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 /**
  * \file pk.h
  *
  * \brief Public Key abstraction layer
  */
 /*
  *  Copyright The Mbed TLS Contributors
  *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
  */
 
 #ifndef MBEDTLS_PK_H
 #define MBEDTLS_PK_H
 #include "mbedtls/private_access.h"
 
 #include "mbedtls/build_info.h"
 
 #include "mbedtls/md.h"
 
 #if defined(MBEDTLS_RSA_C)
 #include "mbedtls/rsa.h"
 #endif
 
 #if defined(MBEDTLS_ECP_C)
 #include "mbedtls/ecp.h"
 #endif
 
 #if defined(MBEDTLS_ECDSA_C)
 #include "mbedtls/ecdsa.h"
 #endif
 
 #if defined(MBEDTLS_PSA_CRYPTO_CLIENT)
 #include "psa/crypto.h"
 #endif
 
 /** Memory allocation failed. */
 #define MBEDTLS_ERR_PK_ALLOC_FAILED        -0x3F80
 /** Type mismatch, eg attempt to encrypt with an ECDSA key */
 #define MBEDTLS_ERR_PK_TYPE_MISMATCH       -0x3F00
 /** Bad input parameters to function. */
 #define MBEDTLS_ERR_PK_BAD_INPUT_DATA      -0x3E80
 /** Read/write of file failed. */
 #define MBEDTLS_ERR_PK_FILE_IO_ERROR       -0x3E00
 /** Unsupported key version */
 #define MBEDTLS_ERR_PK_KEY_INVALID_VERSION -0x3D80
 /** Invalid key tag or value. */
 #define MBEDTLS_ERR_PK_KEY_INVALID_FORMAT  -0x3D00
 /** Key algorithm is unsupported (only RSA and EC are supported). */
 #define MBEDTLS_ERR_PK_UNKNOWN_PK_ALG      -0x3C80
 /** Private key password can't be empty. */
 #define MBEDTLS_ERR_PK_PASSWORD_REQUIRED   -0x3C00
 /** Given private key password does not allow for correct decryption. */
 #define MBEDTLS_ERR_PK_PASSWORD_MISMATCH   -0x3B80
 /** The pubkey tag or value is invalid (only RSA and EC are supported). */
 #define MBEDTLS_ERR_PK_INVALID_PUBKEY      -0x3B00
 /** The algorithm tag or value is invalid. */
 #define MBEDTLS_ERR_PK_INVALID_ALG         -0x3A80
 /** Elliptic curve is unsupported (only NIST curves are supported). */
 #define MBEDTLS_ERR_PK_UNKNOWN_NAMED_CURVE -0x3A00
 /** Unavailable feature, e.g. RSA disabled for RSA key. */
 #define MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE -0x3980
 /** The buffer contains a valid signature followed by more data. */
 #define MBEDTLS_ERR_PK_SIG_LEN_MISMATCH    -0x3900
 /** The output buffer is too small. */
 #define MBEDTLS_ERR_PK_BUFFER_TOO_SMALL    -0x3880
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /**
  * \brief          Public key types
  */
 typedef enum {
     MBEDTLS_PK_NONE=0,
     MBEDTLS_PK_RSA,
     MBEDTLS_PK_ECKEY,
     MBEDTLS_PK_ECKEY_DH,
     MBEDTLS_PK_ECDSA,
     MBEDTLS_PK_RSA_ALT,
     MBEDTLS_PK_RSASSA_PSS,
     MBEDTLS_PK_OPAQUE,
 } mbedtls_pk_type_t;
 
 /**
  * \brief           Options for RSASSA-PSS signature verification.
  *                  See \c mbedtls_rsa_rsassa_pss_verify_ext()
  */
 typedef struct mbedtls_pk_rsassa_pss_options {
     /** The digest to use for MGF1 in PSS.
      *
      * \note When #MBEDTLS_USE_PSA_CRYPTO is enabled and #MBEDTLS_RSA_C is
      *       disabled, this must be equal to the \c md_alg argument passed
      *       to mbedtls_pk_verify_ext(). In a future version of the library,
      *       this constraint may apply whenever #MBEDTLS_USE_PSA_CRYPTO is
      *       enabled regardless of the status of #MBEDTLS_RSA_C.
      */
     mbedtls_md_type_t mgf1_hash_id;
 
     /** The expected length of the salt, in bytes. This may be
      * #MBEDTLS_RSA_SALT_LEN_ANY to accept any salt length.
      *
      * \note When #MBEDTLS_USE_PSA_CRYPTO is enabled, only
      *       #MBEDTLS_RSA_SALT_LEN_ANY is valid. Any other value may be
      *       ignored (allowing any salt length).
      */
     int expected_salt_len;
 
 } mbedtls_pk_rsassa_pss_options;
 
 /**
  * \brief           Maximum size of a signature made by mbedtls_pk_sign().
  */
 /* We need to set MBEDTLS_PK_SIGNATURE_MAX_SIZE to the maximum signature
  * size among the supported signature types. Do it by starting at 0,
  * then incrementally increasing to be large enough for each supported
  * signature mechanism.
  *
  * The resulting value can be 0, for example if MBEDTLS_ECDH_C is enabled
  * (which allows the pk module to be included) but neither MBEDTLS_ECDSA_C
  * nor MBEDTLS_RSA_C nor any opaque signature mechanism (PSA or RSA_ALT).
  */
 #define MBEDTLS_PK_SIGNATURE_MAX_SIZE 0
 
 #if (defined(MBEDTLS_RSA_C) || defined(MBEDTLS_PK_RSA_ALT_SUPPORT)) && \
     MBEDTLS_MPI_MAX_SIZE > MBEDTLS_PK_SIGNATURE_MAX_SIZE
 /* For RSA, the signature can be as large as the bignum module allows.
  * For RSA_ALT, the signature size is not necessarily tied to what the
  * bignum module can do, but in the absence of any specific setting,
  * we use that (rsa_alt_sign_wrap in library/pk_wrap.h will check). */
 #undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
 #define MBEDTLS_PK_SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
 #endif
 
 #if defined(MBEDTLS_ECDSA_C) &&                                 \
     MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_PK_SIGNATURE_MAX_SIZE
 /* For ECDSA, the ecdsa module exports a constant for the maximum
  * signature size. */
 #undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
 #define MBEDTLS_PK_SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
 #endif
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 #if PSA_SIGNATURE_MAX_SIZE > MBEDTLS_PK_SIGNATURE_MAX_SIZE
 /* PSA_SIGNATURE_MAX_SIZE is the maximum size of a signature made
  * through the PSA API in the PSA representation. */
 #undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
 #define MBEDTLS_PK_SIGNATURE_MAX_SIZE PSA_SIGNATURE_MAX_SIZE
 #endif
 
 #if PSA_VENDOR_ECDSA_SIGNATURE_MAX_SIZE + 11 > MBEDTLS_PK_SIGNATURE_MAX_SIZE
 /* The Mbed TLS representation is different for ECDSA signatures:
  * PSA uses the raw concatenation of r and s,
  * whereas Mbed TLS uses the ASN.1 representation (SEQUENCE of two INTEGERs).
  * Add the overhead of ASN.1: up to (1+2) + 2 * (1+2+1) for the
  * types, lengths (represented by up to 2 bytes), and potential leading
  * zeros of the INTEGERs and the SEQUENCE. */
 #undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
 #define MBEDTLS_PK_SIGNATURE_MAX_SIZE (PSA_VENDOR_ECDSA_SIGNATURE_MAX_SIZE + 11)
 #endif
 #endif /* defined(MBEDTLS_USE_PSA_CRYPTO) */
 
