EVP_MD_fetch, EVP_MD_up_ref, EVP_MD_free, EVP_MD_get_params,
  EVP_MD_gettable_params, EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free,
  EVP_MD_CTX_copy, EVP_MD_CTX_copy_ex, EVP_MD_CTX_ctrl, EVP_MD_CTX_set_params,
  EVP_MD_CTX_get_params, EVP_MD_settable_ctx_params, EVP_MD_gettable_ctx_params,
  EVP_MD_CTX_settable_params, EVP_MD_CTX_gettable_params, EVP_MD_CTX_set_flags,
  EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags, EVP_Q_digest, EVP_Digest,
  EVP_DigestInit_ex2, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,
  EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal, EVP_MD_is_a,
  EVP_MD_get0_name, EVP_MD_get0_description, EVP_MD_names_do_all,
  EVP_MD_get0_provider, EVP_MD_get_type, EVP_MD_get_pkey_type, EVP_MD_get_size,
  EVP_MD_get_block_size, EVP_MD_get_flags, EVP_MD_CTX_get0_name, EVP_MD_CTX_md,
  EVP_MD_CTX_get0_md, EVP_MD_CTX_get1_md, EVP_MD_CTX_get_type,
  EVP_MD_CTX_get_size, EVP_MD_CTX_get_block_size, EVP_MD_CTX_get0_md_data,
  EVP_MD_CTX_update_fn, EVP_MD_CTX_set_update_fn, EVP_md_null,
  EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj,
  EVP_MD_CTX_get_pkey_ctx, EVP_MD_CTX_set_pkey_ctx, EVP_MD_do_all_provided,
  EVP_MD_type, EVP_MD_nid, EVP_MD_name, EVP_MD_pkey_type, EVP_MD_size,
  EVP_MD_block_size, EVP_MD_flags, EVP_MD_CTX_size, EVP_MD_CTX_block_size,
  EVP_MD_CTX_type, EVP_MD_CTX_pkey_ctx, EVP_MD_CTX_md_data - EVP digest routines
 #include <openssl/evp.h>
 EVP_MD *EVP_MD_fetch(OSSL_LIB_CTX *ctx, const char *algorithm,
                      const char *properties);
 int EVP_MD_up_ref(EVP_MD *md);
 void EVP_MD_free(EVP_MD *md);
 int EVP_MD_get_params(const EVP_MD *digest, OSSL_PARAM params[]);
 const OSSL_PARAM *EVP_MD_gettable_params(const EVP_MD *digest);
 EVP_MD_CTX *EVP_MD_CTX_new(void);
 int EVP_MD_CTX_reset(EVP_MD_CTX *ctx);
 void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
 void EVP_MD_CTX_ctrl(EVP_MD_CTX *ctx, int cmd, int p1, void* p2);
 int EVP_MD_CTX_get_params(EVP_MD_CTX *ctx, OSSL_PARAM params[]);
 int EVP_MD_CTX_set_params(EVP_MD_CTX *ctx, const OSSL_PARAM params[]);
 const OSSL_PARAM *EVP_MD_settable_ctx_params(const EVP_MD *md);
 const OSSL_PARAM *EVP_MD_gettable_ctx_params(const EVP_MD *md);
 const OSSL_PARAM *EVP_MD_CTX_settable_params(EVP_MD_CTX *ctx);
 const OSSL_PARAM *EVP_MD_CTX_gettable_params(EVP_MD_CTX *ctx);
 void EVP_MD_CTX_set_flags(EVP_MD_CTX *ctx, int flags);
 void EVP_MD_CTX_clear_flags(EVP_MD_CTX *ctx, int flags);
 int EVP_MD_CTX_test_flags(const EVP_MD_CTX *ctx, int flags);
 int EVP_Q_digest(OSSL_LIB_CTX *libctx, const char *name, const char *propq,
                  const void *data, size_t datalen,
                  unsigned char *md, size_t *mdlen);
 int EVP_Digest(const void *data, size_t count, unsigned char *md,
                unsigned int *size, const EVP_MD *type, ENGINE *impl);
 int EVP_DigestInit_ex2(EVP_MD_CTX *ctx, const EVP_MD *type,
                        const OSSL_PARAM params[]);
 int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
 int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
 int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
 int EVP_DigestFinalXOF(EVP_MD_CTX *ctx, unsigned char *md, size_t len);
 int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out, const EVP_MD_CTX *in);
 int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
 int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
 int EVP_MD_CTX_copy(EVP_MD_CTX *out, EVP_MD_CTX *in);
