Algorithms - Curve25519

Functions
int	wc_curve25519_make_key (WC_RNG *rng, int keysize, curve25519_key *key)
	This function generates a Curve25519 key using the given random number generator, rng, of the size given (keysize), and stores it in the given curve25519_key structure. It should be called after the key structure has been initialized through wc_curve25519_init(). More...
int	wc_curve25519_shared_secret (curve25519_key *private_key, curve25519_key *public_key, byte *out, word32 *outlen)
	This function computes a shared secret key given a secret private key and a received public key. It stores the generated secret key in the buffer out and assigns the variable of the secret key to outlen. Only supports big endian. More...
int	wc_curve25519_shared_secret_ex (curve25519_key *private_key, curve25519_key *public_key, byte *out, word32 *outlen, int endian)
	This function computes a shared secret key given a secret private key and a received public key. It stores the generated secret key in the buffer out and assigns the variable of the secret key to outlen. Supports both big and little endian. More...
int	wc_curve25519_init (curve25519_key *key)
	This function initializes a Curve25519 key. It should be called before generating a key for the structure. More...
void	wc_curve25519_free (curve25519_key *key)
	This function frees a Curve25519 object. More...
int	wc_curve25519_import_private (const byte *priv, word32 privSz, curve25519_key *key)
	This function imports a curve25519 private key only. (Big endian). More...
int	wc_curve25519_import_private_ex (const byte *priv, word32 privSz, curve25519_key *key, int endian)
	curve25519 private key import only. (Big or Little endian). More...
int	wc_curve25519_import_private_raw (const byte *priv, word32 privSz, const byte *pub, word32 pubSz, curve25519_key *key)
	This function imports a public-private key pair into a curve25519_key structure. Big endian only. More...
int	wc_curve25519_import_private_raw_ex (const byte *priv, word32 privSz, const byte *pub, word32 pubSz, curve25519_key *key, int endian)
	This function imports a public-private key pair into a curve25519_key structure. Supports both big and little endian. More...
int	wc_curve25519_export_private_raw (curve25519_key *key, byte *out, word32 *outLen)
	This function exports a private key from a curve25519_key structure and stores it in the given out buffer. It also sets outLen to be the size of the exported key. Big Endian only. More...
int	wc_curve25519_export_private_raw_ex (curve25519_key *key, byte *out, word32 *outLen, int endian)
	This function exports a private key from a curve25519_key structure and stores it in the given out buffer. It also sets outLen to be the size of the exported key. Can specify whether it's big or little endian. More...
int	wc_curve25519_import_public (const byte *in, word32 inLen, curve25519_key *key)
	This function imports a public key from the given in buffer and stores it in the curve25519_key structure. More...
int	wc_curve25519_import_public_ex (const byte *in, word32 inLen, curve25519_key *key, int endian)
	This function imports a public key from the given in buffer and stores it in the curve25519_key structure. More...
int	wc_curve25519_check_public (const byte *pub, word32 pubSz, int endian)
	This function checks that a public key buffer holds a valid Curve25519 key value given the endian ordering. More...
int	wc_curve25519_export_public (curve25519_key *key, byte *out, word32 *outLen)
	This function exports a public key from the given key structure and stores the result in the out buffer. Big endian only. More...
int	wc_curve25519_export_public_ex (curve25519_key *key, byte *out, word32 *outLen, int endian)
	This function exports a public key from the given key structure and stores the result in the out buffer. Supports both big and little endian. More...
int	wc_curve25519_export_key_raw (curve25519_key *key, byte *priv, word32 *privSz, byte *pub, word32 *pubSz)
	Export Curve25519 key pair. Big endian only. More...
int	wc_curve25519_export_key_raw_ex (curve25519_key *key, byte *priv, word32 *privSz, byte *pub, word32 *pubSz, int endian)
	Export curve25519 key pair. Big or little endian. More...
int	wc_curve25519_size (curve25519_key *key)
	This function returns the key size of the given key structure. More...

