mbed TLS v2.23.0

Data Structures | Macros | Typedefs | Enumerations
ecp.h File Reference

This file provides an API for Elliptic Curves over GF(P) (ECP). More...

`#include "mbedtls/config.h"`
`#include "mbedtls/bignum.h"`
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## Data Structures
struct | mbedtls_ecp_curve_info
struct | mbedtls_ecp_point
| The ECP point structure, in Jacobian coordinates. More...
struct | mbedtls_ecp_group
| The ECP group structure. More...
struct | mbedtls_ecp_keypair
| The ECP key-pair structure. More...

## Macros
#define | MBEDTLS_ERR_ECP_BAD_INPUT_DATA -0x4F80
#define | MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL -0x4F00
#define | MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE -0x4E80
#define | MBEDTLS_ERR_ECP_VERIFY_FAILED -0x4E00
#define | MBEDTLS_ERR_ECP_ALLOC_FAILED -0x4D80
#define | MBEDTLS_ERR_ECP_RANDOM_FAILED -0x4D00
#define | MBEDTLS_ERR_ECP_INVALID_KEY -0x4C80
#define | MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH -0x4C00
#define | MBEDTLS_ERR_ECP_HW_ACCEL_FAILED -0x4B80
#define | MBEDTLS_ERR_ECP_IN_PROGRESS -0x4B00
#define | MBEDTLS_ECP_DP_MAX 12

## Typedefs
typedef struct mbedtls_ecp_curve_info | mbedtls_ecp_curve_info
typedef struct mbedtls_ecp_point | mbedtls_ecp_point
| The ECP point structure, in Jacobian coordinates. More...
typedef struct mbedtls_ecp_group | mbedtls_ecp_group
| The ECP group structure. More...

## Enumerations
enum | mbedtls_ecp_group_id { MBEDTLS_ECP_DP_NONE = 0, MBEDTLS_ECP_DP_SECP192R1, MBEDTLS_ECP_DP_SECP224R1, MBEDTLS_ECP_DP_SECP256R1, MBEDTLS_ECP_DP_SECP384R1, MBEDTLS_ECP_DP_SECP521R1, MBEDTLS_ECP_DP_BP256R1, MBEDTLS_ECP_DP_BP384R1, MBEDTLS_ECP_DP_BP512R1, MBEDTLS_ECP_DP_CURVE25519, MBEDTLS_ECP_DP_SECP192K1, MBEDTLS_ECP_DP_SECP224K1, MBEDTLS_ECP_DP_SECP256K1, MBEDTLS_ECP_DP_CURVE448 }
enum | mbedtls_ecp_curve_type { MBEDTLS_ECP_TYPE_NONE = 0, MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS, MBEDTLS_ECP_TYPE_MONTGOMERY }