 const char *EVP_MD_get0_name(const EVP_MD *md);
 const char *EVP_MD_get0_description(const EVP_MD *md);
 int EVP_MD_is_a(const EVP_MD *md, const char *name);
 int EVP_MD_names_do_all(const EVP_MD *md,
                         void (*fn)(const char *name, void *data),
                         void *data);
 const OSSL_PROVIDER *EVP_MD_get0_provider(const EVP_MD *md);
 int EVP_MD_get_type(const EVP_MD *md);
 int EVP_MD_get_pkey_type(const EVP_MD *md);
 int EVP_MD_get_size(const EVP_MD *md);
 int EVP_MD_get_block_size(const EVP_MD *md);
 unsigned long EVP_MD_get_flags(const EVP_MD *md);
 const EVP_MD *EVP_MD_CTX_get0_md(const EVP_MD_CTX *ctx);
 EVP_MD *EVP_MD_CTX_get1_md(EVP_MD_CTX *ctx);
 const char *EVP_MD_CTX_get0_name(const EVP_MD_CTX *ctx);
 int EVP_MD_CTX_get_size(const EVP_MD_CTX *ctx);
 int EVP_MD_CTX_get_block_size(const EVP_MD_CTX *ctx);
 int EVP_MD_CTX_get_type(const EVP_MD_CTX *ctx);
 void *EVP_MD_CTX_get0_md_data(const EVP_MD_CTX *ctx);
 const EVP_MD *EVP_md_null(void);
 const EVP_MD *EVP_get_digestbyname(const char *name);
 const EVP_MD *EVP_get_digestbynid(int type);
 const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *o);
 EVP_PKEY_CTX *EVP_MD_CTX_get_pkey_ctx(const EVP_MD_CTX *ctx);
 void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);
 void EVP_MD_do_all_provided(OSSL_LIB_CTX *libctx,
                             void (*fn)(EVP_MD *mac, void *arg),
                             void *arg);
 #define EVP_MD_type EVP_MD_get_type
 #define EVP_MD_nid EVP_MD_get_type
 #define EVP_MD_name EVP_MD_get0_name
 #define EVP_MD_pkey_type EVP_MD_get_pkey_type
 #define EVP_MD_size EVP_MD_get_size
 #define EVP_MD_block_size EVP_MD_get_block_size
 #define EVP_MD_flags EVP_MD_get_flags
 #define EVP_MD_CTX_size EVP_MD_CTX_get_size
 #define EVP_MD_CTX_block_size EVP_MD_CTX_get_block_size
 #define EVP_MD_CTX_type EVP_MD_CTX_get_type
 #define EVP_MD_CTX_pkey_ctx EVP_MD_CTX_get_pkey_ctx
 #define EVP_MD_CTX_md_data EVP_MD_CTX_get0_md_data
The following functions have been deprecated since OpenSSL 3.0,
    and can be hidden entirely by defining OPENSSL_API_COMPAT with a
    suitable version value, see openssl_user_macros(7):
 const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
 int (*EVP_MD_CTX_update_fn(EVP_MD_CTX *ctx))(EVP_MD_CTX *ctx,
                                              const void *data, size_t count);
 void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,
                               int (*update)(EVP_MD_CTX *ctx,
                                             const void *data, size_t count));
The EVP digest routines are a high-level interface to message digests, and
  should be used instead of the digest-specific functions.
The EVP_MD type is a structure for digest method
    implementation.
  - EVP_MD_fetch()
- Fetches the digest implementation for the given algorithm from any
      provider offering it, within the criteria given by the properties.
      See "ALGORITHM FETCHING" in crypto(7) for further
      information.
    The returned value must eventually be freed with
        EVP_MD_free(). Fetched EVP_MD structures are reference counted. 
- EVP_MD_up_ref()
- Increments the reference count for an EVP_MD structure.
- EVP_MD_free()
- Decrements the reference count for the fetched EVP_MD structure. If
      the reference count drops to 0 then the structure is freed.
- EVP_MD_CTX_new()
- Allocates and returns a digest context.
