* Derive-Secret( ., "derived", "" )
* |
* v
* 0 -> HKDF-Extract = Master Secret
*
*
* Each of the three secrets in turn is the basis for further
* key derivations, such as the derivation of traffic keys and IVs;
* see e.g. mbedtls_ssl_tls1_3_make_traffic_keys().
*
* This function implements one step in this evolution of secrets:
*
*
* old_secret
* |
* v
* Derive-Secret( ., "derived", "" )
* |
* v
* input -> HKDF-Extract = new_secret
*
*
* \param hash_alg The identifier for the hash function used for the
* applications of HKDF.
* \param secret_old The address of the buffer holding the old secret
* on function entry. If not \c NULL, this must be a
* readable buffer whose size matches the output size
* of the hash function represented by \p hash_alg.
* If \c NULL, an all \c 0 array will be used instead.
* \param input The address of the buffer holding the additional
* input for the key derivation (e.g., the PSK or the
* ephemeral (EC)DH secret). If not \c NULL, this must be
* a readable buffer whose size \p input_len Bytes.
* If \c NULL, an all \c 0 array will be used instead.
* \param input_len The length of \p input in Bytes.
* \param secret_new The address of the buffer holding the new secret
* on function exit. This must be a writable buffer
* whose size matches the output size of the hash
* function represented by \p hash_alg.
* This may be the same as \p secret_old.
*
* \returns \c 0 on success.
* \returns A negative error code on failure.
*/
int mbedtls_ssl_tls1_3_evolve_secret(
mbedtls_md_type_t hash_alg,
const unsigned char *secret_old,
const unsigned char *input, size_t input_len,
unsigned char *secret_new );
#endif /* MBEDTLS_SSL_TLS1_3_KEYS_H */