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Improve ECDH documentation

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- Rephrase file/function/parameter/enum/define/error descriptions into full
  and clear sentences.
- Make sure to adhere to the Arm writing guidelines.
- Fix missing/incorrect Doxygen tags.
- Standardize terminology used within the file.

GitHub PR: #1317
This commit is contained in:
Rose Zadik 2018-01-25 21:57:43 +00:00 committed by Jaeden Amero
parent 042e97fa75
commit de2d6221c8
1 changed files with 150 additions and 88 deletions
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238
include/mbedtls/ecdh.h
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@ -1,10 +1,18 @@
/** /**
* \file ecdh.h * \file ecdh.h
* *
* \brief Elliptic curve Diffie-Hellman * \brief The Elliptic Curve Diffie-Hellman (ECDH) protocol APIs.
*
* ECDH 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 <em>NIST SP 800-56A Rev. 2: Recommendation for
* Pair-Wise Key Establishment Schemes Using Discrete Logarithm
* Cryptography</em>.
*/ */
/* /*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved * Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved
* SPDX-License-Identifier: Apache-2.0 * SPDX-License-Identifier: Apache-2.0
* *
* Licensed under the Apache License, Version 2.0 (the "License"); you may * Licensed under the Apache License, Version 2.0 (the "License"); you may
@ -19,8 +27,9 @@
* See the License for the specific language governing permissions and * See the License for the specific language governing permissions and
* limitations under the License. * limitations under the License.
* *
* This file is part of mbed TLS (https://tls.mbed.org) * This file is part of Mbed TLS (https://tls.mbed.org)
*/ */
#ifndef MBEDTLS_ECDH_H #ifndef MBEDTLS_ECDH_H
#define MBEDTLS_ECDH_H #define MBEDTLS_ECDH_H
@ -31,7 +40,9 @@ extern "C" {
#endif #endif
/** /**
* When importing from an EC key, select if it is our key or the peer's key * Defines the source of the imported EC key:
* <ul><li>Our key.</li>
* <li>The key of the peer.</li></ul>
*/ */
typedef enum typedef enum
{ {
@ -40,56 +51,67 @@ typedef enum
} mbedtls_ecdh_side; } mbedtls_ecdh_side;
/** /**
* \brief ECDH context structure * \brief The ECDH context structure.
*/ */
typedef struct typedef struct
{ {
mbedtls_ecp_group grp; /*!< elliptic curve used */ mbedtls_ecp_group grp; /*!< The elliptic curve used. */
mbedtls_mpi d; /*!< our secret value (private key) */ mbedtls_mpi d; /*!< The private key. */
mbedtls_ecp_point Q; /*!< our public value (public key) */ mbedtls_ecp_point Q; /*!< The public key. */
mbedtls_ecp_point Qp; /*!< peer's public value (public key) */ mbedtls_ecp_point Qp; /*!< The value of the public key of the peer. */
mbedtls_mpi z; /*!< shared secret */ mbedtls_mpi z; /*!< The shared secret. */
int point_format; /*!< format for point export in TLS messages */ int point_format; /*!< The format of point export in TLS messages. */
mbedtls_ecp_point Vi; /*!< blinding value (for later) */ mbedtls_ecp_point Vi; /*!< The blinding value. */
mbedtls_ecp_point Vf; /*!< un-blinding value (for later) */ mbedtls_ecp_point Vf; /*!< The unblinding value. */
mbedtls_mpi _d; /*!< previous d (for later) */ mbedtls_mpi _d; /*!< The previous \p d. */
} }
mbedtls_ecdh_context; mbedtls_ecdh_context;
/** /**
* \brief Generate a public key. * \brief This function generates an ECDH keypair on an elliptic
* Raw function that only does the core computation. * curve.
* *
* \param grp ECP group * This function performs the first of two core computations
* \param d Destination MPI (secret exponent, aka private key) * implemented during the ECDH key exchange. The second core
* \param Q Destination point (public key) * computation is performed by mbedtls_ecdh_compute_shared().
* \param f_rng RNG function
* \param p_rng RNG parameter
* *
* \return 0 if successful, * \param grp The ECP group.
* or a MBEDTLS_ERR_ECP_XXX or MBEDTLS_MPI_XXX error code * \param d The destination MPI (private key).
* \param Q The destination point (public key).
* \param f_rng The RNG function.
* \param p_rng The RNG parameter.
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX or
* \c MBEDTLS_MPI_XXX error code on failure.