- EVP_MD_CTX_reset()
- Resets the digest context ctx. This can be used to reuse an already
      existing context.
- EVP_MD_CTX_free()
- Cleans up digest context ctx and frees up the space allocated to
      it.
- EVP_MD_CTX_ctrl()
- This is a legacy method. EVP_MD_CTX_set_params()
      and EVP_MD_CTX_get_params() is the mechanism
      that should be used to set and get parameters that are used by
      providers.
    Performs digest-specific control actions on context
        ctx. The control command is indicated in cmd and any
        additional arguments in p1 and p2.
        EVP_MD_CTX_ctrl() must be called after
        EVP_DigestInit_ex2(). Other restrictions may apply depending on
        the control type and digest implementation. If this function happens to be used with a fetched
        EVP_MD, it will translate the controls that are known to OpenSSL
        into OSSL_PARAM(3) parameters with keys defined by OpenSSL and
        call EVP_MD_CTX_get_params() or EVP_MD_CTX_set_params() as
        is appropriate for each control command. See "CONTROLS" below for more information, including
        what translations are being done. 
- EVP_MD_get_params()
- Retrieves the requested list of params from a MD md. See
      "PARAMETERS" below for more information.
- EVP_MD_CTX_get_params()
- Retrieves the requested list of params from a MD context
      ctx. See "PARAMETERS" below for more information.
- EVP_MD_CTX_set_params()
- Sets the list of params into a MD context ctx. See
      "PARAMETERS" below for more information.
- EVP_MD_gettable_params()
- Get a constant OSSL_PARAM(3) array that describes the retrievable
      parameters that can be used with EVP_MD_get_params().
- EVP_MD_gettable_ctx_params(),
    EVP_MD_CTX_gettable_params()
- Get a constant OSSL_PARAM(3) array that describes the retrievable
      parameters that can be used with EVP_MD_CTX_get_params().
      EVP_MD_gettable_ctx_params() returns the parameters that can be
      retrieved from the algorithm, whereas EVP_MD_CTX_gettable_params()
      returns the parameters that can be retrieved in the context's current
      state.
- EVP_MD_settable_ctx_params(),
    EVP_MD_CTX_settable_params()
- Get a constant OSSL_PARAM(3) array that describes the settable
      parameters that can be used with EVP_MD_CTX_set_params().
      EVP_MD_settable_ctx_params() returns the parameters that can be set
      from the algorithm, whereas EVP_MD_CTX_settable_params() returns
      the parameters that can be set in the context's current state.
- EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(),
    EVP_MD_CTX_test_flags()
- Sets, clears and tests ctx flags. See "FLAGS" below for
      more information.
- EVP_Q_digest() is a quick one-shot digest function.
- It hashes datalen bytes of data at data using the digest
      algorithm name, which is fetched using the optional libctx
      and propq parameters. The digest value is placed in md and
      its length is written at mdlen if the pointer is not NULL. At most
      EVP_MAX_MD_SIZE bytes will be written.
- EVP_Digest()
- A wrapper around the Digest Init_ex, Update and Final_ex functions. Hashes
      count bytes of data at data using a digest type from
      ENGINE impl. The digest value is placed in md and its length
      is written at size if the pointer is not NULL. At most
      EVP_MAX_MD_SIZE bytes will be written. If impl is NULL the
      default implementation of digest type is used.
- EVP_DigestInit_ex2()
- Sets up digest context ctx to use a digest type. type
      is typically supplied by a function such as EVP_sha1(), or a value
      explicitly fetched with EVP_MD_fetch().
    The parameters params are set on the context after
        initialisation. The type parameter can be NULL if ctx has been
        already initialized with another EVP_DigestInit_ex() call and has
        not been reset with EVP_MD_CTX_reset(). 
- EVP_DigestInit_ex()
- Sets up digest context ctx to use a digest type. type
      is typically supplied by a function such as EVP_sha1(), or a value
      explicitly fetched with EVP_MD_fetch().
    If impl is non-NULL, its implementation of the digest
        type is used if there is one, and if not, the default
        implementation is used. The type parameter can be NULL if ctx has been
        already initialized with another EVP_DigestInit_ex() call and has
        not been reset with EVP_MD_CTX_reset(). 