Detailed Description

Function Documentation

wc_curve25519_check_public()

int wc_curve25519_check_public	(	const byte *	pub,
		word32	pubSz,
		int	endian
	)

This function checks that a public key buffer holds a valid Curve25519 key value given the endian ordering.

Returns

0 Returned when the public key value is valid.

ECC_BAD_ARG_E Returned if the public key value is not valid.

BAD_FUNC_ARG Returned if any of the input parameters are NULL.

Parameters

[in]	pub	Pointer to the buffer containing the public key to check.
[in]	pubLen	Length of the public key to check.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte pub[] = { Contents of public key };
 
ret = wc_curve25519_check_public_ex(pub, sizeof(pub), EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error importing key
}

See also

wc_curve25519_init

wc_curve25519_import_public

wc_curve25519_import_public_ex

wc_curve25519_size

wc_curve25519_export_key_raw()

int wc_curve25519_export_key_raw	(	curve25519_key *	key,
		byte *	priv,
		word32 *	privSz,
		byte *	pub,
		word32 *	pubSz
	)

Export Curve25519 key pair. Big endian only.

Returns

0 Returned on successfully exporting the key pair from the curve25519_key structure.

BAD_FUNC_ARG Returned if any input parameters are NULL.

ECC_BAD_ARG_E Returned if privSz is less than CURVE25519_KEY_SIZE or pubSz is less than CURVE25519_PUB_KEY_SIZE.

Parameters

[in]	key	Pointer to the curve448_key structure in from which to export the key pair.
[out]	priv	Pointer to the buffer in which to store the private key.
[in,out]	privSz	On in, is the size of the priv buffer in bytes. On out, will store the bytes written to the priv buffer.
[out]	pub	Pointer to the buffer in which to store the public key.
[in,out]	pubSz	On in, is the size of the pub buffer in bytes. On out, will store the bytes written to the pub buffer.

Example

int ret;
 
byte pub[32];
byte priv[32];
int pubSz;
int privSz;
 
curve25519_key key;
// initialize and make key
 
ret = wc_curve25519_export_key_raw(&key, priv, &privSz, pub, &pubSz);
if (ret != 0) {
    // error exporting key
}

See also

wc_curve25519_export_key_raw_ex

wc_curve25519_export_private_raw

wc_curve25519_export_key_raw_ex()

int wc_curve25519_export_key_raw_ex	(	curve25519_key *	key,
		byte *	priv,
		word32 *	privSz,
		byte *	pub,
		word32 *	pubSz,
		int	endian
	)

Export curve25519 key pair. Big or little endian.

Returns

0 Returned on successfully exporting the key pair from the curve25519_key structure.

BAD_FUNC_ARG Returned if any input parameters are NULL.

ECC_BAD_ARG_E Returned if privSz is less than CURVE25519_KEY_SIZE or pubSz is less than CURVE25519_PUB_KEY_SIZE.

Parameters

[in]	key	Pointer to the curve448_key structure in from which to export the key pair.
[out]	priv	Pointer to the buffer in which to store the private key.
[in,out]	privSz	On in, is the size of the priv buffer in bytes. On out, will store the bytes written to the priv buffer.
[out]	pub	Pointer to the buffer in which to store the public key.
[in,out]	pubSz	On in, is the size of the pub buffer in bytes. On out, will store the bytes written to the pub buffer.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte pub[32];
byte priv[32];
int pubSz;
int privSz;
 
curve25519_key key;
// initialize and make key
 
ret = wc_curve25519_export_key_raw_ex(&key,priv, &privSz, pub, &pubSz,
        EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error exporting key
}

See also

wc_curve25519_export_key_raw

wc_curve25519_export_private_raw_ex

wc_curve25519_export_public_ex

wc_curve25519_export_private_raw()

int wc_curve25519_export_private_raw	(	curve25519_key *	key,
		byte *	out,
		word32 *	outLen
	)

This function exports a private key from a curve25519_key structure and stores it in the given out buffer. It also sets outLen to be the size of the exported key. Big Endian only.