*
* \see ecp.h
*/ */
int mbedtls_ecdh_gen_public( mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q, int mbedtls_ecdh_gen_public( mbedtls_ecp_group *grp, mbedtls_mpi *d, mbedtls_ecp_point *Q,
int (*f_rng)(void *, unsigned char *, size_t), int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng ); void *p_rng );
/** /**
* \brief Compute shared secret * \brief This function computes the shared secret.
* Raw function that only does the core computation.
* *
* \param grp ECP group * This function performs the second of two core computations
* \param z Destination MPI (shared secret) * implemented during the ECDH key exchange. The first core
* \param Q Public key from other party * computation is performed by mbedtls_ecdh_gen_public().
* \param d Our secret exponent (private key)
* \param f_rng RNG function (see notes)
* \param p_rng RNG parameter
* *
* \return 0 if successful, * \param grp The ECP group.
* or a MBEDTLS_ERR_ECP_XXX or MBEDTLS_MPI_XXX error code * \param z The destination MPI (shared secret).
* \param Q The public key from another party.
* \param d Our secret exponent (private key).
* \param f_rng The RNG function.
* \param p_rng The RNG parameter.
* *
* \note If f_rng is not NULL, it is used to implement * \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX or
* \c MBEDTLS_MPI_XXX error code on failure.
*
* \see ecp.h
*
* \note If \p f_rng is not NULL, it is used to implement
* countermeasures against potential elaborate timing * countermeasures against potential elaborate timing
* attacks, see \c mbedtls_ecp_mul() for details. * attacks. For more information, see mbedtls_ecp_mul().
*/ */
int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z, int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
const mbedtls_ecp_point *Q, const mbedtls_mpi *d, const mbedtls_ecp_point *Q, const mbedtls_mpi *d,
@ -97,34 +119,41 @@ int mbedtls_ecdh_compute_shared( mbedtls_ecp_group *grp, mbedtls_mpi *z,
void *p_rng ); void *p_rng );
/** /**
* \brief Initialize context * \brief This function initializes an ECDH context.
* *
* \param ctx Context to initialize * \param ctx The ECDH context to initialize.
*/ */
void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx ); void mbedtls_ecdh_init( mbedtls_ecdh_context *ctx );
/** /**
* \brief Free context * \brief This function frees a context.
* *
* \param ctx Context to free * \param ctx The context to free.
*/ */
void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx ); void mbedtls_ecdh_free( mbedtls_ecdh_context *ctx );
/** /**
* \brief Generate a public key and a TLS ServerKeyExchange payload. * \brief This function generates a public key and a TLS
* (First function used by a TLS server for ECDHE.) * ServerKeyExchange payload.
* *
* \param ctx ECDH context * This is the first function used by a TLS server for ECDHE
* \param olen number of chars written * ciphersuites.
* \param buf destination buffer
* \param blen length of buffer
* \param f_rng RNG function
* \param p_rng RNG parameter
* *
* \note This function assumes that ctx->grp has already been * \param ctx The ECDH context.
* properly set (for example using mbedtls_ecp_group_load). * \param olen The number of characters written.
* \param buf The destination buffer.
* \param blen The length of the destination buffer.
* \param f_rng The RNG function.
* \param p_rng The RNG parameter.
* *
* \return 0 if successful, or an MBEDTLS_ERR_ECP_XXX error code * \note This function assumes that the ECP group (grp) of the
* \p ctx context has already been properly set,
* for example, using mbedtls_ecp_group_load().
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX error code
* on failure.
*
* \see ecp.h
*/ */
int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen, int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
unsigned char *buf, size_t blen, unsigned char *buf, size_t blen,
@ -132,45 +161,63 @@ int mbedtls_ecdh_make_params( mbedtls_ecdh_context *ctx, size_t *olen,
void *p_rng ); void *p_rng );
/** /**
* \brief Parse and procress a TLS ServerKeyExhange payload. * \brief This function parses and processes a TLS ServerKeyExhange
* (First function used by a TLS client for ECDHE.) * payload.
* *
* \param ctx ECDH context * This is the first function used by a TLS client for ECDHE
* \param buf pointer to start of input buffer * ciphersuites.
* \param end one past end of buffer
* *
* \return 0 if successful, or an MBEDTLS_ERR_ECP_XXX error code * \param ctx The ECDH context.
* \param buf The pointer to the start of the input buffer.
* \param end The address for one Byte past the end of the buffer.
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX error code
* on failure.