## SECTION: Module settings
The configuration options you can set for this module are in this section. Either change them in config.h, or define them using the compiler command line.
#define | MBEDTLS_ECP_MAX_BITS 521
#define | MBEDTLS_ECP_MAX_BYTES ( ( MBEDTLS_ECP_MAX_BITS + 7 ) / 8 )
#define | MBEDTLS_ECP_MAX_PT_LEN ( 2 * MBEDTLS_ECP_MAX_BYTES + 1 )
#define | MBEDTLS_ECP_WINDOW_SIZE 6
#define | MBEDTLS_ECP_FIXED_POINT_OPTIM 1
#define | MBEDTLS_ECP_BUDGET(ops) /* no-op; for compatibility */
#define | MBEDTLS_ECP_PF_UNCOMPRESSED 0
#define | MBEDTLS_ECP_PF_COMPRESSED 1
#define | MBEDTLS_ECP_TLS_NAMED_CURVE 3
typedef void | mbedtls_ecp_restart_ctx
typedef struct mbedtls_ecp_keypair | mbedtls_ecp_keypair
| The ECP key-pair structure. More...
mbedtls_ecp_curve_type | mbedtls_ecp_get_type (const mbedtls_ecp_group *grp)
const mbedtls_ecp_curve_info * | mbedtls_ecp_curve_list (void)
| This function retrieves the information defined in mbedtls_ecp_curve_info() for all supported curves in order of preference. More...
const mbedtls_ecp_group_id * | mbedtls_ecp_grp_id_list (void)
| This function retrieves the list of internal group identifiers of all supported curves in the order of preference. More...
const mbedtls_ecp_curve_info * | mbedtls_ecp_curve_info_from_grp_id (mbedtls_ecp_group_id grp_id)
| This function retrieves curve information from an internal group identifier. More...
const mbedtls_ecp_curve_info * | mbedtls_ecp_curve_info_from_tls_id (uint16_t tls_id)
| This function retrieves curve information from a TLS NamedCurve value. More...
const mbedtls_ecp_curve_info * | mbedtls_ecp_curve_info_from_name (const char *name)
| This function retrieves curve information from a human-readable name. More...
void | mbedtls_ecp_point_init (mbedtls_ecp_point *pt)
| This function initializes a point as zero. More...
void | mbedtls_ecp_group_init (mbedtls_ecp_group *grp)
| This function initializes an ECP group context without loading any domain parameters. More...
void | mbedtls_ecp_keypair_init (mbedtls_ecp_keypair *key)
| This function initializes a key pair as an invalid one. More...
void | mbedtls_ecp_point_free (mbedtls_ecp_point *pt)
| This function frees the components of a point. More...
void | mbedtls_ecp_group_free (mbedtls_ecp_group *grp)
| This function frees the components of an ECP group. More...
void | mbedtls_ecp_keypair_free (mbedtls_ecp_keypair *key)
| This function frees the components of a key pair. More...
int | mbedtls_ecp_copy (mbedtls_ecp_point *P, const mbedtls_ecp_point *Q)
| This function copies the contents of point `Q` into point `P`. More...
int | mbedtls_ecp_group_copy (mbedtls_ecp_group *dst, const mbedtls_ecp_group *src)
| This function copies the contents of group `src` into group `dst`. More...
int | mbedtls_ecp_set_zero (mbedtls_ecp_point *pt)
| This function sets a point to the point at infinity. More...
int | mbedtls_ecp_is_zero (mbedtls_ecp_point *pt)
| This function checks if a point is the point at infinity. More...
int | mbedtls_ecp_point_cmp (const mbedtls_ecp_point *P, const mbedtls_ecp_point *Q)
| This function compares two points. More...
int | mbedtls_ecp_point_read_string (mbedtls_ecp_point *P, int radix, const char *x, const char *y)
| This function imports a non-zero point from two ASCII strings. More...
int | mbedtls_ecp_point_write_binary (const mbedtls_ecp_group *grp, const mbedtls_ecp_point *P, int format, size_t *olen, unsigned char *buf, size_t buflen)
| This function exports a point into unsigned binary data. More...
int | mbedtls_ecp_point_read_binary (const mbedtls_ecp_group *grp, mbedtls_ecp_point *P, const unsigned char *buf, size_t ilen)
| This function imports a point from unsigned binary data. More...
int | mbedtls_ecp_tls_read_point (const mbedtls_ecp_group *grp, mbedtls_ecp_point *pt, const unsigned char **buf, size_t len)
| This function imports a point from a TLS ECPoint record. More...
int | mbedtls_ecp_tls_write_point (const mbedtls_ecp_group *grp, const mbedtls_ecp_point *pt, int format, size_t *olen, unsigned char *buf, size_t blen)
| This function exports a point as a TLS ECPoint record defined in RFC 4492, Section 5.4. More...
int | mbedtls_ecp_group_load (mbedtls_ecp_group *grp, mbedtls_ecp_group_id id)
| This function sets up an ECP group context from a standardized set of domain parameters. More...
int | mbedtls_ecp_tls_read_group (mbedtls_ecp_group *grp, const unsigned char **buf, size_t len)
| This function sets up an ECP group context from a TLS ECParameters record as defined in RFC 4492, Section 5.4. More...
int | mbedtls_ecp_tls_read_group_id (mbedtls_ecp_group_id *grp, const unsigned char **buf, size_t len)
| This function extracts an elliptic curve group ID from a TLS ECParameters record as defined in RFC 4492, Section 5.4. More...
int | mbedtls_ecp_tls_write_group (const mbedtls_ecp_group *grp, size_t *olen, unsigned char *buf, size_t blen)
| This function exports an elliptic curve as a TLS ECParameters record as defined in RFC 4492, Section 5.4. More...
int | mbedtls_ecp_mul (mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function performs a scalar multiplication of a point by an integer: `R` = `m` * `P`. More...
int | mbedtls_ecp_mul_restartable (mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng, mbedtls_ecp_restart_ctx *rs_ctx)
| This function performs multiplication of a point by an integer: `R` = `m` * `P` in a restartable way. More...
int | mbedtls_ecp_muladd (mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, const mbedtls_mpi *n, const mbedtls_ecp_point *Q)
| This function performs multiplication and addition of two points by integers: `R` = `m` * `P` + `n` * `Q`. More...
int | mbedtls_ecp_muladd_restartable (mbedtls_ecp_group *grp, mbedtls_ecp_point *R, const mbedtls_mpi *m, const mbedtls_ecp_point *P, const mbedtls_mpi *n, const mbedtls_ecp_point *Q, mbedtls_ecp_restart_ctx *rs_ctx)
| This function performs multiplication and addition of two points by integers: `R` = `m` * `P` + `n` * `Q` in a restartable way. More...
int | mbedtls_ecp_check_pubkey (const mbedtls_ecp_group *grp, const mbedtls_ecp_point *pt)
| This function checks that a point is a valid public key on this curve. More...
int | mbedtls_ecp_check_privkey (const mbedtls_ecp_group *grp, const mbedtls_mpi *d)
| This function checks that an `mbedtls_mpi` is a valid private key for this curve. More...
int | mbedtls_ecp_gen_privkey (const mbedtls_ecp_group *grp, mbedtls_mpi *d, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function generates a private key. More...
int | mbedtls_ecp_gen_keypair_base (mbedtls_ecp_group *grp, const mbedtls_ecp_point *G, mbedtls_mpi *d, mbedtls_ecp_point *Q, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function generates a keypair with a configurable base point. More...
int | mbedtls_ecp_gen_keypair (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 ECP keypair. More...
int | mbedtls_ecp_gen_key (mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key, int(*f_rng)(void *, unsigned char *, size_t), void *p_rng)
| This function generates an ECP key. More...
int | mbedtls_ecp_read_key (mbedtls_ecp_group_id grp_id, mbedtls_ecp_keypair *key, const unsigned char *buf, size_t buflen)
| This function reads an elliptic curve private key. More...
int | mbedtls_ecp_check_pub_priv (const mbedtls_ecp_keypair *pub, const mbedtls_ecp_keypair *prv)
| This function checks that the keypair objects `pub` and `prv` have the same group and the same public point, and that the private key in `prv` is consistent with the public key. More...
int | mbedtls_ecp_self_test (int verbose)
| The ECP checkup routine. More...