Returns

0 Returned on successfully exporting the private key from the curve25519_key structure.

BAD_FUNC_ARG Returned if any input parameters are NULL.

ECC_BAD_ARG_E Returned if wc_curve25519_size() is not equal to key.

Parameters

[in]	key	Pointer to the structure from which to export the key.
[out]	out	Pointer to the buffer in which to store the exported key.
[in,out]	outLen	On in, is the size of the out in bytes. On out, will store the bytes written to the output buffer.

Example

int ret;
byte priv[32];
int privSz;
 
curve25519_key key;
// initialize and make key
 
ret = wc_curve25519_export_private_raw(&key, priv, &privSz);
if (ret != 0) {
    // error exporting key
}

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_import_private_raw

wc_curve25519_export_private_raw_ex

wc_curve25519_export_private_raw_ex()

int wc_curve25519_export_private_raw_ex	(	curve25519_key *	key,
		byte *	out,
		word32 *	outLen,
		int	endian
	)

This function exports a private key from a curve25519_key structure and stores it in the given out buffer. It also sets outLen to be the size of the exported key. Can specify whether it's big or little endian.

Returns

0 Returned on successfully exporting the private key from the curve25519_key structure.

BAD_FUNC_ARG Returned if any input parameters are NULL.

ECC_BAD_ARG_E Returned if wc_curve25519_size() is not equal to key.

Parameters

[in]	key	Pointer to the structure from which to export the key.
[out]	out	Pointer to the buffer in which to store the exported key.
[in,out]	outLen	On in, is the size of the out in bytes. On out, will store the bytes written to the output buffer.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte priv[32];
int privSz;
curve25519_key key;
// initialize and make key
ret = wc_curve25519_export_private_raw_ex(&key, priv, &privSz,
        EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error exporting key
}

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_import_private_raw

wc_curve25519_export_private_raw

wc_curve25519_size

wc_curve25519_export_public()

int wc_curve25519_export_public	(	curve25519_key *	key,
		byte *	out,
		word32 *	outLen
	)

This function exports a public key from the given key structure and stores the result in the out buffer. Big endian only.

Returns

0 Returned on successfully exporting the public key from the curve25519_key structure.

ECC_BAD_ARG_E Returned if outLen is less than CURVE25519_PUB_KEY_SIZE.

BAD_FUNC_ARG Returned if any of the input parameters are NULL.

Parameters

[in]	key	Pointer to the curve25519_key structure in from which to export the key.
[out]	out	Pointer to the buffer in which to store the public key.
[in,out]	outLen	On in, is the size of the out in bytes. On out, will store the bytes written to the output buffer.

Example

int ret;
 
byte pub[32];
int pubSz;
 
curve25519_key key;
// initialize and make key
ret = wc_curve25519_export_public(&key, pub, &pubSz);
if (ret != 0) {
    // error exporting key
}

See also

wc_curve25519_init

wc_curve25519_export_private_raw

wc_curve25519_import_public

wc_curve25519_export_public_ex()

int wc_curve25519_export_public_ex	(	curve25519_key *	key,
		byte *	out,
		word32 *	outLen,
		int	endian
	)

This function exports a public key from the given key structure and stores the result in the out buffer. Supports both big and little endian.

Returns

0 Returned on successfully exporting the public key from the curve25519_key structure.

ECC_BAD_ARG_E Returned if outLen is less than CURVE25519_PUB_KEY_SIZE.

BAD_FUNC_ARG Returned if any of the input parameters are NULL.

Parameters

[in]	key	Pointer to the curve25519_key structure in from which to export the key.
[out]	out	Pointer to the buffer in which to store the public key.
[in,out]	outLen	On in, is the size of the out in bytes. On out, will store the bytes written to the output buffer.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte pub[32];
int pubSz;
 
curve25519_key key;
// initialize and make key
 
ret = wc_curve25519_export_public_ex(&key, pub, &pubSz, EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error exporting key
}

See also

wc_curve25519_init

wc_curve25519_export_private_raw

wc_curve25519_import_public

wc_curve25519_free()

void wc_curve25519_free

(

curve25519_key *

key

)

This function frees a Curve25519 object.