- EVP_DigestUpdate()
- Hashes cnt bytes of data at d into the digest context
      ctx. This function can be called several times on the same
      ctx to hash additional data.
- EVP_DigestFinal_ex()
- Retrieves the digest value from ctx and places it in md. If
      the s parameter is not NULL then the number of bytes of data
      written (i.e. the length of the digest) will be written to the integer at
      s, at most EVP_MAX_MD_SIZE bytes will be written. After
      calling EVP_DigestFinal_ex() no additional calls to
      EVP_DigestUpdate() can be made, but EVP_DigestInit_ex2() can
      be called to initialize a new digest operation.
- EVP_DigestFinalXOF()
- Interfaces to extendable-output functions, XOFs, such as SHAKE128 and
      SHAKE256. It retrieves the digest value from ctx and places it in
      len-sized md. After calling this function no additional
      calls to EVP_DigestUpdate() can be made, but
      EVP_DigestInit_ex2() can be called to initialize a new
    operation.
- EVP_MD_CTX_copy_ex()
- Can be used to copy the message digest state from in to out.
      This is useful if large amounts of data are to be hashed which only differ
      in the last few bytes.
- EVP_DigestInit()
- Behaves in the same way as EVP_DigestInit_ex2() except it doesn't
      set any parameters and calls EVP_MD_CTX_reset() so it cannot be
      used with an type of NULL.
- EVP_DigestFinal()
- Similar to EVP_DigestFinal_ex() except after computing the digest
      the digest context ctx is automatically cleaned up with
      EVP_MD_CTX_reset().
- EVP_MD_CTX_copy()
- Similar to EVP_MD_CTX_copy_ex() except the destination out
      does not have to be initialized.
- EVP_MD_is_a()
- Returns 1 if md is an implementation of an algorithm that's
      identifiable with name, otherwise 0.
    If md is a legacy digest (it's the return value from
        the likes of EVP_sha256() rather than the result of an
        EVP_MD_fetch()), only cipher names registered with the default
        library context (see OSSL_LIB_CTX(3)) will be considered. 
- EVP_MD_get0_name(), EVP_MD_CTX_get0_name()
- Return the name of the given message digest. For fetched message digests
      with multiple names, only one of them is returned; it's recommended to use
      EVP_MD_names_do_all() instead.
- EVP_MD_names_do_all()
- Traverses all names for the md, and calls fn with each name
      and data. This is only useful with fetched EVP_MDs.
- EVP_MD_get0_description()
- Returns a description of the digest, meant for display and human
      consumption. The description is at the discretion of the digest
      implementation.
- EVP_MD_get0_provider()
- Returns an OSSL_PROVIDER pointer to the provider that implements
      the given EVP_MD.
- EVP_MD_get_size(), EVP_MD_CTX_get_size()
- Return the size of the message digest when passed an EVP_MD or an
      EVP_MD_CTX structure, i.e. the size of the hash.
- EVP_MD_get_block_size(), EVP_MD_CTX_get_block_size()
- Return the block size of the message digest when passed an EVP_MD
      or an EVP_MD_CTX structure.
- EVP_MD_get_type(), EVP_MD_CTX_get_type()
- Return the NID of the OBJECT IDENTIFIER representing the given message
      digest when passed an EVP_MD structure. For example,
      "EVP_MD_get_type(EVP_sha1())" returns
      NID_sha1. This function is normally used when setting ASN1
    OIDs.
- EVP_MD_CTX_get0_md_data()
- Return the digest method private data for the passed EVP_MD_CTX.
      The space is allocated by OpenSSL and has the size originally set with
      EVP_MD_meth_set_app_datasize().
- EVP_MD_CTX_get0_md(), EVP_MD_CTX_get1_md()
- EVP_MD_CTX_get0_md() returns the EVP_MD structure
      corresponding to the passed EVP_MD_CTX. This will be the same
      EVP_MD object originally passed to EVP_DigestInit_ex2() (or
      other similar function) when the EVP_MD_CTX was first initialised. Note
      that where explicit fetch is in use (see EVP_MD_fetch(3)) the value
      returned from this function will not have its reference count incremented
      and therefore it should not be used after the EVP_MD_CTX is freed.
      EVP_MD_CTX_get1_md() is the same except the ownership is passed to
      the caller and is from the passed EVP_MD_CTX.
