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New function to get the raw shared secret from key agreement

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The normal way is to pass the shared secret to a key derivation.
Having an ad hoc function will allow us to simplify the possible
behaviors of key agreement and get rid of "key selection" algorithms
which are a hard-to-understand invention of this API.
This commit is contained in:
Gilles Peskine 2019-01-18 16:42:29 +01:00
parent 5dcd3ce598
commit 769c7a66ac
1 changed files with 52 additions and 0 deletions
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52
include/psa/crypto.h
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@ -2279,6 +2279,58 @@ psa_status_t psa_key_agreement(psa_crypto_generator_t *generator,
const uint8_t *peer_key,
size_t peer_key_length);
/** Perform a key agreement and use the shared secret as input to a key
* derivation.
*
* A key agreement algorithm takes two inputs: a private key \p private_key
* a public key \p peer_key.
*
* \warning The raw result of a key agreement algorithm such as finite-field
* Diffie-Hellman or elliptic curve Diffie-Hellman has biases and should
* not be used directly as key material. It should instead be passed as
* input to a key derivation algorithm. To chain a key agreement with
* a key derivation, use psa_key_agreement() and other functions from
* the key derivation and generator interface.
*
* \param private_key Handle to the private key to use.
* \param[in] peer_key Public key of the peer. It must be
* in the same format that psa_import_key()
* accepts. The standard formats for public
* keys are documented in the documentation
* of psa_export_public_key().
* \param peer_key_length Size of \p peer_key in bytes.
* \param[out] output Buffer where the decrypted message is to
* be written.
* \param output_size Size of the \c output buffer in bytes.
* \param[out] output_length On success, the number of bytes
* that make up the returned output.
*
* \retval #PSA_SUCCESS
* Success.
* \retval #PSA_ERROR_INVALID_HANDLE
* \retval #PSA_ERROR_EMPTY_SLOT
* \retval #PSA_ERROR_NOT_PERMITTED
* \retval #PSA_ERROR_INVALID_ARGUMENT
* \p alg is not a key agreement algorithm
* \retval #PSA_ERROR_INVALID_ARGUMENT
* \p private_key is not compatible with \p alg,
* or \p peer_key is not valid for \p alg or not compatible with
* \p private_key.
* \retval #PSA_ERROR_NOT_SUPPORTED
* \p alg is not a supported key agreement algorithm.
* \retval #PSA_ERROR_INSUFFICIENT_MEMORY
* \retval #PSA_ERROR_COMMUNICATION_FAILURE
* \retval #PSA_ERROR_HARDWARE_FAILURE
* \retval #PSA_ERROR_TAMPERING_DETECTED
*/
psa_status_t psa_key_agreement_raw_shared_secret(psa_algorithm_t alg,
psa_key_handle_t private_key,
const uint8_t *peer_key,
size_t peer_key_length,
uint8_t *output,
size_t output_size,
size_t *output_length);
/**@}*/
/** \defgroup random Random generation