Parameters

[in,out]

key

Pointer to the key object to free.

Example

curve25519_key privKey;
// initialize key, use it to generate shared secret key
wc_curve25519_free(&privKey);

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_import_private()

int wc_curve25519_import_private	(	const byte *	priv,
		word32	privSz,
		curve25519_key *	key
	)

This function imports a curve25519 private key only. (Big endian).

Returns

0 Returned on successfully importing private key.

BAD_FUNC_ARG Returns if key or priv is null.

ECC_BAD_ARG_E Returns if privSz is not equal to CURVE25519_KEY_SIZE.

Parameters

[in]	priv	Pointer to a buffer containing the private key to import.
[in]	privSz	Length of the private key to import.
[in,out]	key	Pointer to the structure in which to store the imported key.

Example

int ret;
 
byte priv[] = { Contents of private key };
curve25519_key key;
wc_curve25519_init(&key);
 
ret = wc_curve25519_import_private(priv, sizeof(priv), &key);
if (ret != 0) {
    // error importing keys
}

See also

wc_curve25519_import_private_ex

wc_curve25519_size

wc_curve25519_import_private_ex()

int wc_curve25519_import_private_ex	(	const byte *	priv,
		word32	privSz,
		curve25519_key *	key,
		int	endian
	)

curve25519 private key import only. (Big or Little endian).

Returns

0 Returned on successfully importing private key.

BAD_FUNC_ARG Returns if key or priv is null.

ECC_BAD_ARG_E Returns if privSz is not equal to CURVE25519_KEY_SIZE.

Parameters

[in]	priv	Pointer to a buffer containing the private key to import.
[in]	privSz	Length of the private key to import.
[in,out]	key	Pointer to the structure in which to store the imported key.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte priv[] = { // Contents of private key };
curve25519_key key;
wc_curve25519_init(&key);
 
ret = wc_curve25519_import_private_ex(priv, sizeof(priv), &key,
        EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error importing keys
}

See also

wc_curve25519_import_private

wc_curve25519_size

wc_curve25519_import_private_raw()

int wc_curve25519_import_private_raw	(	const byte *	priv,
		word32	privSz,
		const byte *	pub,
		word32	pubSz,
		curve25519_key *	key
	)

This function imports a public-private key pair into a curve25519_key structure. Big endian only.

Returns

0 Returned on importing into the curve25519_key structure

BAD_FUNC_ARG Returns if any of the input parameters are null.

ECC_BAD_ARG_E Returned if the input key’s key size does not match the public or private key sizes.

Parameters

[in]	priv	Pointer to a buffer containing the private key to import.
[in]	privSz	Length of the private key to import.
[in]	pub	Pointer to a buffer containing the public key to import.
[in]	pubSz	Length of the public key to import.
[in,out]	key	Pointer to the structure in which to store the imported keys.

Example

int ret;
 
byte priv[32];
byte pub[32];
// initialize with public and private keys
curve25519_key key;
 
wc_curve25519_init(&key);
// initialize key
 
ret = wc_curve25519_import_private_raw(&priv, sizeof(priv), pub,
        sizeof(pub), &key);
if (ret != 0) {
    // error importing keys
}

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_import_public

wc_curve25519_export_private_raw

wc_curve25519_import_private_raw_ex()

int wc_curve25519_import_private_raw_ex	(	const byte *	priv,
		word32	privSz,
		const byte *	pub,
		word32	pubSz,
		curve25519_key *	key,
		int	endian
	)

This function imports a public-private key pair into a curve25519_key structure. Supports both big and little endian.

Returns

0 Returned on importing into the curve25519_key structure

BAD_FUNC_ARG Returns if any of the input parameters are null.

