HKDF

Functions
int	mbedtls_hkdf (const mbedtls_md_info_t *md, const unsigned char *salt, size_t salt_len, const unsigned char *ikm, size_t ikm_len, const unsigned char *info, size_t info_len, unsigned char *okm, size_t okm_len)
	This is the HMAC-based Extract-and-Expand Key Derivation Function (HKDF). More...
int	mbedtls_hkdf_extract (const mbedtls_md_info_t *md, const unsigned char *salt, size_t salt_len, const unsigned char *ikm, size_t ikm_len, unsigned char *prk)
	Take the input keying material ikm and extract from it a fixed-length pseudorandom key prk. More...
int	mbedtls_hkdf_expand (const mbedtls_md_info_t *md, const unsigned char *prk, size_t prk_len, const unsigned char *info, size_t info_len, unsigned char *okm, size_t okm_len)
	Expand the supplied prk into several additional pseudorandom keys, which is the output of the HKDF. More...

HKDF Error codes
#define	MBEDTLS_ERR_HKDF_BAD_INPUT_DATA   -0x5F80
	Bad input parameters to function. More...

Detailed Description

Macro Definition Documentation

MBEDTLS_ERR_HKDF_BAD_INPUT_DATA

#define MBEDTLS_ERR_HKDF_BAD_INPUT_DATA   -0x5F80

Bad input parameters to function.

Definition at line 47 of file hkdf.h.

Function Documentation

mbedtls_hkdf()

int mbedtls_hkdf	(	const mbedtls_md_info_t *	md,
		const unsigned char *	salt,
		size_t	salt_len,
		const unsigned char *	ikm,
		size_t	ikm_len,
		const unsigned char *	info,
		size_t	info_len,
		unsigned char *	okm,
		size_t	okm_len
	)

This is the HMAC-based Extract-and-Expand Key Derivation Function (HKDF).

Parameters

md	A hash function; md.size denotes the length of the hash function output in bytes.
salt	An optional salt value (a non-secret random value); if the salt is not provided, a string of all zeros of md.size length is used as the salt.
salt_len	The length in bytes of the optional salt.
ikm	The input keying material.
ikm_len	The length in bytes of ikm.
info	An optional context and application specific information string. This can be a zero-length string.
info_len	The length of info in bytes.
okm	The output keying material of okm_len bytes.
okm_len	The length of the output keying material in bytes. This must be less than or equal to 255 * md.size bytes.

Returns

0 on success.

MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid.

An MBEDTLS_ERR_MD_* error for errors returned from the underlying MD layer.

mbedtls_hkdf_extract()

int mbedtls_hkdf_extract	(	const mbedtls_md_info_t *	md,
		const unsigned char *	salt,
		size_t	salt_len,
		const unsigned char *	ikm,
		size_t	ikm_len,
		unsigned char *	prk
	)

Take the input keying material ikm and extract from it a fixed-length pseudorandom key prk.

Warning

This function should only be used if the security of it has been studied and established in that particular context (eg. TLS 1.3 key schedule). For standard HKDF security guarantees use mbedtls_hkdf instead.

Parameters

	md	A hash function; md.size denotes the length of the hash function output in bytes.
	salt	An optional salt value (a non-secret random value); if the salt is not provided, a string of all zeros of md.size length is used as the salt.
	salt_len	The length in bytes of the optional salt.
	ikm	The input keying material.
	ikm_len	The length in bytes of ikm.
[out]	prk	A pseudorandom key of at least md.size bytes.

Returns

0 on success.

MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid.

An MBEDTLS_ERR_MD_* error for errors returned from the underlying MD layer.

mbedtls_hkdf_expand()

int mbedtls_hkdf_expand	(	const mbedtls_md_info_t *	md,
		const unsigned char *	prk,
		size_t	prk_len,
		const unsigned char *	info,
		size_t	info_len,
		unsigned char *	okm,
		size_t	okm_len
	)

Expand the supplied prk into several additional pseudorandom keys, which is the output of the HKDF.

Warning

This function should only be used if the security of it has been studied and established in that particular context (eg. TLS 1.3 key schedule). For standard HKDF security guarantees use mbedtls_hkdf instead.

Parameters

md	A hash function; md.size denotes the length of the hash function output in bytes.
prk	A pseudorandom key of at least md.size bytes. prk is usually the output from the HKDF extract step.
prk_len	The length in bytes of prk.
info	An optional context and application specific information string. This can be a zero-length string.
info_len	The length of info in bytes.
okm	The output keying material of okm_len bytes.
okm_len	The length of the output keying material in bytes. This must be less than or equal to 255 * md.size bytes.

Returns

0 on success.

MBEDTLS_ERR_HKDF_BAD_INPUT_DATA when the parameters are invalid.

An MBEDTLS_ERR_MD_* error for errors returned from the underlying MD layer.