## Detailed Description

This file provides an API for Elliptic Curves over GF(P) (ECP).

The use of ECP in cryptography and TLS is defined in Standards for Efficient Cryptography Group (SECG): SEC1 Elliptic Curve Cryptography and RFC-4492: Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS).

RFC-2409: The Internet Key Exchange (IKE) defines ECP group types.

Definition in file ecp.h.

## Macro Definition Documentation

## ◆ MBEDTLS_ECP_BUDGET

#define MBEDTLS_ECP_BUDGET | ( |  | ops | ) | /* no-op; for compatibility */

Definition at line 328 of file ecp.h.

## ◆ MBEDTLS_ECP_DP_MAX

#define MBEDTLS_ECP_DP_MAX 12

The number of supported curves, plus one for MBEDTLS_ECP_DP_NONE.

Note
  Montgomery curves are currently excluded.

Definition at line 101 of file ecp.h.

## ◆ MBEDTLS_ECP_FIXED_POINT_OPTIM

#define MBEDTLS_ECP_FIXED_POINT_OPTIM 1

Enable fixed-point speed-up.

Definition at line 262 of file ecp.h.

## ◆ MBEDTLS_ECP_MAX_BITS

#define MBEDTLS_ECP_MAX_BITS 521

The maximum size of the groups, that is, of `N` and `P`. The maximum size of groups, in bits.

Definition at line 221 of file ecp.h.

## ◆ MBEDTLS_ECP_MAX_BYTES

#define MBEDTLS_ECP_MAX_BYTES ( ( MBEDTLS_ECP_MAX_BITS + 7 ) / 8 )

Definition at line 224 of file ecp.h.

## ◆ MBEDTLS_ECP_MAX_PT_LEN

#define MBEDTLS_ECP_MAX_PT_LEN ( 2 * MBEDTLS_ECP_MAX_BYTES + 1 )

Definition at line 225 of file ecp.h.

## ◆ MBEDTLS_ECP_PF_COMPRESSED

#define MBEDTLS_ECP_PF_COMPRESSED 1

Compressed point format.

Definition at line 355 of file ecp.h.

## ◆ MBEDTLS_ECP_PF_UNCOMPRESSED

#define MBEDTLS_ECP_PF_UNCOMPRESSED 0

Uncompressed point format.

Definition at line 354 of file ecp.h.

## ◆ MBEDTLS_ECP_TLS_NAMED_CURVE

#define MBEDTLS_ECP_TLS_NAMED_CURVE 3

The named_curve of ECCurveType.

Definition at line 360 of file ecp.h.

## ◆ MBEDTLS_ECP_WINDOW_SIZE

#define MBEDTLS_ECP_WINDOW_SIZE 6

The maximum window size used.

Definition at line 247 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_ALLOC_FAILED

#define MBEDTLS_ERR_ECP_ALLOC_FAILED -0x4D80

Memory allocation failed.

Definition at line 55 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_BAD_INPUT_DATA

#define MBEDTLS_ERR_ECP_BAD_INPUT_DATA -0x4F80

Bad input parameters to function.

Definition at line 51 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL

#define MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL -0x4F00

The buffer is too small to write to.

Definition at line 52 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE

#define MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE -0x4E80

The requested feature is not available, for example, the requested curve is not supported.

Definition at line 53 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_HW_ACCEL_FAILED

#define MBEDTLS_ERR_ECP_HW_ACCEL_FAILED -0x4B80

The ECP hardware accelerator failed.

Definition at line 61 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_IN_PROGRESS

#define MBEDTLS_ERR_ECP_IN_PROGRESS -0x4B00

Operation in progress, call again with the same parameters to continue.

Definition at line 63 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_INVALID_KEY

#define MBEDTLS_ERR_ECP_INVALID_KEY -0x4C80

Invalid private or public key.

Definition at line 57 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_RANDOM_FAILED

#define MBEDTLS_ERR_ECP_RANDOM_FAILED -0x4D00

Generation of random value, such as ephemeral key, failed.

Definition at line 56 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH

#define MBEDTLS_ERR_ECP_SIG_LEN_MISMATCH -0x4C00

The buffer contains a valid signature followed by more data.

Definition at line 58 of file ecp.h.

## ◆ MBEDTLS_ERR_ECP_VERIFY_FAILED

#define MBEDTLS_ERR_ECP_VERIFY_FAILED -0x4E00

The signature is not valid.

Definition at line 54 of file ecp.h.

## Typedef Documentation

## ◆ mbedtls_ecp_curve_info

typedef struct mbedtls_ecp_curve_info mbedtls_ecp_curve_info

Curve information, for use by other modules.

## ◆ mbedtls_ecp_group

typedef struct mbedtls_ecp_group mbedtls_ecp_group

The ECP group structure.

We consider two types of curve equations:

- Short Weierstrass: `y^2 = x^3 + A x + B mod P` (SEC1 + RFC-4492)
- Montgomery: `y^2 = x^3 + A x^2 + x mod P` (Curve25519, Curve448)

In both cases, the generator (`G`) for a prime-order subgroup is fixed.