 /* Internal helper to define which fields in the pk_context structure below
  * should be used for EC keys: legacy ecp_keypair or the raw (PSA friendly)
  * format. It should be noted that this only affects how data is stored, not
  * which functions are used for various operations. The overall picture looks
  * like this:
  * - if USE_PSA is not defined and ECP_C is defined then use ecp_keypair data
  *   structure and legacy functions
  * - if USE_PSA is defined and
  *     - if ECP_C then use ecp_keypair structure, convert data to a PSA friendly
  *       format and use PSA functions
  *     - if !ECP_C then use new raw data and PSA functions directly.
  *
  * The main reason for the "intermediate" (USE_PSA + ECP_C) above is that as long
  * as ECP_C is defined mbedtls_pk_ec() gives the user a read/write access to the
  * ecp_keypair structure inside the pk_context so they can modify it using
  * ECP functions which are not under PK module's control.
  */
 #if defined(MBEDTLS_USE_PSA_CRYPTO) && defined(PSA_WANT_KEY_TYPE_ECC_PUBLIC_KEY) && \
     !defined(MBEDTLS_ECP_C)
 #define MBEDTLS_PK_USE_PSA_EC_DATA
 #endif
 
 /**
  * \brief           Types for interfacing with the debug module
  */
 typedef enum {
     MBEDTLS_PK_DEBUG_NONE = 0,
     MBEDTLS_PK_DEBUG_MPI,
     MBEDTLS_PK_DEBUG_ECP,
     MBEDTLS_PK_DEBUG_PSA_EC,
 } mbedtls_pk_debug_type;
 
 /**
  * \brief           Item to send to the debug module
  */
 typedef struct mbedtls_pk_debug_item {
     mbedtls_pk_debug_type MBEDTLS_PRIVATE(type);
     const char *MBEDTLS_PRIVATE(name);
     void *MBEDTLS_PRIVATE(value);
 } mbedtls_pk_debug_item;
 
 /** Maximum number of item send for debugging, plus 1 */
 #define MBEDTLS_PK_DEBUG_MAX_ITEMS 3
 
 /**
  * \brief           Public key information and operations
  *
  * \note        The library does not support custom pk info structures,
  *              only built-in structures returned by
  *              mbedtls_cipher_info_from_type().
  */
 typedef struct mbedtls_pk_info_t mbedtls_pk_info_t;
 
 #define MBEDTLS_PK_MAX_EC_PUBKEY_RAW_LEN \
     PSA_KEY_EXPORT_ECC_PUBLIC_KEY_MAX_SIZE(PSA_VENDOR_ECC_MAX_CURVE_BITS)
 /**
  * \brief           Public key container
  */
 typedef struct mbedtls_pk_context {
     const mbedtls_pk_info_t *MBEDTLS_PRIVATE(pk_info);    /**< Public key information         */
     void *MBEDTLS_PRIVATE(pk_ctx);                        /**< Underlying public key context  */
     /* The following field is used to store the ID of a private key in the
      * following cases:
      * - opaque key when MBEDTLS_USE_PSA_CRYPTO is defined
      * - normal key when MBEDTLS_PK_USE_PSA_EC_DATA is defined. In this case:
      *    - the pk_ctx above is not not used to store the private key anymore.
      *      Actually that field not populated at all in this case because also
      *      the public key will be stored in raw format as explained below
      *    - this ID is used for all private key operations (ex: sign, check
      *      key pair, key write, etc) using PSA functions
      *
      * Note: this private key storing solution only affects EC keys, not the
      *       other ones. The latters still use the pk_ctx to store their own
      *       context. */
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     mbedtls_svc_key_id_t MBEDTLS_PRIVATE(priv_id);      /**< Key ID for opaque keys */
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
     /* The following fields are meant for storing the public key in raw format
      * which is handy for:
      * - easily importing it into the PSA context
      * - reducing the ECP module dependencies in the PK one.
      *
      * When MBEDTLS_PK_USE_PSA_EC_DATA is enabled:
      * - the pk_ctx above is not used anymore for storing the public key
      *   inside the ecp_keypair structure
      * - the following fields are used for all public key operations: signature
      *   verify, key pair check and key write.
      * - For a key pair, priv_id contains the private key. For a public key,
      *   priv_id is null.
      * Of course, when MBEDTLS_PK_USE_PSA_EC_DATA is not enabled, the legacy
      * ecp_keypair structure is used for storing the public key and performing
      * all the operations.
      *
      * Note: This new public key storing solution only works for EC keys, not
      *       other ones. The latters still use pk_ctx to store their own
      *       context.
      */
 #if defined(MBEDTLS_PK_USE_PSA_EC_DATA)
     uint8_t MBEDTLS_PRIVATE(pub_raw)[MBEDTLS_PK_MAX_EC_PUBKEY_RAW_LEN]; /**< Raw public key   */
     size_t MBEDTLS_PRIVATE(pub_raw_len);            /**< Valid bytes in "pub_raw" */
     psa_ecc_family_t MBEDTLS_PRIVATE(ec_family);    /**< EC family of pk */
     size_t MBEDTLS_PRIVATE(ec_bits);                /**< Curve's bits of pk */
 #endif /* MBEDTLS_PK_USE_PSA_EC_DATA */
 } mbedtls_pk_context;
 
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
 /**
  * \brief           Context for resuming operations
  */
 typedef struct {
     const mbedtls_pk_info_t *MBEDTLS_PRIVATE(pk_info);    /**< Public key information         */
     void *MBEDTLS_PRIVATE(rs_ctx);                        /**< Underlying restart context     */
 } mbedtls_pk_restart_ctx;
 #else /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
 /* Now we can declare functions that take a pointer to that */
 typedef void mbedtls_pk_restart_ctx;
 #endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
 
 #if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 /**
  * \brief           Types for RSA-alt abstraction
  */
 typedef int (*mbedtls_pk_rsa_alt_decrypt_func)(void *ctx, size_t *olen,
                                                const unsigned char *input, unsigned char *output,
                                                size_t output_max_len);
 typedef int (*mbedtls_pk_rsa_alt_sign_func)(void *ctx,
                                             int (*f_rng)(void *, unsigned char *, size_t),
                                             void *p_rng,
                                             mbedtls_md_type_t md_alg, unsigned int hashlen,
                                             const unsigned char *hash, unsigned char *sig);
 typedef size_t (*mbedtls_pk_rsa_alt_key_len_func)(void *ctx);
 #endif /* MBEDTLS_PK_RSA_ALT_SUPPORT */
 
 /**
  * \brief           Return information associated with the given PK type
  *
  * \param pk_type   PK type to search for.
  *
  * \return          The PK info associated with the type or NULL if not found.
  */
 const mbedtls_pk_info_t *mbedtls_pk_info_from_type(mbedtls_pk_type_t pk_type);
 