ECC_BAD_ARG_E Returned if or the input key’s key size does not match the public or private key sizes

Parameters

[in]	priv	Pointer to a buffer containing the private key to import.
[in]	privSz	Length of the private key to import.
[in]	pub	Pointer to a buffer containing the public key to import.
[in]	pubSz	Length of the public key to import.
[in,out]	key	Pointer to the structure in which to store the imported keys.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
byte priv[32];
byte pub[32];
// initialize with public and private keys
curve25519_key key;
 
wc_curve25519_init(&key);
// initialize key
 
ret = wc_curve25519_import_private_raw_ex(&priv, sizeof(priv), pub,
        sizeof(pub), &key, EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error importing keys
}

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_import_public

wc_curve25519_export_private_raw

wc_curve25519_import_private_raw

wc_curve25519_import_public()

int wc_curve25519_import_public	(	const byte *	in,
		word32	inLen,
		curve25519_key *	key
	)

This function imports a public key from the given in buffer and stores it in the curve25519_key structure.

Returns

0 Returned on successfully importing the public key into the curve25519_key structure.

ECC_BAD_ARG_E Returned if the inLen parameter does not match the key size of the key structure.

BAD_FUNC_ARG Returned if any of the input parameters are NULL.

Parameters

[in]	in	Pointer to the buffer containing the public key to import.
[in]	inLen	Length of the public key to import.
[in,out]	key	Pointer to the curve25519_key structure in which to store the key.

Example

int ret;
 
byte pub[32];
// initialize pub with public key
 
curve25519_key key;
// initialize key
 
ret = wc_curve25519_import_public(pub,sizeof(pub), &key);
if (ret != 0) {
    // error importing key
}

See also

wc_curve25519_init

wc_curve25519_export_public

wc_curve25519_import_private_raw

wc_curve25519_import_public_ex

wc_curve25519_check_public

wc_curve25519_size

wc_curve25519_import_public_ex()

int wc_curve25519_import_public_ex	(	const byte *	in,
		word32	inLen,
		curve25519_key *	key,
		int	endian
	)

This function imports a public key from the given in buffer and stores it in the curve25519_key structure.

Returns

0 Returned on successfully importing the public key into the curve25519_key structure.

ECC_BAD_ARG_E Returned if the inLen parameter does not match the key size of the key structure.

BAD_FUNC_ARG Returned if any of the input parameters are NULL.

Parameters

[in]	in	Pointer to the buffer containing the public key to import.
[in]	inLen	Length of the public key to import.
[in,out]	key	Pointer to the curve25519_key structure in which to store the key.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte pub[32];
// initialize pub with public key
curve25519_key key;
// initialize key
 
ret = wc_curve25519_import_public_ex(pub, sizeof(pub), &key,
        EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error importing key
}

See also

wc_curve25519_init

wc_curve25519_export_public

wc_curve25519_import_private_raw

wc_curve25519_import_public

wc_curve25519_check_public

wc_curve25519_size

wc_curve25519_init()

int wc_curve25519_init

(

curve25519_key *

key

)

This function initializes a Curve25519 key. It should be called before generating a key for the structure.

Returns

0 Returned on successfully initializing the curve25519_key structure.

BAD_FUNC_ARG Returned when key is NULL.

Parameters

[in,out]

key

Pointer to the curve25519_key structure to initialize.

Example

curve25519_key key;
wc_curve25519_init(&key); // initialize key
// make key and proceed to encryption

See also

wc_curve25519_make_key

wc_curve25519_make_key()

int wc_curve25519_make_key	(	WC_RNG *	rng,
		int	keysize,
		curve25519_key *	key
	)

This function generates a Curve25519 key using the given random number generator, rng, of the size given (keysize), and stores it in the given curve25519_key structure. It should be called after the key structure has been initialized through wc_curve25519_init().

Returns

0 Returned on successfully generating the key and and storing it in the given curve25519_key structure.

ECC_BAD_ARG_E Returned if the input keysize does not correspond to the keysize for a curve25519 key (32 bytes).

RNG_FAILURE_E Returned if the rng internal status is not DRBG_OK or if there is in generating the next random block with rng.