For Short Weierstrass, this subgroup is the whole curve, and its cardinality is denoted by `N`. Our code requires that `N` is an odd prime as mbedtls_ecp_mul() requires an odd number, and mbedtls_ecdsa_sign() requires that it is prime for blinding purposes.

For Montgomery curves, we do not store `A`, but `(A + 2) / 4`, which is the quantity used in the formulas. Additionally, `nbits` is not the size of `N` but the required size for private keys.

If `modp` is NULL, reduction modulo `P` is done using a generic algorithm. Otherwise, `modp` must point to a function that takes an `mbedtls_mpi` in the range of `0..2^(2*pbits)-1`, and transforms it in-place to an integer which is congruent mod `P` to the given MPI, and is close enough to `pbits` in size, so that it may be efficiently brought in the 0..P-1 range by a few additions or subtractions. Therefore, it is only an approximative modular reduction. It must return 0 on success and non-zero on failure.

Note
  Alternative implementations must keep the group IDs distinct. If two group structures have the same ID, then they must be identical.

## ◆ mbedtls_ecp_keypair

typedef struct mbedtls_ecp_keypair mbedtls_ecp_keypair

The ECP key-pair structure.

A generic key-pair that may be used for ECDSA and fixed ECDH, for example.

Note
  Members are deliberately in the same order as in the mbedtls_ecdsa_context structure.

## ◆ mbedtls_ecp_point

typedef struct mbedtls_ecp_point mbedtls_ecp_point

The ECP point structure, in Jacobian coordinates.

Note
  All functions expect and return points satisfying the following condition: `Z == 0` or `Z == 1`. Other values of `Z` are used only by internal functions. The point is zero, or "at infinity", if `Z == 0`. Otherwise, `X` and `Y` are its standard (affine) coordinates.

## ◆ mbedtls_ecp_restart_ctx

typedef void mbedtls_ecp_restart_ctx

Definition at line 330 of file ecp.h.

## Enumeration Type Documentation

## ◆ mbedtls_ecp_curve_type

enum mbedtls_ecp_curve_type

Enumerator
MBEDTLS_ECP_TYPE_NONE |
MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS |
MBEDTLS_ECP_TYPE_MONTGOMERY |

Definition at line 105 of file ecp.h.

## ◆ mbedtls_ecp_group_id

enum mbedtls_ecp_group_id

Domain-parameter identifiers: curve, subgroup, and generator.

Note
  Only curves over prime fields are supported.

Warning
  This library does not support validation of arbitrary domain parameters. Therefore, only standardized domain parameters from trusted sources should be used. See mbedtls_ecp_group_load().

Enumerator
MBEDTLS_ECP_DP_NONE | Curve not defined.
MBEDTLS_ECP_DP_SECP192R1 | Domain parameters for the 192-bit curve defined by FIPS 186-4 and SEC1.
MBEDTLS_ECP_DP_SECP224R1 | Domain parameters for the 224-bit curve defined by FIPS 186-4 and SEC1.
MBEDTLS_ECP_DP_SECP256R1 | Domain parameters for the 256-bit curve defined by FIPS 186-4 and SEC1.
MBEDTLS_ECP_DP_SECP384R1 | Domain parameters for the 384-bit curve defined by FIPS 186-4 and SEC1.
MBEDTLS_ECP_DP_SECP521R1 | Domain parameters for the 521-bit curve defined by FIPS 186-4 and SEC1.
MBEDTLS_ECP_DP_BP256R1 | Domain parameters for 256-bit Brainpool curve.
MBEDTLS_ECP_DP_BP384R1 | Domain parameters for 384-bit Brainpool curve.
MBEDTLS_ECP_DP_BP512R1 | Domain parameters for 512-bit Brainpool curve.
MBEDTLS_ECP_DP_CURVE25519 | Domain parameters for Curve25519.
MBEDTLS_ECP_DP_SECP192K1 | Domain parameters for 192-bit "Koblitz" curve.
MBEDTLS_ECP_DP_SECP224K1 | Domain parameters for 224-bit "Koblitz" curve.
MBEDTLS_ECP_DP_SECP256K1 | Domain parameters for 256-bit "Koblitz" curve.
MBEDTLS_ECP_DP_CURVE448 | Domain parameters for Curve448.

Definition at line 77 of file ecp.h.

## Function Documentation

## ◆ mbedtls_ecp_check_privkey()

int mbedtls_ecp_check_privkey | ( | const mbedtls_ecp_group * | grp,
|  | const mbedtls_mpi * | d
| ) |  |

This function checks that an `mbedtls_mpi` is a valid private key for this curve.

Note
  This function uses bare components rather than an mbedtls_ecp_keypair structure to ease use with other structures, such as mbedtls_ecdh_context or mbedtls_ecdsa_context.

Parameters

  grp | The ECP group the private key should belong to. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  d | The integer to check. This must be initialized.

Returns
  `0` if the point is a valid private key.
  MBEDTLS_ERR_ECP_INVALID_KEY if the point is not a valid private key for the given curve.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_check_pub_priv()

int mbedtls_ecp_check_pub_priv | ( | const mbedtls_ecp_keypair * | pub,
|  | const mbedtls_ecp_keypair * | prv
| ) |  |

This function checks that the keypair objects `pub` and `prv` have the same group and the same public point, and that the private key in `prv` is consistent with the public key.

Parameters

  pub | The keypair structure holding the public key. This must be initialized. If it contains a private key, that part is ignored.
  prv | The keypair structure holding the full keypair. This must be initialized.