 /**
  * \brief           Initialize a #mbedtls_pk_context (as NONE).
  *
  * \param ctx       The context to initialize.
  *                  This must not be \c NULL.
  */
 void mbedtls_pk_init(mbedtls_pk_context *ctx);
 
 /**
  * \brief           Free the components of a #mbedtls_pk_context.
  *
  * \param ctx       The context to clear. It must have been initialized.
  *                  If this is \c NULL, this function does nothing.
  *
  * \note            For contexts that have been set up with
  *                  mbedtls_pk_setup_opaque(), this does not free the underlying
  *                  PSA key and you still need to call psa_destroy_key()
  *                  independently if you want to destroy that key.
  */
 void mbedtls_pk_free(mbedtls_pk_context *ctx);
 
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
 /**
  * \brief           Initialize a restart context
  *
  * \param ctx       The context to initialize.
  *                  This must not be \c NULL.
  */
 void mbedtls_pk_restart_init(mbedtls_pk_restart_ctx *ctx);
 
 /**
  * \brief           Free the components of a restart context
  *
  * \param ctx       The context to clear. It must have been initialized.
  *                  If this is \c NULL, this function does nothing.
  */
 void mbedtls_pk_restart_free(mbedtls_pk_restart_ctx *ctx);
 #endif /* MBEDTLS_ECDSA_C && MBEDTLS_ECP_RESTARTABLE */
 
 /**
  * \brief           Initialize a PK context with the information given
  *                  and allocates the type-specific PK subcontext.
  *
  * \param ctx       Context to initialize. It must not have been set
  *                  up yet (type #MBEDTLS_PK_NONE).
  * \param info      Information to use
  *
  * \return          0 on success,
  *                  MBEDTLS_ERR_PK_BAD_INPUT_DATA on invalid input,
  *                  MBEDTLS_ERR_PK_ALLOC_FAILED on allocation failure.
  *
  * \note            For contexts holding an RSA-alt key, use
  *                  \c mbedtls_pk_setup_rsa_alt() instead.
  */
 int mbedtls_pk_setup(mbedtls_pk_context *ctx, const mbedtls_pk_info_t *info);
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 /**
  * \brief Initialize a PK context to wrap a PSA key.
  *
  * This function creates a PK context which wraps a PSA key. The PSA wrapped
  * key must be an EC or RSA key pair (DH is not suported in the PK module).
  *
  * Under the hood PSA functions will be used to perform the required
  * operations and, based on the key type, used algorithms will be:
  * * EC:
  *     * verify, verify_ext, sign, sign_ext: ECDSA.
  * * RSA:
  *     * sign, decrypt: use the primary algorithm in the wrapped PSA key;
  *     * sign_ext: RSA PSS if the pk_type is #MBEDTLS_PK_RSASSA_PSS, otherwise
  *       it falls back to the sign() case;
  *     * verify, verify_ext, encrypt: not supported.
  *
  * In order for the above operations to succeed, the policy of the wrapped PSA
  * key must allow the specified algorithm.
  *
  * Opaque PK contexts wrapping an EC keys also support \c mbedtls_pk_check_pair(),
  * whereas RSA ones do not.
  *
  * \warning The PSA wrapped key must remain valid as long as the wrapping PK
  *          context is in use, that is at least between the point this function
  *          is called and the point mbedtls_pk_free() is called on this context.
  *
  * \param ctx The context to initialize. It must be empty (type NONE).
  * \param key The PSA key to wrap, which must hold an ECC or RSA key pair.
  *
  * \return    \c 0 on success.
  * \return    #MBEDTLS_ERR_PK_BAD_INPUT_DATA on invalid input (context already
  *            used, invalid key identifier).
  * \return    #MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE if the key is not an ECC or
  *            RSA key pair.
  * \return    #MBEDTLS_ERR_PK_ALLOC_FAILED on allocation failure.
  */
 int mbedtls_pk_setup_opaque(mbedtls_pk_context *ctx,
                             const mbedtls_svc_key_id_t key);
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 /**
  * \brief           Initialize an RSA-alt context
  *
  * \param ctx       Context to initialize. It must not have been set
  *                  up yet (type #MBEDTLS_PK_NONE).
  * \param key       RSA key pointer
  * \param decrypt_func  Decryption function
  * \param sign_func     Signing function
  * \param key_len_func  Function returning key length in bytes
  *
  * \return          0 on success, or MBEDTLS_ERR_PK_BAD_INPUT_DATA if the
  *                  context wasn't already initialized as RSA_ALT.
  *
  * \note            This function replaces \c mbedtls_pk_setup() for RSA-alt.
  */
 int mbedtls_pk_setup_rsa_alt(mbedtls_pk_context *ctx, void *key,
                              mbedtls_pk_rsa_alt_decrypt_func decrypt_func,
                              mbedtls_pk_rsa_alt_sign_func sign_func,
                              mbedtls_pk_rsa_alt_key_len_func key_len_func);
 #endif /* MBEDTLS_PK_RSA_ALT_SUPPORT */
 
 /**
  * \brief           Get the size in bits of the underlying key
  *
  * \param ctx       The context to query. It must have been initialized.
  *
  * \return          Key size in bits, or 0 on error
  */
 size_t mbedtls_pk_get_bitlen(const mbedtls_pk_context *ctx);
 
 /**
  * \brief           Get the length in bytes of the underlying key
  *
  * \param ctx       The context to query. It must have been initialized.
  *
  * \return          Key length in bytes, or 0 on error
  */
 static inline size_t mbedtls_pk_get_len(const mbedtls_pk_context *ctx)
 {
     return (mbedtls_pk_get_bitlen(ctx) + 7) / 8;
 }
 