- EVP_MD_CTX_set_update_fn()
- Sets the update function for ctx to update. This is the
      function that is called by EVP_DigestUpdate(). If not set, the
      update function from the EVP_MD type specified at initialization is
      used.
- EVP_MD_CTX_update_fn()
- Returns the update function for ctx.
- EVP_MD_get_flags()
- Returns the md flags. Note that these are different from the
      EVP_MD_CTX ones. See EVP_MD_meth_set_flags(3) for more
      information.
- EVP_MD_get_pkey_type()
- Returns the NID of the public key signing algorithm associated with this
      digest. For example EVP_sha1() is associated with RSA so this will
      return NID_sha1WithRSAEncryption. Since digests and signature
      algorithms are no longer linked this function is only retained for
      compatibility reasons.
- EVP_md_null()
- A "null" message digest that does nothing: i.e. the hash it
      returns is of zero length.
- EVP_get_digestbyname(), EVP_get_digestbynid(),
    EVP_get_digestbyobj()
- Returns an EVP_MD structure when passed a digest name, a digest
      NID or an ASN1_OBJECT structure respectively.
    The EVP_get_digestbyname() function is present for
        backwards compatibility with OpenSSL prior to version 3 and is different
        to the EVP_MD_fetch() function since it does not attempt to
        "fetch" an implementation of the cipher. Additionally, it only
        knows about digests that are built-in to OpenSSL and have an associated
        NID. Similarly EVP_get_digestbynid() and
        EVP_get_digestbyobj() also return objects without an associated
        implementation. When the digest objects returned by these functions are used
        (such as in a call to EVP_DigestInit_ex()) an implementation of
        the digest will be implicitly fetched from the loaded providers. This
        fetch could fail if no suitable implementation is available. Use
        EVP_MD_fetch() instead to explicitly fetch the algorithm and an
        associated implementation from a provider. See "ALGORITHM FETCHING" in crypto(7) for
        more information about fetching. The digest objects returned from these functions do not need
        to be freed with EVP_MD_free(). 
- EVP_MD_CTX_get_pkey_ctx()
- Returns the EVP_PKEY_CTX assigned to ctx. The returned
      pointer should not be freed by the caller.
- EVP_MD_CTX_set_pkey_ctx()
- Assigns an EVP_PKEY_CTX to EVP_MD_CTX. This is usually used
      to provide a customized EVP_PKEY_CTX to
      EVP_DigestSignInit(3) or EVP_DigestVerifyInit(3). The
      pctx passed to this function should be freed by the caller. A NULL
      pctx pointer is also allowed to clear the EVP_PKEY_CTX
      assigned to ctx. In such case, freeing the cleared
      EVP_PKEY_CTX or not depends on how the EVP_PKEY_CTX is
      created.
- EVP_MD_do_all_provided()
- Traverses all messages digests implemented by all activated providers in
      the given library context libctx, and for each of the
      implementations, calls the given function fn with the
      implementation method and the given arg as argument.
See OSSL_PARAM(3) for information about passing parameters.EVP_MD_CTX_set_params() can be used with the following
    OSSL_PARAM keys:
  - "xoflen" (OSSL_DIGEST_PARAM_XOFLEN) <unsigned
    integer>
- Sets the digest length for extendable output functions. It is used by the
      SHAKE algorithm and should not exceed what can be given using a
      size_t.
- "pad-type" (OSSL_DIGEST_PARAM_PAD_TYPE) <unsigned
    integer>
- Sets the padding type. It is used by the MDC2 algorithm.
EVP_MD_CTX_get_params() can be used with the following
    OSSL_PARAM keys:
  - "micalg" (OSSL_PARAM_DIGEST_KEY_MICALG) <UTF8
    string>.
- Gets the digest Message Integrity Check algorithm string. This is used
      when creating S/MIME multipart/signed messages, as specified in RFC 3851.
      It may be used by external engines or providers.
EVP_MD_CTX_ctrl() can be used to send the following standard controls:
  - EVP_MD_CTRL_MICALG
- Gets the digest Message Integrity Check algorithm string. This is used
      when creating S/MIME multipart/signed messages, as specified in RFC 3851.
      The string value is written to p2.