Returns
  `0` on success, meaning that the keys are valid and match.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if the keys are invalid or do not match.
  An `MBEDTLS_ERR_ECP_XXX` or an `MBEDTLS_ERR_MPI_XXX` error code on calculation failure.

## ◆ mbedtls_ecp_check_pubkey()

int mbedtls_ecp_check_pubkey | ( | const mbedtls_ecp_group * | grp,
|  | const mbedtls_ecp_point * | pt
| ) |  |

This function checks that a point is a valid public key on this curve.

It only checks that the point is non-zero, has valid coordinates and lies on the curve. It does not verify that it is indeed a multiple of `G`. This additional check is computationally more expensive, is not required by standards, and should not be necessary if the group used has a small cofactor. In particular, it is useless for the NIST groups which all have a cofactor of 1.

Note
  This function uses bare components rather than an mbedtls_ecp_keypair structure, to ease use with other structures, such as mbedtls_ecdh_context or mbedtls_ecdsa_context.

Parameters

  grp | The ECP group the point should belong to. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  pt | The point to check. This must be initialized.

Returns
  `0` if the point is a valid public key.
  MBEDTLS_ERR_ECP_INVALID_KEY if the point is not a valid public key for the given curve.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_copy()

int mbedtls_ecp_copy | ( | mbedtls_ecp_point * | P,
|  | const mbedtls_ecp_point * | Q
| ) |  |

This function copies the contents of point `Q` into point `P`.

Parameters

  P | The destination point. This must be initialized.
  Q | The source point. This must be initialized.

Returns
  `0` on success.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  Another negative error code for other kinds of failure.

## ◆ mbedtls_ecp_curve_info_from_grp_id()

const mbedtls_ecp_curve_info* mbedtls_ecp_curve_info_from_grp_id | ( | mbedtls_ecp_group_id | grp_id | ) |

This function retrieves curve information from an internal group identifier.

Parameters

  grp_id | An `MBEDTLS_ECP_DP_XXX` value.

Returns
  The associated curve information on success.
  NULL on failure.

## ◆ mbedtls_ecp_curve_info_from_name()

const mbedtls_ecp_curve_info* mbedtls_ecp_curve_info_from_name | ( | const char * | name | ) |

This function retrieves curve information from a human-readable name.

Parameters

  name | The human-readable name.

Returns
  The associated curve information on success.
  NULL on failure.

## ◆ mbedtls_ecp_curve_info_from_tls_id()

const mbedtls_ecp_curve_info* mbedtls_ecp_curve_info_from_tls_id | ( | uint16_t | tls_id | ) |

This function retrieves curve information from a TLS NamedCurve value.

Parameters

  tls_id | An `MBEDTLS_ECP_DP_XXX` value.

Returns
  The associated curve information on success.
  NULL on failure.

## ◆ mbedtls_ecp_curve_list()

const mbedtls_ecp_curve_info* mbedtls_ecp_curve_list | ( | void |  | ) |

This function retrieves the information defined in mbedtls_ecp_curve_info() for all supported curves in order of preference.

Note
  This function returns information about all curves supported by the library. Some curves may not be supported for all algorithms. Call mbedtls_ecdh_can_do() or mbedtls_ecdsa_can_do() to check if a curve is supported for ECDH or ECDSA.

Returns
  A statically allocated array. The last entry is 0.

## ◆ mbedtls_ecp_gen_key()

int mbedtls_ecp_gen_key | ( | mbedtls_ecp_group_id | grp_id,
|  | mbedtls_ecp_keypair * | key,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function generates an ECP key.

Parameters

  grp_id | The ECP group identifier.
  key | The destination 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` doesn't need a context argument.

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

## ◆ mbedtls_ecp_gen_keypair()

int mbedtls_ecp_gen_keypair | ( | 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 ECP keypair.

Note
  This function uses bare components rather than an mbedtls_ecp_keypair structure to ease use with other structures, such as mbedtls_ecdh_context or mbedtls_ecdsa_context.

Parameters

  grp | The ECP group to generate a key pair for. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  d | The destination MPI (secret part). This must be initialized.
  Q | The destination point (public part). This must be initialized.
  f_rng | The RNG function. This must not be `NULL`.
  p_rng | The RNG context to be passed to `f_rng`. This may be `NULL` if `f_rng` doesn't need a context argument.

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

## ◆ mbedtls_ecp_gen_keypair_base()

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

This function generates a keypair with a configurable base point.

Note
  This function uses bare components rather than an mbedtls_ecp_keypair structure to ease use with other structures, such as mbedtls_ecdh_context or mbedtls_ecdsa_context.

Parameters

  grp | The ECP group to generate a key pair for. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  G | The base point to use. This must be initialized and belong to `grp`. It replaces the default base point `grp->G` used by mbedtls_ecp_gen_keypair().
  d | The destination MPI (secret part). This must be initialized.
  Q | The destination point (public part). This must be initialized.
  f_rng | The RNG function. This must not be `NULL`.
  p_rng | The RNG context to be passed to `f_rng`. This may be `NULL` if `f_rng` doesn't need a context argument.

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

## ◆ mbedtls_ecp_gen_privkey()

int mbedtls_ecp_gen_privkey | ( | const mbedtls_ecp_group * | grp,
|  | mbedtls_mpi * | d,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function generates a private key.

Parameters

  grp | The ECP group to generate a private key for. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  d | The destination MPI (secret part). This must be initialized.
  f_rng | The RNG function. This must not be `NULL`.
  p_rng | The RNG parameter to be passed to `f_rng`. This may be `NULL` if `f_rng` doesn't need a context argument.