 /**
  * \brief           Tell if a context can do the operation given by type
  *
  * \param ctx       The context to query. It must have been initialized.
  * \param type      The desired type.
  *
  * \return          1 if the context can do operations on the given type.
  * \return          0 if the context cannot do the operations on the given
  *                  type. This is always the case for a context that has
  *                  been initialized but not set up, or that has been
  *                  cleared with mbedtls_pk_free().
  */
 int mbedtls_pk_can_do(const mbedtls_pk_context *ctx, mbedtls_pk_type_t type);
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 /**
  * \brief           Tell if context can do the operation given by PSA algorithm
  *
  * \param ctx       The context to query. It must have been initialized.
  * \param alg       PSA algorithm to check against, the following are allowed:
  *                  PSA_ALG_RSA_PKCS1V15_SIGN(hash),
  *                  PSA_ALG_RSA_PSS(hash),
  *                  PSA_ALG_RSA_PKCS1V15_CRYPT,
  *                  PSA_ALG_ECDSA(hash),
  *                  PSA_ALG_ECDH, where hash is a specific hash.
  * \param usage     PSA usage flag to check against, must be composed of:
  *                  PSA_KEY_USAGE_SIGN_HASH
  *                  PSA_KEY_USAGE_DECRYPT
  *                  PSA_KEY_USAGE_DERIVE.
  *                  Context key must match all passed usage flags.
  *
  * \warning         Since the set of allowed algorithms and usage flags may be
  *                  expanded in the future, the return value \c 0 should not
  *                  be taken in account for non-allowed algorithms and usage
  *                  flags.
  *
  * \return          1 if the context can do operations on the given type.
  * \return          0 if the context cannot do the operations on the given
  *                  type, for non-allowed algorithms and usage flags, or
  *                  for a context that has been initialized but not set up
  *                  or that has been cleared with mbedtls_pk_free().
  */
 int mbedtls_pk_can_do_ext(const mbedtls_pk_context *ctx, psa_algorithm_t alg,
                           psa_key_usage_t usage);
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(MBEDTLS_PSA_CRYPTO_CLIENT)
 /**
  * \brief           Determine valid PSA attributes that can be used to
  *                  import a key into PSA.
  *
  * The attributes determined by this function are suitable
  * for calling mbedtls_pk_import_into_psa() to create
  * a PSA key with the same key material.
  *
  * The typical flow of operations involving this function is
  * ```
  * psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
  * int ret = mbedtls_pk_get_psa_attributes(pk, &attributes);
  * if (ret != 0) ...; // error handling omitted
  * // Tweak attributes if desired
  * psa_key_id_t key_id = 0;
  * ret = mbedtls_pk_import_into_psa(pk, &attributes, &key_id);
  * if (ret != 0) ...; // error handling omitted
  * ```
  *
  * \note            This function does not support RSA-alt contexts
  *                  (set up with mbedtls_pk_setup_rsa_alt()).
  *
  * \param[in] pk    The PK context to use. It must have been set up.
  *                  It can either contain a key pair or just a public key.
  * \param usage     A single `PSA_KEY_USAGE_xxx` flag among the following:
  *                  - #PSA_KEY_USAGE_DECRYPT: \p pk must contain a
  *                    key pair. The output \p attributes will contain a
  *                    key pair type, and the usage policy will allow
  *                    #PSA_KEY_USAGE_ENCRYPT as well as
  *                    #PSA_KEY_USAGE_DECRYPT.
  *                  - #PSA_KEY_USAGE_DERIVE: \p pk must contain a
  *                    key pair. The output \p attributes will contain a
  *                    key pair type.
  *                  - #PSA_KEY_USAGE_ENCRYPT: The output
  *                    \p attributes will contain a public key type.
  *                  - #PSA_KEY_USAGE_SIGN_HASH: \p pk must contain a
  *                    key pair. The output \p attributes will contain a
  *                    key pair type, and the usage policy will allow
  *                    #PSA_KEY_USAGE_VERIFY_HASH as well as
  *                    #PSA_KEY_USAGE_SIGN_HASH.
  *                  - #PSA_KEY_USAGE_SIGN_MESSAGE: \p pk must contain a
  *                    key pair. The output \p attributes will contain a
  *                    key pair type, and the usage policy will allow
  *                    #PSA_KEY_USAGE_VERIFY_MESSAGE as well as
  *                    #PSA_KEY_USAGE_SIGN_MESSAGE.
  *                  - #PSA_KEY_USAGE_VERIFY_HASH: The output
  *                    \p attributes will contain a public key type.
  *                  - #PSA_KEY_USAGE_VERIFY_MESSAGE: The output
  *                    \p attributes will contain a public key type.
  * \param[out] attributes
  *                  On success, valid attributes to import the key into PSA.
  *                  - The lifetime and key identifier are unchanged. If the
  *                    attribute structure was initialized or reset before
  *                    calling this function, this will result in a volatile
  *                    key. Call psa_set_key_identifier() before or after this
  *                    function if you wish to create a persistent key. Call
  *                    psa_set_key_lifetime() before or after this function if
  *                    you wish to import the key in a secure element.
  *                  - The key type and bit-size are determined by the contents
  *                    of the PK context. If the PK context contains a key
  *                    pair, the key type can be either a key pair type or
  *                    the corresponding public key type, depending on
  *                    \p usage. If the PK context contains a public key,
  *                    the key type is a public key type.
  *                  - The key's policy is determined by the key type and
  *                    the \p usage parameter. The usage always allows
  *                    \p usage, exporting and copying the key, and
  *                    possibly other permissions as documented for the
  *                    \p usage parameter.
  *                    The permitted algorithm policy is determined as follows
  *                    based on the #mbedtls_pk_type_t type of \p pk,
  *                    the chosen \p usage and other factors:
  *                      - #MBEDTLS_PK_RSA whose underlying
  *                        #mbedtls_rsa_context has the padding mode
  *                        #MBEDTLS_RSA_PKCS_V15:
  *                        #PSA_ALG_RSA_PKCS1V15_SIGN(#PSA_ALG_ANY_HASH)
  *                        if \p usage is SIGN/VERIFY, and
  *                        #PSA_ALG_RSA_PKCS1V15_CRYPT
  *                        if \p usage is ENCRYPT/DECRYPT.
  *                      - #MBEDTLS_PK_RSA whose underlying
  *                        #mbedtls_rsa_context has the padding mode
  *                        #MBEDTLS_RSA_PKCS_V21 and the digest type
  *                        corresponding to the PSA algorithm \c hash:
  *                        #PSA_ALG_RSA_PSS_ANY_SALT(#PSA_ALG_ANY_HASH)
  *                        if \p usage is SIGN/VERIFY, and
  *                        #PSA_ALG_RSA_OAEP(\c hash)
  *                        if \p usage is ENCRYPT/DECRYPT.
  *                      - #MBEDTLS_PK_RSA_ALT: not supported.
  *                      - #MBEDTLS_PK_ECDSA or #MBEDTLS_PK_ECKEY
  *                        if \p usage is SIGN/VERIFY:
  *                        #PSA_ALG_DETERMINISTIC_ECDSA(#PSA_ALG_ANY_HASH)
  *                        if #MBEDTLS_ECDSA_DETERMINISTIC is enabled,
  *                        otherwise #PSA_ALG_ECDSA(#PSA_ALG_ANY_HASH).
  *                      - #MBEDTLS_PK_ECKEY_DH or #MBEDTLS_PK_ECKEY
  *                        if \p usage is DERIVE:
  *                        #PSA_ALG_ECDH.
  *                      - #MBEDTLS_PK_OPAQUE: same as the primary algorithm
  *                        set for the underlying PSA key, except that
  *                        sign/decrypt flags are removed if the type is
  *                        set to a public key type.
  *                        The underlying key must allow \p usage.
  *                        Note that the enrollment algorithm set with
  *                        psa_set_key_enrollment_algorithm() is not copied.
  *
  * \return          0 on success.
  *                  #MBEDTLS_ERR_PK_TYPE_MISMATCH if \p pk does not contain
  *                  a key of the type identified in \p attributes.
  *                  Another error code on other failures.
  */
 int mbedtls_pk_get_psa_attributes(const mbedtls_pk_context *pk,
                                   psa_key_usage_t usage,
                                   psa_key_attributes_t *attributes);
 