*
* \see ecp.h
*/ */
int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx, int mbedtls_ecdh_read_params( mbedtls_ecdh_context *ctx,
const unsigned char **buf, const unsigned char *end ); const unsigned char **buf, const unsigned char *end );
/** /**
* \brief Setup an ECDH context from an EC key. * \brief This function sets up an ECDH context from an EC key.
* (Used by clients and servers in place of the
* ServerKeyEchange for static ECDH: import ECDH parameters
* from a certificate's EC key information.)
* *
* \param ctx ECDH constext to set * It is used by clients and servers in place of the
* \param key EC key to use * ServerKeyEchange for static ECDH, and imports ECDH
* \param side Is it our key (1) or the peer's key (0) ? * parameters from the EC key information of a certificate.
* *
* \return 0 if successful, or an MBEDTLS_ERR_ECP_XXX error code * \param ctx The ECDH context to set up.
* \param key The EC key to use.
* \param side Defines the source of the key:
* <ul><li>1: Our key.</li>
<li>0: The key of the peer.</li></ul>
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX error code
* on failure.
*
* \see ecp.h
*/ */
int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key, int mbedtls_ecdh_get_params( mbedtls_ecdh_context *ctx, const mbedtls_ecp_keypair *key,
mbedtls_ecdh_side side ); mbedtls_ecdh_side side );
/** /**
* \brief Generate a public key and a TLS ClientKeyExchange payload. * \brief This function generates a public key and a TLS
* (Second function used by a TLS client for ECDH(E).) * ClientKeyExchange payload.
* *
* \param ctx ECDH context * This is the second function used by a TLS client for ECDH(E)
* \param olen number of bytes actually written * ciphersuites.
* \param buf destination buffer
* \param blen size of destination buffer
* \param f_rng RNG function
* \param p_rng RNG parameter
* *
* \return 0 if successful, or an MBEDTLS_ERR_ECP_XXX error code * \param ctx The ECDH context.
* \param olen The number of Bytes written.
* \param buf The destination buffer.
* \param blen The size of the destination buffer.
* \param f_rng The RNG function.
* \param p_rng The RNG parameter.
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX error code
* on failure.
*
* \see ecp.h
*/ */
int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen, int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
unsigned char *buf, size_t blen, unsigned char *buf, size_t blen,
@ -178,30 +225,45 @@ int mbedtls_ecdh_make_public( mbedtls_ecdh_context *ctx, size_t *olen,
void *p_rng ); void *p_rng );
/** /**
* \brief Parse and process a TLS ClientKeyExchange payload. * \brief This function parses and processes a TLS ClientKeyExchange
* (Second function used by a TLS server for ECDH(E).) * payload.
* *
* \param ctx ECDH context * This is the second function used by a TLS server for ECDH(E)
* \param buf start of input buffer * ciphersuites.
* \param blen length of input buffer
* *
* \return 0 if successful, or an MBEDTLS_ERR_ECP_XXX error code * \param ctx The ECDH context.
* \param buf The start of the input buffer.
* \param blen The length of the input buffer.
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX error code
* on failure.
*
* \see ecp.h
*/ */
int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx, int mbedtls_ecdh_read_public( mbedtls_ecdh_context *ctx,
const unsigned char *buf, size_t blen ); const unsigned char *buf, size_t blen );
/** /**
* \brief Derive and export the shared secret. * \brief This function derives and exports the shared secret.
* (Last function used by both TLS client en servers.)
* *
* \param ctx ECDH context * This is the last function used by both TLS client
* \param olen number of bytes written * and servers.
* \param buf destination buffer
* \param blen buffer length
* \param f_rng RNG function, see notes for \c mbedtls_ecdh_compute_shared()
* \param p_rng RNG parameter
* *
* \return 0 if successful, or an MBEDTLS_ERR_ECP_XXX error code * \param ctx The ECDH context.
* \param olen The number of Bytes written.
* \param buf The destination buffer.
* \param blen The length of the destination buffer.
* \param f_rng The RNG function.
* \param p_rng The RNG parameter.
*
* \return \c 0 on success, or an \c MBEDTLS_ERR_ECP_XXX error code
* on failure.
*
* \see ecp.h
*
* \note If \p f_rng is not NULL, it is used to implement
* countermeasures against potential elaborate timing
* attacks. For more information, see mbedtls_ecp_mul().
*/ */
int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen, int mbedtls_ecdh_calc_secret( mbedtls_ecdh_context *ctx, size_t *olen,
unsigned char *buf, size_t blen, unsigned char *buf, size_t blen,