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

## ◆ mbedtls_ecp_get_type()

mbedtls_ecp_curve_type mbedtls_ecp_get_type | ( | const mbedtls_ecp_group * | grp | ) |

## ◆ mbedtls_ecp_group_copy()

int mbedtls_ecp_group_copy | ( | mbedtls_ecp_group * | dst,
|  | const mbedtls_ecp_group * | src
| ) |  |

This function copies the contents of group `src` into group `dst`.

Parameters

  dst | The destination group. This must be initialized.
  src | The source group. This must be initialized.

Returns
  `0` on success.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_group_free()

void mbedtls_ecp_group_free | ( | mbedtls_ecp_group * | grp | ) |

This function frees the components of an ECP group.

Parameters

  grp | The group to free. This may be `NULL`, in which case this function returns immediately. If it is not `NULL`, it must point to an initialized ECP group.

## ◆ mbedtls_ecp_group_init()

void mbedtls_ecp_group_init | ( | mbedtls_ecp_group * | grp | ) |

This function initializes an ECP group context without loading any domain parameters.

Note
  After this function is called, domain parameters for various ECP groups can be loaded through the mbedtls_ecp_group_load() or mbedtls_ecp_tls_read_group() functions.

## ◆ mbedtls_ecp_group_load()

int mbedtls_ecp_group_load | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_group_id | id
| ) |  |

This function sets up an ECP group context from a standardized set of domain parameters.

Note
  The index should be a value of the NamedCurve enum, as defined in RFC-4492: Elliptic Curve Cryptography (ECC) Cipher Suites for Transport Layer Security (TLS), usually in the form of an `MBEDTLS_ECP_DP_XXX` macro.

Parameters

  grp | The group context to setup. This must be initialized.
  id | The identifier of the domain parameter set to load.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if `id` doesn't correspond to a known group.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_grp_id_list()

const mbedtls_ecp_group_id* mbedtls_ecp_grp_id_list | ( | void |  | ) |

This function retrieves the list of internal group identifiers of all supported curves in the order of preference.

Note
  This function returns information about all curves supported by the library. Some curves may not be supported for all algorithms. Call mbedtls_ecdh_can_do() or mbedtls_ecdsa_can_do() to check if a curve is supported for ECDH or ECDSA.

Returns
  A statically allocated array, terminated with MBEDTLS_ECP_DP_NONE.

## ◆ mbedtls_ecp_is_zero()

int mbedtls_ecp_is_zero | ( | mbedtls_ecp_point * | pt | ) |

This function checks if a point is the point at infinity.

Parameters

  pt | The point to test. This must be initialized.

Returns
  `1` if the point is zero.
  `0` if the point is non-zero.
  A negative error code on failure.

## ◆ mbedtls_ecp_keypair_free()

void mbedtls_ecp_keypair_free | ( | mbedtls_ecp_keypair * | key | ) |

This function frees the components of a key pair.

Parameters

  key | The key pair to free. This may be `NULL`, in which case this function returns immediately. If it is not `NULL`, it must point to an initialized ECP key pair.

## ◆ mbedtls_ecp_keypair_init()

void mbedtls_ecp_keypair_init | ( | mbedtls_ecp_keypair * | key | ) |

This function initializes a key pair as an invalid one.

Parameters

  key | The key pair to initialize.

## ◆ mbedtls_ecp_mul()

int mbedtls_ecp_mul | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_point * | R,
|  | const mbedtls_mpi * | m,
|  | const mbedtls_ecp_point * | P,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng
| ) |  |

This function performs a scalar multiplication of a point by an integer: `R` = `m` * `P`.

It is not thread-safe to use same group in multiple threads.

Note
  To prevent timing attacks, this function executes the exact same sequence of base-field operations for any valid `m`. It avoids any if-branch or array index depending on the value of `m`.
  If `f_rng` is not NULL, it is used to randomize intermediate results to prevent potential timing attacks targeting these results. We recommend always providing a non-NULL `f_rng`. The overhead is negligible. Note: unless #MBEDTLS_ECP_NO_INTERNAL_RNG is defined, when `f_rng` is NULL, an internal RNG (seeded from the value of `m`) will be used instead.

Parameters

  grp | The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  R | The point in which to store the result of the calculation. This must be initialized.
  m | The integer by which to multiply. This must be initialized.
  P | The point to multiply. This must be initialized.
  f_rng | The RNG function. This may be `NULL` if randomization of intermediate results isn't desired (discouraged).
  p_rng | The RNG context to be passed to `p_rng`.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_INVALID_KEY if `m` is not a valid private key, or `P` is not a valid public key.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_mul_restartable()

int mbedtls_ecp_mul_restartable | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_point * | R,
|  | const mbedtls_mpi * | m,
|  | const mbedtls_ecp_point * | P,
|  | int(*)(void *, unsigned char *, size_t) | f_rng,
|  | void * | p_rng,
|  | mbedtls_ecp_restart_ctx * | rs_ctx
| ) |  |

This function performs multiplication of a point by an integer: `R` = `m` * `P` in a restartable way.

See also
  mbedtls_ecp_mul()

Note
  This function does the same as `mbedtls_ecp_mul()`, but it can return early and restart according to the limit set with `mbedtls_ecp_set_max_ops()` to reduce blocking.