 /**
  * \brief           Import a key into the PSA key store.
  *
  * This function is equivalent to calling psa_import_key()
  * with the key material from \p pk.
  *
  * The typical way to use this function is:
  * -# Call mbedtls_pk_get_psa_attributes() to obtain
  *    attributes for the given key.
  * -# If desired, modify the attributes, for example:
  *     - To create a persistent key, call
  *       psa_set_key_identifier() and optionally
  *       psa_set_key_lifetime().
  *     - To import only the public part of a key pair:
  *
  *           psa_set_key_type(&attributes,
  *                            PSA_KEY_TYPE_PUBLIC_KEY_OF_KEY_PAIR(
  *                                psa_get_key_type(&attributes)));
  *     - Restrict the key usage if desired.
  * -# Call mbedtls_pk_import_into_psa().
  *
  * \note            This function does not support RSA-alt contexts
  *                  (set up with mbedtls_pk_setup_rsa_alt()).
  *
  * \param[in] pk    The PK context to use. It must have been set up.
  *                  It can either contain a key pair or just a public key.
  * \param[in] attributes
  *                  The attributes to use for the new key. They must be
  *                  compatible with \p pk. In particular, the key type
  *                  must match the content of \p pk.
  *                  If \p pk contains a key pair, the key type in
  *                  attributes can be either the key pair type or the
  *                  corresponding public key type (to import only the
  *                  public part).
  * \param[out] key_id
  *                  On success, the identifier of the newly created key.
  *                  On error, this is #MBEDTLS_SVC_KEY_ID_INIT.
  *
  * \return          0 on success.
  *                  #MBEDTLS_ERR_PK_TYPE_MISMATCH if \p pk does not contain
  *                  a key of the type identified in \p attributes.
  *                  Another error code on other failures.
  */
 int mbedtls_pk_import_into_psa(const mbedtls_pk_context *pk,
                                const psa_key_attributes_t *attributes,
                                mbedtls_svc_key_id_t *key_id);
 
 /**
  * \brief           Create a PK context starting from a key stored in PSA.
  *                  This key:
  *                  - must be exportable and
  *                  - must be an RSA or EC key pair or public key (FFDH is not supported in PK).
  *
  *                  The resulting PK object will be a transparent type:
  *                  - #MBEDTLS_PK_RSA for RSA keys or
  *                  - #MBEDTLS_PK_ECKEY for EC keys.
  *
  *                  Once this functions returns the PK object will be completely
  *                  independent from the original PSA key that it was generated
  *                  from.
  *                  Calling mbedtls_pk_sign(), mbedtls_pk_verify(),
  *                  mbedtls_pk_encrypt(), mbedtls_pk_decrypt() on the resulting
  *                  PK context will perform the corresponding algorithm for that
  *                  PK context type.
  *                  * For ECDSA, the choice of deterministic vs randomized will
  *                    be based on the compile-time setting #MBEDTLS_ECDSA_DETERMINISTIC.
  *                  * For an RSA key, the output PK context will allow both
  *                    encrypt/decrypt and sign/verify regardless of the original
  *                    key's policy.
  *                    The original key's policy determines the output key's padding
  *                    mode: PCKS1 v2.1 is set if the PSA key policy is OAEP or PSS,
  *                    otherwise PKCS1 v1.5 is set.
  *
  * \param key_id    The key identifier of the key stored in PSA.
  * \param pk        The PK context that will be filled. It must be initialized,
  *                  but not set up.
  *
  * \return          0 on success.
  * \return          #MBEDTLS_ERR_PK_BAD_INPUT_DATA in case the provided input
  *                  parameters are not correct.
  */
 int mbedtls_pk_copy_from_psa(mbedtls_svc_key_id_t key_id, mbedtls_pk_context *pk);
 
 /**
  * \brief           Create a PK context for the public key of a PSA key.
  *
  *                  The key must be an RSA or ECC key. It can be either a
  *                  public key or a key pair, and only the public key is copied.
  *                  The resulting PK object will be a transparent type:
  *                  - #MBEDTLS_PK_RSA for RSA keys or
  *                  - #MBEDTLS_PK_ECKEY for EC keys.
  *
  *                  Once this functions returns the PK object will be completely
  *                  independent from the original PSA key that it was generated
  *                  from.
  *                  Calling mbedtls_pk_verify() or
  *                  mbedtls_pk_encrypt() on the resulting
  *                  PK context will perform the corresponding algorithm for that
  *                  PK context type.
  *
  *                  For an RSA key, the output PK context will allow both
  *                  encrypt and verify regardless of the original key's policy.
  *                  The original key's policy determines the output key's padding
  *                  mode: PCKS1 v2.1 is set if the PSA key policy is OAEP or PSS,
  *                  otherwise PKCS1 v1.5 is set.
  *
  * \param key_id    The key identifier of the key stored in PSA.
  * \param pk        The PK context that will be filled. It must be initialized,
  *                  but not set up.
  *
  * \return          0 on success.
  * \return          MBEDTLS_ERR_PK_BAD_INPUT_DATA in case the provided input
  *                  parameters are not correct.
  */
 int mbedtls_pk_copy_public_from_psa(mbedtls_svc_key_id_t key_id, mbedtls_pk_context *pk);
 #endif /* MBEDTLS_PSA_CRYPTO_CLIENT */
 
 /**
  * \brief           Verify signature (including padding if relevant).
  *
  * \param ctx       The PK context to use. It must have been set up.
  * \param md_alg    Hash algorithm used.
  *                  This can be #MBEDTLS_MD_NONE if the signature algorithm
  *                  does not rely on a hash algorithm (non-deterministic
  *                  ECDSA, RSA PKCS#1 v1.5).
  *                  For PKCS#1 v1.5, if \p md_alg is #MBEDTLS_MD_NONE, then
  *                  \p hash is the DigestInfo structure used by RFC 8017
  *                  &sect;9.2 steps 3&ndash;6. If \p md_alg is a valid hash
  *                  algorithm then \p hash is the digest itself, and this
  *                  function calculates the DigestInfo encoding internally.
  * \param hash      Hash of the message to sign
  * \param hash_len  Hash length
  * \param sig       Signature to verify
  * \param sig_len   Signature length
  *
  * \note            For keys of type #MBEDTLS_PK_RSA, the signature algorithm is
  *                  either PKCS#1 v1.5 or PSS (accepting any salt length),
  *                  depending on the padding mode in the underlying RSA context.
  *                  For a pk object constructed by parsing, this is PKCS#1 v1.5
  *                  by default. Use mbedtls_pk_verify_ext() to explicitly select
  *                  a different algorithm.
  *
  * \return          0 on success (signature is valid),
  *                  #MBEDTLS_ERR_PK_SIG_LEN_MISMATCH if there is a valid
  *                  signature in \p sig but its length is less than \p sig_len,
  *                  or a specific error code.
  */
 int mbedtls_pk_verify(mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                       const unsigned char *hash, size_t hash_len,
                       const unsigned char *sig, size_t sig_len);
 
 /**
  * \brief           Restartable version of \c mbedtls_pk_verify()
  *
  * \note            Performs the same job as \c mbedtls_pk_verify(), but can
  *                  return early and restart according to the limit set with
  *                  \c mbedtls_ecp_set_max_ops() to reduce blocking for ECC
  *                  operations. For RSA, same as \c mbedtls_pk_verify().
  *
  * \param ctx       The PK context to use. It must have been set up.
  * \param md_alg    Hash algorithm used (see notes)
  * \param hash      Hash of the message to sign
  * \param hash_len  Hash length or 0 (see notes)
  * \param sig       Signature to verify
  * \param sig_len   Signature length
  * \param rs_ctx    Restart context (NULL to disable restart)
  *
  * \return          See \c mbedtls_pk_verify(), or
  * \return          #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
  *                  operations was reached: see \c mbedtls_ecp_set_max_ops().
  */
 int mbedtls_pk_verify_restartable(mbedtls_pk_context *ctx,
                                   mbedtls_md_type_t md_alg,
                                   const unsigned char *hash, size_t hash_len,
                                   const unsigned char *sig, size_t sig_len,
                                   mbedtls_pk_restart_ctx *rs_ctx);
 