    When used with a fetched EVP_MD,
        EVP_MD_CTX_get_params() gets called with an OSSL_PARAM(3)
        item with the key "micalg"
      (OSSL_DIGEST_PARAM_MICALG). 
- EVP_MD_CTRL_XOF_LEN
- This control sets the digest length for extendable output functions to
      p1. Sending this control directly should not be necessary, the use
      of EVP_DigestFinalXOF() is preferred. Currently used by SHAKE.
    When used with a fetched EVP_MD,
        EVP_MD_CTX_get_params() gets called with an OSSL_PARAM(3)
        item with the key "xoflen"
      (OSSL_DIGEST_PARAM_XOFLEN). 
EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags() and
  EVP_MD_CTX_test_flags() can be used the manipulate and test these
  EVP_MD_CTX flags:
  - EVP_MD_CTX_FLAG_ONESHOT
- This flag instructs the digest to optimize for one update only, if
      possible.
- EVP_MD_CTX_FLAG_NO_INIT
- This flag instructs EVP_DigestInit() and similar not to initialise
      the implementation specific data.
- EVP_MD_CTX_FLAG_FINALISE
- Some functions such as EVP_DigestSign only finalise copies of internal
      contexts so additional data can be included after the finalisation call.
      This is inefficient if this functionality is not required, and can be
      disabled with this flag.
  - EVP_MD_fetch()
- Returns a pointer to a EVP_MD for success or NULL for failure.
- EVP_MD_up_ref()
- Returns 1 for success or 0 for failure.
- EVP_Q_digest(), EVP_Digest(), EVP_DigestInit_ex2(),
    EVP_DigestInit_ex(), EVP_DigestInit(),
    EVP_DigestUpdate(), EVP_DigestFinal_ex(),
    EVP_DigestFinalXOF(), and EVP_DigestFinal()
- return 1 for success and 0 for failure.
- EVP_MD_CTX_ctrl()
- Returns 1 if successful or 0 for failure.
- EVP_MD_CTX_set_params(), EVP_MD_CTX_get_params()
- Returns 1 if successful or 0 for failure.
- EVP_MD_CTX_settable_params(),
    EVP_MD_CTX_gettable_params()
- Return an array of constant OSSL_PARAM(3)s, or NULL if there is
      none to get.
- EVP_MD_CTX_copy_ex()
- Returns 1 if successful or 0 for failure.
- EVP_MD_get_type(), EVP_MD_get_pkey_type()
- Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef if
      none exists.
- EVP_MD_get_size(), EVP_MD_get_block_size(),
    EVP_MD_CTX_get_size(), EVP_MD_CTX_get_block_size()
- Returns the digest or block size in bytes or -1 for failure.
- EVP_md_null()
- Returns a pointer to the EVP_MD structure of the "null"
      message digest.
- EVP_get_digestbyname(), EVP_get_digestbynid(),
    EVP_get_digestbyobj()
- Returns either an EVP_MD structure or NULL if an error occurs.
- EVP_MD_CTX_set_pkey_ctx()
- This function has no return value.
- EVP_MD_names_do_all()
- Returns 1 if the callback was called for all names. A return value of 0
      means that the callback was not called for any names.
The EVP interface to message digests should almost always be used in
  preference to the low-level interfaces. This is because the code then becomes
  transparent to the digest used and much more flexible.New applications should use the SHA-2 (such as
    EVP_sha256(3)) or the SHA-3 digest algorithms (such as
    EVP_sha3_512(3)). The other digest algorithms are still in common
    use.
For most applications the impl parameter to
    EVP_DigestInit_ex() will be set to NULL to use the default digest
    implementation.
Ignoring failure returns of EVP_DigestInit_ex(),
    EVP_DigestInit_ex2(), or EVP_DigestInit() can lead to
    undefined behavior on subsequent calls updating or finalizing the
    EVP_MD_CTX such as the EVP_DigestUpdate() or
    EVP_DigestFinal() functions. The only valid calls on the
    EVP_MD_CTX when initialization fails are calls that attempt another
    initialization of the context or release the context.
The functions EVP_DigestInit(), EVP_DigestFinal()
    and EVP_MD_CTX_copy() are obsolete but are retained to maintain
    compatibility with existing code. New applications should use
    EVP_DigestInit_ex(), EVP_DigestFinal_ex() and
    EVP_MD_CTX_copy_ex() because they can efficiently reuse a digest
    context instead of initializing and cleaning it up on each call and allow
    non default implementations of digests to be specified.