Parameters

  grp | The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  R | The point in which to store the result of the calculation. This must be initialized.
  m | The integer by which to multiply. This must be initialized.
  P | The point to multiply. This must be initialized.
  f_rng | The RNG function. This may be `NULL` if randomization of intermediate results isn't desired (discouraged).
  p_rng | The RNG context to be passed to `p_rng`.
  rs_ctx | The restart context (NULL disables restart).

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_INVALID_KEY if `m` is not a valid private key, or `P` is not a valid public key.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see `mbedtls_ecp_set_max_ops()`.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_muladd()

int mbedtls_ecp_muladd | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_point * | R,
|  | const mbedtls_mpi * | m,
|  | const mbedtls_ecp_point * | P,
|  | const mbedtls_mpi * | n,
|  | const mbedtls_ecp_point * | Q
| ) |  |

This function performs multiplication and addition of two points by integers: `R` = `m` * `P` + `n` * `Q`.

It is not thread-safe to use same group in multiple threads.

Note
  In contrast to mbedtls_ecp_mul(), this function does not guarantee a constant execution flow and timing.

Parameters

  grp | The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  R | The point in which to store the result of the calculation. This must be initialized.
  m | The integer by which to multiply `P`. This must be initialized.
  P | The point to multiply by `m`. This must be initialized.
  n | The integer by which to multiply `Q`. This must be initialized.
  Q | The point to be multiplied by `n`. This must be initialized.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_INVALID_KEY if `m` or `n` are not valid private keys, or `P` or `Q` are not valid public keys.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_muladd_restartable()

int mbedtls_ecp_muladd_restartable | ( | mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_point * | R,
|  | const mbedtls_mpi * | m,
|  | const mbedtls_ecp_point * | P,
|  | const mbedtls_mpi * | n,
|  | const mbedtls_ecp_point * | Q,
|  | mbedtls_ecp_restart_ctx * | rs_ctx
| ) |  |

This function performs multiplication and addition of two points by integers: `R` = `m` * `P` + `n` * `Q` in a restartable way.

See also
  `mbedtls_ecp_muladd()`

Note
  This function works the same as `mbedtls_ecp_muladd()`, but it can return early and restart according to the limit set with `mbedtls_ecp_set_max_ops()` to reduce blocking.

Parameters

  grp | The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  R | The point in which to store the result of the calculation. This must be initialized.
  m | The integer by which to multiply `P`. This must be initialized.
  P | The point to multiply by `m`. This must be initialized.
  n | The integer by which to multiply `Q`. This must be initialized.
  Q | The point to be multiplied by `n`. This must be initialized.
  rs_ctx | The restart context (NULL disables restart).

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_INVALID_KEY if `m` or `n` are not valid private keys, or `P` or `Q` are not valid public keys.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of operations was reached: see `mbedtls_ecp_set_max_ops()`.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_point_cmp()

int mbedtls_ecp_point_cmp | ( | const mbedtls_ecp_point * | P,
|  | const mbedtls_ecp_point * | Q
| ) |  |

This function compares two points.

Note
  This assumes that the points are normalized. Otherwise, they may compare as "not equal" even if they are.

Parameters

  P | The first point to compare. This must be initialized.
  Q | The second point to compare. This must be initialized.

Returns
  `0` if the points are equal.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if the points are not equal.

## ◆ mbedtls_ecp_point_free()

void mbedtls_ecp_point_free | ( | mbedtls_ecp_point * | pt | ) |

This function frees the components of a point.

Parameters

  pt | The point to free.

## ◆ mbedtls_ecp_point_init()

void mbedtls_ecp_point_init | ( | mbedtls_ecp_point * | pt | ) |

This function initializes a point as zero.

Parameters

  pt | The point to initialize.

## ◆ mbedtls_ecp_point_read_binary()

int mbedtls_ecp_point_read_binary | ( | const mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_point * | P,
|  | const unsigned char * | buf,
|  | size_t | ilen
| ) |  |

This function imports a point from unsigned binary data.

Note
  This function does not check that the point actually belongs to the given group, see mbedtls_ecp_check_pubkey() for that.

Parameters

  grp | The group to which the point should belong. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  P | The destination context to import the point to. This must be initialized.
  buf | The input buffer. This must be a readable buffer of length `ilen` Bytes.
  ilen | The length of the input buffer `buf` in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if the input is invalid.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the import for the given group is not implemented.

## ◆ mbedtls_ecp_point_read_string()

int mbedtls_ecp_point_read_string | ( | mbedtls_ecp_point * | P,
|  | int | radix,
|  | const char * | x,
|  | const char * | y
| ) |  |

This function imports a non-zero point from two ASCII strings.

Parameters

  P | The destination point. This must be initialized.
  radix | The numeric base of the input.
  x | The first affine coordinate, as a null-terminated string.
  y | The second affine coordinate, as a null-terminated string.

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

## ◆ mbedtls_ecp_point_write_binary()

int mbedtls_ecp_point_write_binary | ( | const mbedtls_ecp_group * | grp,
|  | const mbedtls_ecp_point * | P,
|  | int | format,
|  | size_t * | olen,
|  | unsigned char * | buf,
|  | size_t | buflen
| ) |  |

This function exports a point into unsigned binary data.