 /**
  * \brief           Verify signature, with options.
  *                  (Includes verification of the padding depending on type.)
  *
  * \param type      Signature type (inc. possible padding type) to verify
  * \param options   Pointer to type-specific options, or NULL
  * \param ctx       The PK context to use. It must have been set up.
  * \param md_alg    Hash algorithm used (see notes)
  * \param hash      Hash of the message to sign
  * \param hash_len  Hash length or 0 (see notes)
  * \param sig       Signature to verify
  * \param sig_len   Signature length
  *
  * \return          0 on success (signature is valid),
  *                  #MBEDTLS_ERR_PK_TYPE_MISMATCH if the PK context can't be
  *                  used for this type of signatures,
  *                  #MBEDTLS_ERR_PK_SIG_LEN_MISMATCH if there is a valid
  *                  signature in \p sig but its length is less than \p sig_len,
  *                  or a specific error code.
  *
  * \note            If hash_len is 0, then the length associated with md_alg
  *                  is used instead, or an error returned if it is invalid.
  *
  * \note            md_alg may be MBEDTLS_MD_NONE, only if hash_len != 0
  *
  * \note            If type is MBEDTLS_PK_RSASSA_PSS, then options must point
  *                  to a mbedtls_pk_rsassa_pss_options structure,
  *                  otherwise it must be NULL. Note that if
  *                  #MBEDTLS_USE_PSA_CRYPTO is defined, the salt length is not
  *                  verified as PSA_ALG_RSA_PSS_ANY_SALT is used.
  */
 int mbedtls_pk_verify_ext(mbedtls_pk_type_t type, const void *options,
                           mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                           const unsigned char *hash, size_t hash_len,
                           const unsigned char *sig, size_t sig_len);
 
 /**
  * \brief           Make signature, including padding if relevant.
  *
  * \param ctx       The PK context to use. It must have been set up
  *                  with a private key.
  * \param md_alg    Hash algorithm used (see notes)
  * \param hash      Hash of the message to sign
  * \param hash_len  Hash length
  * \param sig       Place to write the signature.
  *                  It must have enough room for the signature.
  *                  #MBEDTLS_PK_SIGNATURE_MAX_SIZE is always enough.
  *                  You may use a smaller buffer if it is large enough
  *                  given the key type.
  * \param sig_size  The size of the \p sig buffer in bytes.
  * \param sig_len   On successful return,
  *                  the number of bytes written to \p sig.
  * \param f_rng     RNG function, must not be \c NULL.
  * \param p_rng     RNG parameter
  *
  * \note            For keys of type #MBEDTLS_PK_RSA, the signature algorithm is
  *                  either PKCS#1 v1.5 or PSS (using the largest possible salt
  *                  length up to the hash length), depending on the padding mode
  *                  in the underlying RSA context. For a pk object constructed
  *                  by parsing, this is PKCS#1 v1.5 by default. Use
  *                  mbedtls_pk_verify_ext() to explicitly select a different
  *                  algorithm.
  *
  * \return          0 on success, or a specific error code.
  *
  * \note            For RSA, md_alg may be MBEDTLS_MD_NONE if hash_len != 0.
  *                  For ECDSA, md_alg may never be MBEDTLS_MD_NONE.
  */
 int mbedtls_pk_sign(mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
                     const unsigned char *hash, size_t hash_len,
                     unsigned char *sig, size_t sig_size, size_t *sig_len,
                     int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);
 
 /**
  * \brief           Make signature given a signature type.
  *
  * \param pk_type   Signature type.
  * \param ctx       The PK context to use. It must have been set up
  *                  with a private key.
  * \param md_alg    Hash algorithm used (see notes)
  * \param hash      Hash of the message to sign
  * \param hash_len  Hash length
  * \param sig       Place to write the signature.
  *                  It must have enough room for the signature.
  *                  #MBEDTLS_PK_SIGNATURE_MAX_SIZE is always enough.
  *                  You may use a smaller buffer if it is large enough
  *                  given the key type.
  * \param sig_size  The size of the \p sig buffer in bytes.
  * \param sig_len   On successful return,
  *                  the number of bytes written to \p sig.
  * \param f_rng     RNG function, must not be \c NULL.
  * \param p_rng     RNG parameter
  *
  * \return          0 on success, or a specific error code.
  *
  * \note            When \p pk_type is #MBEDTLS_PK_RSASSA_PSS,
  *                  see #PSA_ALG_RSA_PSS for a description of PSS options used.
  *
  * \note            For RSA, md_alg may be MBEDTLS_MD_NONE if hash_len != 0.
  *                  For ECDSA, md_alg may never be MBEDTLS_MD_NONE.
  *
  */
 int mbedtls_pk_sign_ext(mbedtls_pk_type_t pk_type,
                         mbedtls_pk_context *ctx,
                         mbedtls_md_type_t md_alg,
                         const unsigned char *hash, size_t hash_len,
                         unsigned char *sig, size_t sig_size, size_t *sig_len,
                         int (*f_rng)(void *, unsigned char *, size_t),
                         void *p_rng);
 
 /**
  * \brief           Restartable version of \c mbedtls_pk_sign()
  *
  * \note            Performs the same job as \c mbedtls_pk_sign(), but can
  *                  return early and restart according to the limit set with
  *                  \c mbedtls_ecp_set_max_ops() to reduce blocking for ECC
  *                  operations. For RSA, same as \c mbedtls_pk_sign().
  *
  * \param ctx       The PK context to use. It must have been set up
  *                  with a private key.
  * \param md_alg    Hash algorithm used (see notes for mbedtls_pk_sign())
  * \param hash      Hash of the message to sign
  * \param hash_len  Hash length
  * \param sig       Place to write the signature.
  *                  It must have enough room for the signature.
  *                  #MBEDTLS_PK_SIGNATURE_MAX_SIZE is always enough.
  *                  You may use a smaller buffer if it is large enough
  *                  given the key type.
  * \param sig_size  The size of the \p sig buffer in bytes.
  * \param sig_len   On successful return,
  *                  the number of bytes written to \p sig.
  * \param f_rng     RNG function, must not be \c NULL.
  * \param p_rng     RNG parameter
  * \param rs_ctx    Restart context (NULL to disable restart)
  *
  * \return          See \c mbedtls_pk_sign().
  * \return          #MBEDTLS_ERR_ECP_IN_PROGRESS if maximum number of
  *                  operations was reached: see \c mbedtls_ecp_set_max_ops().
  */
 int mbedtls_pk_sign_restartable(mbedtls_pk_context *ctx,
                                 mbedtls_md_type_t md_alg,
                                 const unsigned char *hash, size_t hash_len,
                                 unsigned char *sig, size_t sig_size, size_t *sig_len,
                                 int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
                                 mbedtls_pk_restart_ctx *rs_ctx);
 
