hkdf.h File Reference

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Functions
ORDO_PUBLIC int	kdf_hkdf (prim_t hash, const void *params, const void *key, size_t key_len, const void *salt, size_t salt_len, const void *info, size_t info_len, void *out, size_t out_len)

Detailed Description

Module.

Module for the HMAC-based Extract-and-Expand Key Derivation Function. HKDF is a key stretching function which takes in a cryptographically secure key (not a password) and an optional salt, and generates a longer keystream deterministically.

Just like PBKDF2, HKDF does not require the use of contexts.

Function Documentation

ORDO_PUBLIC int kdf_hkdf	(	prim_t	hash,
		const void *	params,
		const void *	key,
		size_t	key_len,
		const void *	salt,
		size_t	salt_len,
		const void *	info,
		size_t	info_len,
		void *	out,
		size_t	out_len
	)

Derives a key using HKDF.

Parameters

[in]	hash	The hash function to use (the PRF used will be an instantiation of HMAC with it).
[in]	params	Hash-specific parameters.
[in]	key	The key to derive a keystream from.
[in]	key_len	The length in bytes of the key.
[in]	salt	The cryptographic salt to use.
[in]	salt_len	The length in bytes of the salt.
[in]	info	An application specific string.
[in]	info_len	The length in bytes of the info string.
[out]	out	The output buffer for the derived key.
[in]	out_len	The required length, in bytes, of the key.

Returns

ORDO_SUCCESS on success, else an error code.

Remarks

The salt may be zero-length in which case the buffer may be zero, and the info buffer may be zero-length as well.

The password or out buffers cannot be zero-length.

Warning

The HKDF algorithm distinguishes between zero-length salt, and no salt at all - thus, if you want to pass a zero-length salt (which is not recommended) pass a nonzero pointer with a zero length. If you want to pass no salt, pass a zero pointer with a zero length.

There is a maximum output length, of 255 multiplied by the digest length of the chosen hash function. This is by design.

Remarks

The out buffer should be at least out_len bytes long.