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ecdh.h File Reference

This file contains ECDH definitions and functions. More...

`#include "mbedtls/private_access.h"`
`#include "mbedtls/build_info.h"`
`#include "mbedtls/ecp.h"`
Include dependency graph for ecdh.h:
This graph shows which files directly or indirectly include this file:

Go to the source code of this file.

## Data Structures

struct | mbedtls_ecdh_context_mbed
struct | mbedtls_ecdh_context
| The ECDH context structure. More...

## Typedefs

typedef struct mbedtls_ecdh_context_mbed | mbedtls_ecdh_context_mbed
typedef struct mbedtls_ecdh_context | mbedtls_ecdh_context
| The ECDH context structure.

## Enumerations

enum | mbedtls_ecdh_side { MBEDTLS_ECDH_OURS , MBEDTLS_ECDH_THEIRS }
enum | mbedtls_ecdh_variant { MBEDTLS_ECDH_VARIANT_NONE = 0 , MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0 }

## Functions

mbedtls_ecp_group_id | mbedtls_ecdh_get_grp_id (mbedtls_ecdh_context *ctx)
| Return the ECP group for provided context.
int | mbedtls_ecdh_can_do (mbedtls_ecp_group_id gid)
| Check whether a given group can be used for ECDH.
int | mbedtls_ecdh_gen_public (mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function generates an ECDH keypair on an elliptic curve.
int | mbedtls_ecdh_compute_shared (mbedtls_ecp_group *grp, mbedtls_mpi *z, const mbedtls_ecp_point *Q, const mbedtls_mpi *d, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function computes the shared secret.
void | mbedtls_ecdh_init (mbedtls_ecdh_context *ctx)
| This function initializes an ECDH context.
int | mbedtls_ecdh_setup (mbedtls_ecdh_context *ctx, mbedtls_ecp_group_id grp_id)
| This function sets up the ECDH context with the information given.
void | mbedtls_ecdh_free (mbedtls_ecdh_context *ctx)
| This function frees a context.
int | mbedtls_ecdh_make_params (mbedtls_ecdh_context *ctx, size_t *olen, unsigned char *buf, size_t blen, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function generates an EC key pair and exports its in the format used in a TLS ServerKeyExchange handshake message.
int | mbedtls_ecdh_read_params (mbedtls_ecdh_context *ctx, const unsigned char **buf, const unsigned char *end)
| This function parses the ECDHE parameters in a TLS ServerKeyExchange handshake message.
int | mbedtls_ecdh_get_params (mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key, mbedtls_ecdh_side side)
| This function sets up an ECDH context from an EC key.
int | mbedtls_ecdh_make_public (mbedtls_ecdh_context *ctx, size_t *olen, unsigned char *buf, size_t blen, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function generates a public key and exports it as a TLS ClientKeyExchange payload.
int | mbedtls_ecdh_read_public (mbedtls_ecdh_context *ctx, const unsigned char *buf, size_t blen)
| This function parses and processes the ECDHE payload of a TLS ClientKeyExchange message.
int | mbedtls_ecdh_calc_secret (mbedtls_ecdh_context *ctx, size_t *olen, unsigned char *buf, size_t blen, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function derives and exports the shared secret.

## Detailed Description

This file contains ECDH definitions and functions.

The Elliptic Curve Diffie-Hellman (ECDH) protocol is an anonymous key agreement protocol allowing two parties to establish a shared secret over an insecure channel. Each party must have an elliptic-curve public–private key pair.

For more information, see NIST SP 800-56A Rev. 2: Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography.

Definition in file ecdh.h.

## Typedef Documentation

## mbedtls_ecdh_context

typedef struct mbedtls_ecdh_context mbedtls_ecdh_context

The ECDH context structure.

Warning
  Performing multiple operations concurrently on the same ECDSA context is not supported; objects of this type should not be shared between multiple threads.

## mbedtls_ecdh_context_mbed

typedef struct mbedtls_ecdh_context_mbed mbedtls_ecdh_context_mbed

The context used by the default ECDH implementation.

Later versions might change the structure of this context, therefore users should not make any assumptions about the structure of mbedtls_ecdh_context_mbed.

## Enumeration Type Documentation

## mbedtls_ecdh_side

enum mbedtls_ecdh_side

Defines the source of the imported EC key.

Enumerator
MBEDTLS_ECDH_OURS | Our key.
MBEDTLS_ECDH_THEIRS | The key of the peer.

Definition at line 59 of file ecdh.h.

## mbedtls_ecdh_variant

enum mbedtls_ecdh_variant

Defines the ECDH implementation used.

Later versions of the library may add new variants, therefore users should not make any assumptions about them.

Enumerator
MBEDTLS_ECDH_VARIANT_NONE | Implementation not defined.
MBEDTLS_ECDH_VARIANT_MBEDTLS_2_0 | The default Mbed TLS implementation

Definition at line 71 of file ecdh.h.

## Function Documentation

## mbedtls_ecdh_calc_secret()

int mbedtls_ecdh_calc_secret | ( | mbedtls_ecdh_context * | ctx,
|  | size_t * | olen,
|  | unsigned char * | buf,
|  | size_t | blen,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function derives and exports the shared secret.