 /**
  * \brief           Decrypt message (including padding if relevant).
  *
  * \param ctx       The PK context to use. It must have been set up
  *                  with a private key.
  * \param input     Input to decrypt
  * \param ilen      Input size
  * \param output    Decrypted output
  * \param olen      Decrypted message length
  * \param osize     Size of the output buffer
  * \param f_rng     RNG function, must not be \c NULL.
  * \param p_rng     RNG parameter
  *
  * \note            For keys of type #MBEDTLS_PK_RSA, the signature algorithm is
  *                  either PKCS#1 v1.5 or OAEP, depending on the padding mode in
  *                  the underlying RSA context. For a pk object constructed by
  *                  parsing, this is PKCS#1 v1.5 by default.
  *
  * \return          0 on success, or a specific error code.
  */
 int mbedtls_pk_decrypt(mbedtls_pk_context *ctx,
                        const unsigned char *input, size_t ilen,
                        unsigned char *output, size_t *olen, size_t osize,
                        int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);
 
 /**
  * \brief           Encrypt message (including padding if relevant).
  *
  * \param ctx       The PK context to use. It must have been set up.
  * \param input     Message to encrypt
  * \param ilen      Message size
  * \param output    Encrypted output
  * \param olen      Encrypted output length
  * \param osize     Size of the output buffer
  * \param f_rng     RNG function, must not be \c NULL.
  * \param p_rng     RNG parameter
  *
  * \note            For keys of type #MBEDTLS_PK_RSA, the signature algorithm is
  *                  either PKCS#1 v1.5 or OAEP, depending on the padding mode in
  *                  the underlying RSA context. For a pk object constructed by
  *                  parsing, this is PKCS#1 v1.5 by default.
  *
  * \note            \p f_rng is used for padding generation.
  *
  * \return          0 on success, or a specific error code.
  */
 int mbedtls_pk_encrypt(mbedtls_pk_context *ctx,
                        const unsigned char *input, size_t ilen,
                        unsigned char *output, size_t *olen, size_t osize,
                        int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);
 
 /**
  * \brief           Check if a public-private pair of keys matches.
  *
  * \param pub       Context holding a public key.
  * \param prv       Context holding a private (and public) key.
  * \param f_rng     RNG function, must not be \c NULL.
  * \param p_rng     RNG parameter
  *
  * \return          \c 0 on success (keys were checked and match each other).
  * \return          #MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE if the keys could not
  *                  be checked - in that case they may or may not match.
  * \return          #MBEDTLS_ERR_PK_BAD_INPUT_DATA if a context is invalid.
  * \return          Another non-zero value if the keys do not match.
  */
 int mbedtls_pk_check_pair(const mbedtls_pk_context *pub,
                           const mbedtls_pk_context *prv,
                           int (*f_rng)(void *, unsigned char *, size_t),
                           void *p_rng);
 
 /**
  * \brief           Export debug information
  *
  * \param ctx       The PK context to use. It must have been initialized.
  * \param items     Place to write debug items
  *
  * \return          0 on success or MBEDTLS_ERR_PK_BAD_INPUT_DATA
  */
 int mbedtls_pk_debug(const mbedtls_pk_context *ctx, mbedtls_pk_debug_item *items);
 
 /**
  * \brief           Access the type name
  *
  * \param ctx       The PK context to use. It must have been initialized.
  *
  * \return          Type name on success, or "invalid PK"
  */
 const char *mbedtls_pk_get_name(const mbedtls_pk_context *ctx);
 
 /**
  * \brief           Get the key type
  *
  * \param ctx       The PK context to use. It must have been initialized.
  *
  * \return          Type on success.
  * \return          #MBEDTLS_PK_NONE for a context that has not been set up.
  */
 mbedtls_pk_type_t mbedtls_pk_get_type(const mbedtls_pk_context *ctx);
 
 #if defined(MBEDTLS_RSA_C)
 /**
  * Quick access to an RSA context inside a PK context.
  *
  * \warning This function can only be used when the type of the context, as
  * returned by mbedtls_pk_get_type(), is #MBEDTLS_PK_RSA.
  * Ensuring that is the caller's responsibility.
  * Alternatively, you can check whether this function returns NULL.
  *
  * \return The internal RSA context held by the PK context, or NULL.
  */
 static inline mbedtls_rsa_context *mbedtls_pk_rsa(const mbedtls_pk_context pk)
 {
     switch (mbedtls_pk_get_type(&pk)) {
         case MBEDTLS_PK_RSA:
             return (mbedtls_rsa_context *) (pk).MBEDTLS_PRIVATE(pk_ctx);
         default:
             return NULL;
     }
 }
 #endif /* MBEDTLS_RSA_C */
 
 #if defined(MBEDTLS_ECP_C)
 /**
  * Quick access to an EC context inside a PK context.
  *
  * \warning This function can only be used when the type of the context, as
  * returned by mbedtls_pk_get_type(), is #MBEDTLS_PK_ECKEY,
  * #MBEDTLS_PK_ECKEY_DH, or #MBEDTLS_PK_ECDSA.
  * Ensuring that is the caller's responsibility.
  * Alternatively, you can check whether this function returns NULL.
  *
  * \return The internal EC context held by the PK context, or NULL.
  */
 static inline mbedtls_ecp_keypair *mbedtls_pk_ec(const mbedtls_pk_context pk)
 {
     switch (mbedtls_pk_get_type(&pk)) {
         case MBEDTLS_PK_ECKEY:
         case MBEDTLS_PK_ECKEY_DH:
         case MBEDTLS_PK_ECDSA:
             return (mbedtls_ecp_keypair *) (pk).MBEDTLS_PRIVATE(pk_ctx);
         default:
             return NULL;
     }
 }
 #endif /* MBEDTLS_ECP_C */
 
 #if defined(MBEDTLS_PK_PARSE_C)
 /** \ingroup pk_module */
 /**
  * \brief           Parse a private key in PEM or DER format
  *
  * \note            If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
  *                  subsystem must have been initialized by calling
  *                  psa_crypto_init() before calling this function.
  *
  * \param ctx       The PK context to fill. It must have been initialized
  *                  but not set up.
  * \param key       Input buffer to parse.
  *                  The buffer must contain the input exactly, with no
  *                  extra trailing material. For PEM, the buffer must
  *                  contain a null-terminated string.
  * \param keylen    Size of \b key in bytes.
  *                  For PEM data, this includes the terminating null byte,
  *                  so \p keylen must be equal to `strlen(key) + 1`.
  * \param pwd       Optional password for decryption.
  *                  Pass \c NULL if expecting a non-encrypted key.
  *                  Pass a string of \p pwdlen bytes if expecting an encrypted
  *                  key; a non-encrypted key will also be accepted.
  *                  The empty password is not supported.
  * \param pwdlen    Size of the password in bytes.
  *                  Ignored if \p pwd is \c NULL.
  * \param f_rng     RNG function, must not be \c NULL. Used for blinding.
  * \param p_rng     RNG parameter
  *
  * \note            On entry, ctx must be empty, either freshly initialised
  *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
  *                  specific key type, check the result with mbedtls_pk_can_do().
  *
  * \note            The key is also checked for correctness.
  *
  * \return          0 if successful, or a specific PK or PEM error code
  */
 int mbedtls_pk_parse_key(mbedtls_pk_context *ctx,
                          const unsigned char *key, size_t keylen,
                          const unsigned char *pwd, size_t pwdlen,
                          int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);
 