BAD_FUNC_ARG Returned if any of the input parameters passed in are NULL.

Parameters

[in]	rng	Pointer to the RNG object used to generate the ecc key.
[in]	keysize	Size of the key to generate. Must be 32 bytes for curve25519.
[in,out]	key	Pointer to the curve25519_key structure in which to store the generated key.

Example

int ret;
 
curve25519_key key;
wc_curve25519_init(&key); // initialize key
WC_RNG rng;
wc_InitRng(&rng); // initialize random number generator
 
ret = wc_curve25519_make_key(&rng, 32, &key);
if (ret != 0) {
    // error making Curve25519 key
}

See also

wc_curve25519_init

wc_curve25519_shared_secret()

int wc_curve25519_shared_secret	(	curve25519_key *	private_key,
		curve25519_key *	public_key,
		byte *	out,
		word32 *	outlen
	)

This function computes a shared secret key given a secret private key and a received public key. It stores the generated secret key in the buffer out and assigns the variable of the secret key to outlen. Only supports big endian.

Returns

0 Returned on successfully computing a shared secret key.

BAD_FUNC_ARG Returned if any of the input parameters passed in are NULL.

ECC_BAD_ARG_E Returned if the first bit of the public key is set, to avoid implementation fingerprinting.

Parameters

[in]	private_key	Pointer to the curve25519_key structure initialized with the user’s private key.
[in]	public_key	Pointer to the curve25519_key structure containing the received public key.
[out]	out	Pointer to a buffer in which to store the 32 byte computed secret key.
[in,out]	outlen	Pointer in which to store the length written to the output buffer.

Example

int ret;
 
byte sharedKey[32];
word32 keySz;
curve25519_key privKey, pubKey;
// initialize both keys
 
ret = wc_curve25519_shared_secret(&privKey, &pubKey, sharedKey, &keySz);
if (ret != 0) {
    // error generating shared key
}

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_shared_secret_ex

wc_curve25519_shared_secret_ex()

int wc_curve25519_shared_secret_ex	(	curve25519_key *	private_key,
		curve25519_key *	public_key,
		byte *	out,
		word32 *	outlen,
		int	endian
	)

This function computes a shared secret key given a secret private key and a received public key. It stores the generated secret key in the buffer out and assigns the variable of the secret key to outlen. Supports both big and little endian.

Returns

0 Returned on successfully computing a shared secret key.

BAD_FUNC_ARG Returned if any of the input parameters passed in are NULL.

ECC_BAD_ARG_E Returned if the first bit of the public key is set, to avoid implementation fingerprinting.

Parameters

[in]	private_key	Pointer to the curve25519_key structure initialized with the user’s private key.
[in]	public_key	Pointer to the curve25519_key structure containing the received public key.
[out]	out	Pointer to a buffer in which to store the 32 byte computed secret key.
	pin,out]	outlen Pointer in which to store the length written to the output buffer.
[in]	endian	EC25519_BIG_ENDIAN or EC25519_LITTLE_ENDIAN to set which form to use.

Example

int ret;
 
byte sharedKey[32];
word32 keySz;
 
curve25519_key privKey, pubKey;
// initialize both keys
 
ret = wc_curve25519_shared_secret_ex(&privKey, &pubKey, sharedKey, &keySz,
         EC25519_BIG_ENDIAN);
if (ret != 0) {
    // error generating shared key
}

See also

wc_curve25519_init

wc_curve25519_make_key

wc_curve25519_shared_secret

wc_curve25519_size()

int wc_curve25519_size

(

curve25519_key *

key

)

This function returns the key size of the given key structure.

Returns

Success Given a valid, initialized curve25519_key structure, returns the size of the key.

0 Returned if key is NULL

Parameters

[in]

key

Pointer to the curve25519_key structure in for which to determine the key size.

Example

int keySz;
 
curve25519_key key;
// initialize and make key
 
keySz = wc_curve25519_size(&key);

See also

wc_curve25519_init

wc_curve25519_make_key