                 This is the last function used by both TLS client
                 and servers.

Note
  If `f_rng` is not NULL, it is used to implement countermeasures against side-channel attacks. For more information, see mbedtls_ecp_mul().

See also
  ecp.h

Parameters

  ctx | The ECDH context to use. This must be initialized and have its own private key generated and the peer's public key imported.
  olen | The address at which to store the total number of Bytes written on success. This must not be `NULL`.
  buf | The buffer to write the generated shared key to. This must be a writable buffer of size `blen` Bytes.
  blen | The length of the destination buffer `buf` in Bytes.
  f_rng | The RNG function to use. This must not be `NULL`.
  p_rng | The RNG context. This may be `NULL` if `f_rng` doesn't need a context argument.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see `mbedtls_ecp_set_max_ops()`.
  Another `MBEDTLS_ERR_ECP_XXX` error code on failure.

## mbedtls_ecdh_can_do()

int mbedtls_ecdh_can_do | ( | mbedtls_ecp_group_id | gid | ) |

Check whether a given group can be used for ECDH.

Parameters

  gid | The ECP group ID to check.

Returns
  `1` if the group can be used, `0` otherwise

## mbedtls_ecdh_compute_shared()

int mbedtls_ecdh_compute_shared | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_mpi * | z,
|  | const mbedtls_ecp_point * | Q,
|  | const mbedtls_mpi * | d,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function computes the shared secret.

                 This function performs the second of two core computations
                 implemented during the ECDH key exchange. The first core
                 computation is performed by mbedtls_ecdh_gen_public().

See also
  ecp.h

Note
  If `f_rng` is not NULL, it is used to implement countermeasures against side-channel attacks. For more information, see mbedtls_ecp_mul().

Parameters

  grp | The ECP group to use. This must be initialized and have domain parameters loaded, for example through mbedtls_ecp_load() or mbedtls_ecp_tls_read_group().
  z | The destination MPI (shared secret). This must be initialized.
  Q | The public key from another party. This must be initialized.
  d | Our secret exponent (private key). This must be initialized.
  f_rng | The RNG function to use. This must not be `NULL`.
  p_rng | The RNG context to be passed to `f_rng`. This may be `NULL` if `f_rng` is `NULL` or doesn't need a context argument.

Returns
  `0` on success.
  Another `MBEDTLS_ERR_ECP_XXX` or `MBEDTLS_MPI_XXX` error code on failure.

## mbedtls_ecdh_free()

void mbedtls_ecdh_free | ( | mbedtls_ecdh_context * | ctx | ) |

This function frees a context.

Parameters

  ctx | The context to free. This may be `NULL`, in which case this function does nothing. If it is not `NULL`, it must point to an initialized ECDH context.

## mbedtls_ecdh_gen_public()

int mbedtls_ecdh_gen_public | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_mpi * | d,
|  | mbedtls_ecp_point * | Q,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function generates an ECDH keypair on an elliptic curve.

This function performs the first of two core computations implemented during the ECDH key exchange. The second core computation is performed by mbedtls_ecdh_compute_shared().

See also
  ecp.h

Parameters

  grp | The ECP group to use. This must be initialized and have domain parameters loaded, for example through mbedtls_ecp_load() or mbedtls_ecp_tls_read_group().
  d | The destination MPI (private key). This must be initialized.
  Q | The destination point (public key). This must be initialized.
  f_rng | The RNG function to use. This must not be `NULL`.
  p_rng | The RNG context to be passed to `f_rng`. This may be `NULL` in case `f_rng` doesn't need a context argument.

Returns
  `0` on success.
  Another `MBEDTLS_ERR_ECP_XXX` or `MBEDTLS_MPI_XXX` error code on failure.

## mbedtls_ecdh_get_grp_id()

mbedtls_ecp_group_id mbedtls_ecdh_get_grp_id | ( | mbedtls_ecdh_context * | ctx | ) |

Return the ECP group for provided context.

Note
  To access group specific fields, users should use `mbedtls_ecp_curve_info_from_grp_id` or `mbedtls_ecp_group_load` on the extracted `group_id`.

Parameters

  ctx | The ECDH context to parse. This must not be `NULL`.

Returns
  The `mbedtls_ecp_group_id` of the context.

## mbedtls_ecdh_get_params()

int mbedtls_ecdh_get_params | ( | mbedtls_ecdh_context * | ctx,
|  | const mbedtls_ecp_keypair * | key,
|  | mbedtls_ecdh_side | side
| ) |  |

This function sets up an ECDH context from an EC key.

                 It is used by clients and servers in place of the
                 ServerKeyExchange for static ECDH, and imports ECDH
                 parameters from the EC key information of a certificate.

See also
  ecp.h

Parameters

  ctx | The ECDH context to set up. This must be initialized.
  key | The EC key to use. This must be initialized.

  side

  Defines the source of the key. Possible values are:
  - MBEDTLS_ECDH_OURS: The key is ours.
  - MBEDTLS_ECDH_THEIRS: The key is that of the peer.

