5.3.1 Crypto_Kas_Ecdh_SharedSecret

crypto_Kas_Status_E Crypto_Kas_Ecdh_SharedSecret(
    crypto_HandlerType_E ecdhHandlerType_en, 
    uint8_t *ptr_privKey, 
    uint32_t privKeyLen, 
    uint8_t *ptr_pubKey, 
    uint32_t pubKeyLen, 
    uint8_t *ptr_sharedSecret, 
    uint32_t sharedSecretLen, 
    crypto_EccCurveType_E eccCurveType_en, 
    uint32_t ecdhSessionId
    );

Description

This API is utilized to generate a shared secret using the ECDH algorithm. It requires the ECC private key of one party and the ECC public key of another party as inputs to generate the shared secret. These keys must adhere to the ANSI X9.63 format. Additionally, it's crucial that the ECC keys used in this API are generated from the same curve type. The HW handler currently does not support compressed key format.

Parameters


No.	Argument Type	Argument Name	Type	Description
1	crypto_HandlerType_E	ecdhHandlerType_en	Input	Enum for crypto operation handler i.e., SW, HW
2	uint8_t*	ptr_privKey	Input	Pointer to hold private key in x9.63 format
3	uint32_t	privKeyLen	Input	Length of ECC private key in bytes
4	uint8_t*	ptr_pubKey	Input	Pointer to hold public key in x9.63 format
4	uint32_t	pubKeyLen	Input	Length of ECC public key in bytes
6	uint8_t*	ptr_sharedSecret	Output	Pointer holds the generated Shared Secret
7	uint32_t	sharedSecretLen	Input	Length of Shared Secret in bytes
8	crypto_EccCurveType_E	eccCurveType_en	Input	Curve type used for the ECC keys
9	uint32_t	ecdhSessionId	Input	It defines the session ID, must be more than zero

Returns


Return Type	Description
crypto_Kas_Status_E	Function returns the status of the API.

Prerequisites

To use the HW handler, the algorithm must be enabled in Crypto v4 in MPLAB® Code Configurator.
To use the SW handler, the algorithm must be enabled in wolfCrypt, and linked to Crypto V4 in MPLAB® Code Configurator.

Example

#define sessionID 1
crypto_Kas_Status_E status;
crypto_HandlerType_E handlerType_en = CRYPTO_HANDLER_HW_INTERNAL ;
uint8_t privKey[32] = {/*data*/};
uint32_t privKeyLen = sizeof(privKey);
uint8_t pubKey[65] = {/*data*/}; //64 bytes key and 1 byte compression
uint32_t pubKeyLen = sizeof(pubKey);
uint8_t sharedSecret[64];
uint32_t sharedSecretLen = sizeof(sharedSecret);
crypto_EccCurveType_E eccCurveType_en = CRYPTO_ECC_CURVE_SECP256R1;

status = Crypto_Kas_Ecdh_SharedSecret (
    handlerType_en,
    privKey,
    privKeyLen,
    pubKey,
    pubKeyLen,
    sharedSecret,
    sharedSecretLen,
    eccCurveType_en,
    sessionID
    );

//if using compressed key you must use the CRYPTO_HANDLER_SW_WOLFCRYPT handler. 

//compressed key
handlerType_en = CRYPTO_HANDLER_SW_WOLFCRYPT;
uint8_t pubKeyCompressed[33] = {/*data*/};
uint32_t pubKeyCompressedLen = sizeof(pubKeyCompressed);

status = Crypto_Kas_Ecdh_SharedSecret (
    handlerType_en,
    privKey,
    privKeyLen,
    pubKeyCompressed,
    pubKeyCompressedLen,
    sharedSecret,
    sharedSecretLen,
    eccCurveType_en,
    sessionID
    );