 /** \ingroup pk_module */
 /**
  * \brief           Parse a public key in PEM or DER format
  *
  * \note            If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
  *                  subsystem must have been initialized by calling
  *                  psa_crypto_init() before calling this function.
  *
  * \param ctx       The PK context to fill. It must have been initialized
  *                  but not set up.
  * \param key       Input buffer to parse.
  *                  The buffer must contain the input exactly, with no
  *                  extra trailing material. For PEM, the buffer must
  *                  contain a null-terminated string.
  * \param keylen    Size of \b key in bytes.
  *                  For PEM data, this includes the terminating null byte,
  *                  so \p keylen must be equal to `strlen(key) + 1`.
  *
  * \note            On entry, ctx must be empty, either freshly initialised
  *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
  *                  specific key type, check the result with mbedtls_pk_can_do().
  *
  * \note            For compressed points, see #MBEDTLS_ECP_PF_COMPRESSED for
  *                  limitations.
  *
  * \note            The key is also checked for correctness.
  *
  * \return          0 if successful, or a specific PK or PEM error code
  */
 int mbedtls_pk_parse_public_key(mbedtls_pk_context *ctx,
                                 const unsigned char *key, size_t keylen);
 
 #if defined(MBEDTLS_FS_IO)
 /** \ingroup pk_module */
 /**
  * \brief           Load and parse a private key
  *
  * \note            If #MBEDTLS_USE_PSA_CRYPTO is enabled, the PSA crypto
  *                  subsystem must have been initialized by calling
  *                  psa_crypto_init() before calling this function.
  *
  * \param ctx       The PK context to fill. It must have been initialized
  *                  but not set up.
  * \param path      filename to read the private key from
  * \param password  Optional password to decrypt the file.
  *                  Pass \c NULL if expecting a non-encrypted key.
  *                  Pass a null-terminated string if expecting an encrypted
  *                  key; a non-encrypted key will also be accepted.
  *                  The empty password is not supported.
  * \param f_rng     RNG function, must not be \c NULL. Used for blinding.
  * \param p_rng     RNG parameter
  *
  * \note            On entry, ctx must be empty, either freshly initialised
  *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
  *                  specific key type, check the result with mbedtls_pk_can_do().
  *
  * \note            The key is also checked for correctness.
  *
  * \return          0 if successful, or a specific PK or PEM error code
  */
 int mbedtls_pk_parse_keyfile(mbedtls_pk_context *ctx,
                              const char *path, const char *password,
                              int (*f_rng)(void *, unsigned char *, size_t), void *p_rng);
 
 /** \ingroup pk_module */
 /**
  * \brief           Load and parse a public key
  *
  * \param ctx       The PK context to fill. It must have been initialized
  *                  but not set up.
  * \param path      filename to read the public key from
  *
  * \note            On entry, ctx must be empty, either freshly initialised
  *                  with mbedtls_pk_init() or reset with mbedtls_pk_free(). If
  *                  you need a specific key type, check the result with
  *                  mbedtls_pk_can_do().
  *
  * \note            The key is also checked for correctness.
  *
  * \return          0 if successful, or a specific PK or PEM error code
  */
 int mbedtls_pk_parse_public_keyfile(mbedtls_pk_context *ctx, const char *path);
 #endif /* MBEDTLS_FS_IO */
 #endif /* MBEDTLS_PK_PARSE_C */
 
 #if defined(MBEDTLS_PK_WRITE_C)
 /**
  * \brief           Write a private key to a PKCS#1 or SEC1 DER structure
  *                  Note: data is written at the end of the buffer! Use the
  *                        return value to determine where you should start
  *                        using the buffer
  *
  * \param ctx       PK context which must contain a valid private key.
  * \param buf       buffer to write to
  * \param size      size of the buffer
  *
  * \return          length of data written if successful, or a specific
  *                  error code
  */
 int mbedtls_pk_write_key_der(const mbedtls_pk_context *ctx, unsigned char *buf, size_t size);
 
 /**
  * \brief           Write a public key to a SubjectPublicKeyInfo DER structure
  *                  Note: data is written at the end of the buffer! Use the
  *                        return value to determine where you should start
  *                        using the buffer
  *
  * \param ctx       PK context which must contain a valid public or private key.
  * \param buf       buffer to write to
  * \param size      size of the buffer
  *
  * \return          length of data written if successful, or a specific
  *                  error code
  */
 int mbedtls_pk_write_pubkey_der(const mbedtls_pk_context *ctx, unsigned char *buf, size_t size);
 
 #if defined(MBEDTLS_PEM_WRITE_C)
 /**
  * \brief           Write a public key to a PEM string
  *
  * \param ctx       PK context which must contain a valid public or private key.
  * \param buf       Buffer to write to. The output includes a
  *                  terminating null byte.
  * \param size      Size of the buffer in bytes.
  *
  * \return          0 if successful, or a specific error code
  */
 int mbedtls_pk_write_pubkey_pem(const mbedtls_pk_context *ctx, unsigned char *buf, size_t size);
 
 /**
  * \brief           Write a private key to a PKCS#1 or SEC1 PEM string
  *
  * \param ctx       PK context which must contain a valid private key.
  * \param buf       Buffer to write to. The output includes a
  *                  terminating null byte.
  * \param size      Size of the buffer in bytes.
  *
  * \return          0 if successful, or a specific error code
  */
 int mbedtls_pk_write_key_pem(const mbedtls_pk_context *ctx, unsigned char *buf, size_t size);
 #endif /* MBEDTLS_PEM_WRITE_C */
 #endif /* MBEDTLS_PK_WRITE_C */
 
 /*
  * WARNING: Low-level functions. You probably do not want to use these unless
  *          you are certain you do ;)
  */
 
 #if defined(MBEDTLS_PK_PARSE_C)
 /**
  * \brief           Parse a SubjectPublicKeyInfo DER structure
  *
  * \param p         the position in the ASN.1 data
  * \param end       end of the buffer
  * \param pk        The PK context to fill. It must have been initialized
  *                  but not set up.
  *
  * \return          0 if successful, or a specific PK error code
  */
 int mbedtls_pk_parse_subpubkey(unsigned char **p, const unsigned char *end,
                                mbedtls_pk_context *pk);
 #endif /* MBEDTLS_PK_PARSE_C */
 
 #if defined(MBEDTLS_PK_WRITE_C)
 /**
  * \brief           Write a subjectPublicKey to ASN.1 data
  *                  Note: function works backwards in data buffer
  *
  * \param p         reference to current position pointer
  * \param start     start of the buffer (for bounds-checking)
  * \param key       PK context which must contain a valid public or private key.
  *
  * \return          the length written or a negative error code
  */
 int mbedtls_pk_write_pubkey(unsigned char **p, unsigned char *start,
                             const mbedtls_pk_context *key);
 #endif /* MBEDTLS_PK_WRITE_C */
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif /* MBEDTLS_PK_H */

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