Returns
  `0` on success.
  Another `MBEDTLS_ERR_ECP_XXX` error code on failure.

## mbedtls_ecdh_init()

void mbedtls_ecdh_init | ( | mbedtls_ecdh_context * | ctx | ) |

This function initializes an ECDH context.

Parameters

  ctx | The ECDH context to initialize. This must not be `NULL`.

## mbedtls_ecdh_make_params()

int mbedtls_ecdh_make_params | ( | mbedtls_ecdh_context * | ctx,
|  | size_t * | olen,
|  | unsigned char * | buf,
|  | size_t | blen,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function generates an EC key pair and exports its in the format used in a TLS ServerKeyExchange handshake message.

This is the second function used by a TLS server for ECDHE ciphersuites. (It is called after mbedtls_ecdh_setup().)

See also
  ecp.h

Parameters

  ctx | The ECDH context to use. This must be initialized and bound to a group, for example via mbedtls_ecdh_setup().
  olen | The address at which to store the number of Bytes written.
  buf | The destination buffer. This must be a writable buffer of length `blen` Bytes.
  blen | The length of the destination buffer `buf` in Bytes.
  f_rng | The RNG function to use. This must not be `NULL`.
  p_rng | The RNG context to be passed to `f_rng`. This may be `NULL` in case `f_rng` doesn't need a context argument.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see `mbedtls_ecp_set_max_ops()`.
  Another `MBEDTLS_ERR_ECP_XXX` error code on failure.

## mbedtls_ecdh_make_public()

int mbedtls_ecdh_make_public | ( | mbedtls_ecdh_context * | ctx,
|  | size_t * | olen,
|  | unsigned char * | buf,
|  | size_t | blen,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function generates a public key and exports it as a TLS ClientKeyExchange payload.

This is the second function used by a TLS client for ECDH(E) ciphersuites.

See also
  ecp.h

Parameters

  ctx | The ECDH context to use. This must be initialized and bound to a group, the latter usually by mbedtls_ecdh_read_params().
  olen | The address at which to store the number of Bytes written. This must not be `NULL`.
  buf | The destination buffer. This must be a writable buffer of length `blen` Bytes.
  blen | The size of the destination buffer `buf` in Bytes.
  f_rng | The RNG function to use. This must not be `NULL`.
  p_rng | The RNG context to be passed to `f_rng`. This may be `NULL` in case `f_rng` doesn't need a context argument.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see `mbedtls_ecp_set_max_ops()`.
  Another `MBEDTLS_ERR_ECP_XXX` error code on failure.

## mbedtls_ecdh_read_params()

int mbedtls_ecdh_read_params | ( | mbedtls_ecdh_context * | ctx,
|  | const unsigned char ** | buf,
|  | const unsigned char * | end
| ) |  |

This function parses the ECDHE parameters in a TLS ServerKeyExchange handshake message.

Note
  In a TLS handshake, this is the how the client sets up its ECDHE context from the server's public ECDHE key material.

See also
  ecp.h

Parameters

  ctx | The ECDHE context to use. This must be initialized.
  buf | On input, `*buf` must be the start of the input buffer. On output, `*buf` is updated to point to the end of the data that has been read. On success, this is the first byte past the end of the ServerKeyExchange parameters. On error, this is the point at which an error has been detected, which is usually not useful except to debug failures.
  end | The end of the input buffer.

Returns
  `0` on success.
  An `MBEDTLS_ERR_ECP_XXX` error code on failure.

## mbedtls_ecdh_read_public()

int mbedtls_ecdh_read_public | ( | mbedtls_ecdh_context * | ctx,
|  | const unsigned char * | buf,
|  | size_t | blen
| ) |  |

This function parses and processes the ECDHE payload of a TLS ClientKeyExchange message.

This is the third function used by a TLS server for ECDH(E) ciphersuites. (It is called after mbedtls_ecdh_setup() and mbedtls_ecdh_make_params().)

See also
  ecp.h

Parameters

  ctx | The ECDH context to use. This must be initialized and bound to a group, for example via mbedtls_ecdh_setup().
  buf | The pointer to the ClientKeyExchange payload. This must be a readable buffer of length `blen` Bytes.
  blen | The length of the input buffer `buf` in Bytes.

Returns
  `0` on success.
  An `MBEDTLS_ERR_ECP_XXX` error code on failure.

## mbedtls_ecdh_setup()

int mbedtls_ecdh_setup | ( | mbedtls_ecdh_context * | ctx,
|  | mbedtls_ecp_group_id | grp_id
| ) |  |

This function sets up the ECDH context with the information given.

This function should be called after mbedtls_ecdh_init() but before mbedtls_ecdh_make_params(). There is no need to call this function before mbedtls_ecdh_read_params().

This is the first function used by a TLS server for ECDHE ciphersuites.

Parameters

  ctx | The ECDH context to set up. This must be initialized.
  grp_id | The group id of the group to set up the context for.

Returns
  `0` on success.