KDF#

Key derivation functions (KDFs) are used to derive cryptographically strong keys from an initial secret value.

HKDF#

HMAC-based Extract-and-Expand Key Derivation Function (HKDF) RFC 5869.

Similar to RFC 5869, the following descriptions uses the term HashLen to denote the output length of the hash function of a concrete instantiation of HKDF.

The following instantiations are supported:

  • BLAKE2b (HashLen = 64)

  • BLAKE2s (HashLen = 32)

  • SHA2-256 (HashLen = 32)

  • SHA2-512 (HashLen = 64)

API Reference#

BLAKE2b#

#include "Hacl_HKDF.h"
void Hacl_HKDF_extract_blake2b_32(uint8_t *prk, uint8_t *salt, uint32_t saltlen, uint8_t *ikm, uint32_t ikmlen)#

Extract a fixed-length pseudorandom key from input keying material.

Parameters

  • prk – Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt – Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen – Length of salt value.

  • ikm – Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen – Length of input keying material.

Extract a fixed-length pseudorandom key from input keying material.

  • prk Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen Length of salt value.

  • ikm Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen Length of input keying material.

#include "Hacl_HKDF.h"
void Hacl_HKDF_expand_blake2b_32(uint8_t *okm, uint8_t *prk, uint32_t prklen, uint8_t *info, uint32_t infolen, uint32_t len)#

Expand pseudorandom key to desired length.

Parameters

  • okm – Pointer to len bytes of memory where output keying material is written to.

  • prk – Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen – Length of pseudorandom key.

  • info – Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen – Length of context and application specific information.

  • len – Length of output keying material.

Expand pseudorandom key to desired length.

  • okm Pointer to len bytes of memory where output keying material is written to.

  • prk Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen Length of pseudorandom key.

  • info Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen Length of context and application specific information.

  • len Length of output keying material.

BLAKE2s#

#include "Hacl_HKDF.h"
void Hacl_HKDF_extract_blake2s_32(uint8_t *prk, uint8_t *salt, uint32_t saltlen, uint8_t *ikm, uint32_t ikmlen)#

Extract a fixed-length pseudorandom key from input keying material.

Parameters

  • prk – Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt – Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen – Length of salt value.

  • ikm – Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen – Length of input keying material.

Extract a fixed-length pseudorandom key from input keying material.

  • prk Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen Length of salt value.

  • ikm Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen Length of input keying material.

#include "Hacl_HKDF.h"
void Hacl_HKDF_expand_blake2s_32(uint8_t *okm, uint8_t *prk, uint32_t prklen, uint8_t *info, uint32_t infolen, uint32_t len)#

Expand pseudorandom key to desired length.

Parameters

  • okm – Pointer to len bytes of memory where output keying material is written to.

  • prk – Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen – Length of pseudorandom key.

  • info – Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen – Length of context and application specific information.

  • len – Length of output keying material.

Expand pseudorandom key to desired length.

  • okm Pointer to len bytes of memory where output keying material is written to.

  • prk Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen Length of pseudorandom key.

  • info Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen Length of context and application specific information.

  • len Length of output keying material.

SHA2-256#

#include "Hacl_HKDF.h"
void Hacl_HKDF_extract_sha2_256(uint8_t *prk, uint8_t *salt, uint32_t saltlen, uint8_t *ikm, uint32_t ikmlen)#

Extract a fixed-length pseudorandom key from input keying material.

Parameters

  • prk – Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt – Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen – Length of salt value.

  • ikm – Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen – Length of input keying material.

Extract a fixed-length pseudorandom key from input keying material.

  • prk Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen Length of salt value.

  • ikm Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen Length of input keying material.

void Hacl_HKDF_expand_sha2_256(uint8_t *okm, uint8_t *prk, uint32_t prklen, uint8_t *info, uint32_t infolen, uint32_t len)#

Expand pseudorandom key to desired length.

Parameters

  • okm – Pointer to len bytes of memory where output keying material is written to.

  • prk – Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen – Length of pseudorandom key.

  • info – Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen – Length of context and application specific information.

  • len – Length of output keying material.

Expand pseudorandom key to desired length.

  • okm Pointer to len bytes of memory where output keying material is written to.

  • prk Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen Length of pseudorandom key.

  • info Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen Length of context and application specific information.

  • len Length of output keying material.

SHA2-512#

#include "Hacl_HKDF.h"
void Hacl_HKDF_extract_sha2_512(uint8_t *prk, uint8_t *salt, uint32_t saltlen, uint8_t *ikm, uint32_t ikmlen)#

Extract a fixed-length pseudorandom key from input keying material.

Parameters

  • prk – Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt – Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen – Length of salt value.

  • ikm – Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen – Length of input keying material.

Extract a fixed-length pseudorandom key from input keying material.

  • prk Pointer to HashLen bytes of memory where pseudorandom key is written to.

  • salt Pointer to saltlen bytes of memory where salt value is read from.

  • saltlen Length of salt value.

  • ikm Pointer to ikmlen bytes of memory where input keying material is read from.

  • ikmlen Length of input keying material.

void Hacl_HKDF_expand_sha2_512(uint8_t *okm, uint8_t *prk, uint32_t prklen, uint8_t *info, uint32_t infolen, uint32_t len)#

Expand pseudorandom key to desired length.

Parameters

  • okm – Pointer to len bytes of memory where output keying material is written to.

  • prk – Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen – Length of pseudorandom key.

  • info – Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen – Length of context and application specific information.

  • len – Length of output keying material.

Expand pseudorandom key to desired length.

  • okm Pointer to len bytes of memory where output keying material is written to.

  • prk Pointer to at least HashLen bytes of memory where pseudorandom key is read from. Usually, this points to the output from the extract step.

  • prklen Length of pseudorandom key.

  • info Pointer to infolen bytes of memory where context and application specific information is read from. Can be a zero-length string.

  • infolen Length of context and application specific information.

  • len Length of output keying material.