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Implement TLS 1.3 key evolution function

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Signed-off-by: Hanno Becker <hanno.becker@arm.com>
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Hanno Becker
2020-08-20 13:42:46 +01:00
parent e4849d10a6
commit e9cccb440c
2 changed files with 135 additions and 0 deletions
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73
library/ssl_tls13_keys.h
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@ -182,6 +182,79 @@ int mbedtls_ssl_tls1_3_derive_secret(
int context_already_hashed,
unsigned char *dstbuf, size_t buflen );
/**
* \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.
*
* <tt>
* 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
* </tt>
*
* 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:
*
* <tt>
* old_secret
* |
* v
* Derive-Secret( ., "derived", "" )
* |
* v
* input -> HKDF-Extract = new_secret
* </tt>
*
* \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_PROTO_TLS1_3_EXPERIMENTAL */
#endif /* MBEDTLS_SSL_TLS1_3_KEYS_H */