Parameters

  grp | The group to which the point should belong. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  P | The point to export. This must be initialized.
  format | The point format. This must be either MBEDTLS_ECP_PF_COMPRESSED or MBEDTLS_ECP_PF_UNCOMPRESSED. (For groups without these formats, this parameter is ignored. But it still has to be either of the above values.)
  olen | The address at which to store the length of the output in Bytes. This must not be `NULL`.
  buf | The output buffer. This must be a writable buffer of length `buflen` Bytes.
  buflen | The length of the output buffer `buf` in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the output buffer is too small to hold the point.
  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the point format or the export for the given group is not implemented.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_read_key()

int mbedtls_ecp_read_key | ( | mbedtls_ecp_group_id | grp_id,
|  | mbedtls_ecp_keypair * | key,
|  | const unsigned char * | buf,
|  | size_t | buflen
| ) |  |

This function reads an elliptic curve private key.

Parameters

  grp_id | The ECP group identifier.
  key | The destination key.
  buf | The the buffer containing the binary representation of the key. (Big endian integer for Weierstrass curves, byte string for Montgomery curves.)
  buflen | The length of the buffer in bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_INVALID_KEY error if the key is invalid.
  MBEDTLS_ERR_MPI_ALLOC_FAILED if memory allocation failed.
  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the operation for the group is not implemented.
  Another negative error code on different kinds of failure.

## ◆ mbedtls_ecp_self_test()

int mbedtls_ecp_self_test | ( | int | verbose | ) |

The ECP checkup routine.

Returns
  `0` on success.
  `1` on failure.

## ◆ mbedtls_ecp_set_zero()

int mbedtls_ecp_set_zero | ( | mbedtls_ecp_point * | pt | ) |

This function sets a point to the point at infinity.

Parameters

  pt | The point to set. This must be initialized.

Returns
  `0` on success.
  MBEDTLS_ERR_MPI_ALLOC_FAILED on memory-allocation failure.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_tls_read_group()

int mbedtls_ecp_tls_read_group | ( | mbedtls_ecp_group * | grp,
|  | const unsigned char ** | buf,
|  | size_t | len
| ) |  |

This function sets up an ECP group context from a TLS ECParameters record as defined in RFC 4492, Section 5.4.

Note
  The read pointer `buf` is updated to point right after the ECParameters record on exit.

Parameters

  grp | The group context to setup. This must be initialized.
  buf | The address of the pointer to the start of the input buffer.
  len | The length of the input buffer `*buf` in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid.
  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the group is not recognized.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_tls_read_group_id()

int mbedtls_ecp_tls_read_group_id | ( | mbedtls_ecp_group_id * | grp,
|  | const unsigned char ** | buf,
|  | size_t | len
| ) |  |

This function extracts an elliptic curve group ID from a TLS ECParameters record as defined in RFC 4492, Section 5.4.

Note
  The read pointer `buf` is updated to point right after the ECParameters record on exit.

Parameters

  grp | The address at which to store the group id. This must not be `NULL`.
  buf | The address of the pointer to the start of the input buffer.
  len | The length of the input buffer `*buf` in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid.
  MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE if the group is not recognized.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_tls_read_point()

int mbedtls_ecp_tls_read_point | ( | const mbedtls_ecp_group * | grp,
|  | mbedtls_ecp_point * | pt,
|  | const unsigned char ** | buf,
|  | size_t | len
| ) |  |

This function imports a point from a TLS ECPoint record.

Note
  On function return, `*buf` is updated to point immediately after the ECPoint record.

Parameters

  grp | The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  pt | The destination point.
  buf | The address of the pointer to the start of the input buffer.
  len | The length of the buffer.

Returns
  `0` on success.
  An `MBEDTLS_ERR_MPI_XXX` error code on initialization failure.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if input is invalid.

## ◆ mbedtls_ecp_tls_write_group()

int mbedtls_ecp_tls_write_group | ( | const mbedtls_ecp_group * | grp,
|  | size_t * | olen,
|  | unsigned char * | buf,
|  | size_t | blen
| ) |  |

This function exports an elliptic curve as a TLS ECParameters record as defined in RFC 4492, Section 5.4.

Parameters

  grp | The ECP group to be exported. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  olen | The address at which to store the number of Bytes written. This must not be `NULL`.
  buf | The buffer to write to. This must be a writable buffer of length `blen` Bytes.
  blen | The length of the output buffer `buf` in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the output buffer is too small to hold the exported group.
  Another negative error code on other kinds of failure.

## ◆ mbedtls_ecp_tls_write_point()

int mbedtls_ecp_tls_write_point | ( | const mbedtls_ecp_group * | grp,
|  | const mbedtls_ecp_point * | pt,
|  | int | format,
|  | size_t * | olen,
|  | unsigned char * | buf,
|  | size_t | blen
| ) |  |

This function exports a point as a TLS ECPoint record defined in RFC 4492, Section 5.4.

Parameters

  grp | The ECP group to use. This must be initialized and have group parameters set, for example through mbedtls_ecp_group_load().
  pt | The point to be exported. This must be initialized.
  format | The point format to use. This must be either MBEDTLS_ECP_PF_COMPRESSED or MBEDTLS_ECP_PF_UNCOMPRESSED.
  olen | The address at which to store the length in Bytes of the data written.
  buf | The target buffer. This must be a writable buffer of length `blen` Bytes.
  blen | The length of the target buffer `buf` in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_ECP_BAD_INPUT_DATA if the input is invalid.
  MBEDTLS_ERR_ECP_BUFFER_TOO_SMALL if the target buffer is too small to hold the exported point.
  Another negative error code on other kinds of failure.