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hkdf.h File Reference

This file contains the HKDF interface. More...

`#include "mbedtls/config.h"`
`#include "mbedtls/md.h"`
Include dependency graph for hkdf.h:

Go to the source code of this file.

## Macros

HKDF Error codes
#define | MBEDTLS_ERR_HKDF_BAD_INPUT_DATA -0x5F80

## 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).
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`.
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.

## Detailed Description

This file contains the HKDF interface.

         The HMAC-based Extract-and-Expand Key Derivation Function (HKDF) is
         specified by RFC 5869.

Definition in file hkdf.h.

## 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 29 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_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.

## 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.