If digest contexts are not cleaned up after use, memory leaks will
    occur.
EVP_MD_CTX_get0_name(), EVP_MD_CTX_get_size(),
    EVP_MD_CTX_get_block_size(), EVP_MD_CTX_get_type(),
    EVP_get_digestbynid() and EVP_get_digestbyobj() are defined as
    macros.
EVP_MD_CTX_ctrl() sends commands to message digests for
    additional configuration or control.
This example digests the data "Test Message\n" and "Hello
  World\n", using the digest name passed on the command line.
 #include <stdio.h>
 #include <string.h>
 #include <openssl/evp.h>
 int main(int argc, char *argv[])
 {
     EVP_MD_CTX *mdctx;
     const EVP_MD *md;
     char mess1[] = "Test Message\n";
     char mess2[] = "Hello World\n";
     unsigned char md_value[EVP_MAX_MD_SIZE];
     unsigned int md_len, i;
     if (argv[1] == NULL) {
         printf("Usage: mdtest digestname\n");
         exit(1);
     }
     md = EVP_get_digestbyname(argv[1]);
     if (md == NULL) {
         printf("Unknown message digest %s\n", argv[1]);
         exit(1);
     }
     mdctx = EVP_MD_CTX_new();
     if (!EVP_DigestInit_ex2(mdctx, md, NULL)) {
         printf("Message digest initialization failed.\n");
         EVP_MD_CTX_free(mdctx);
         exit(1);
     }
     if (!EVP_DigestUpdate(mdctx, mess1, strlen(mess1))) {
         printf("Message digest update failed.\n");
         EVP_MD_CTX_free(mdctx);
         exit(1);
     }
     if (!EVP_DigestUpdate(mdctx, mess2, strlen(mess2))) {
         printf("Message digest update failed.\n");
         EVP_MD_CTX_free(mdctx);
         exit(1);
     }
     if (!EVP_DigestFinal_ex(mdctx, md_value, &md_len)) {
         printf("Message digest finalization failed.\n");
         EVP_MD_CTX_free(mdctx);
         exit(1);
     }
     EVP_MD_CTX_free(mdctx);
     printf("Digest is: ");
     for (i = 0; i < md_len; i++)
         printf("%02x", md_value[i]);
     printf("\n");
     exit(0);
 }
EVP_MD_meth_new(3), openssl-dgst(1), evp(7),
  OSSL_PROVIDER(3), OSSL_PARAM(3), property(7),
  "ALGORITHM FETCHING" in crypto(7), provider-digest(7),
  life_cycle-digest(7)
The full list of digest algorithms are provided below.
EVP_blake2b512(3), EVP_md2(3), EVP_md4(3),
    EVP_md5(3), EVP_mdc2(3), EVP_ripemd160(3),
    EVP_sha1(3), EVP_sha224(3), EVP_sha3_224(3),
    EVP_sm3(3), EVP_whirlpool(3)
The EVP_MD_CTX_create() and EVP_MD_CTX_destroy() functions were
  renamed to EVP_MD_CTX_new() and EVP_MD_CTX_free() in OpenSSL
  1.1.0, respectively.
The link between digests and signing algorithms was fixed in
    OpenSSL 1.0 and later, so now EVP_sha1() can be used with RSA and
    DSA.
The EVP_dss1() function was removed in OpenSSL 1.1.0.
The EVP_MD_CTX_set_pkey_ctx() function was added in OpenSSL
    1.1.1.
The EVP_Q_digest(), EVP_DigestInit_ex2(),
    EVP_MD_fetch(), EVP_MD_free(), EVP_MD_up_ref(),
    EVP_MD_get_params(), EVP_MD_CTX_set_params(),
    EVP_MD_CTX_get_params(), EVP_MD_gettable_params(),
    EVP_MD_gettable_ctx_params(), EVP_MD_settable_ctx_params(),
    EVP_MD_CTX_settable_params() and EVP_MD_CTX_gettable_params()
    functions were added in OpenSSL 3.0.
The EVP_MD_type(), EVP_MD_nid(),
    EVP_MD_name(), EVP_MD_pkey_type(), EVP_MD_size(),
    EVP_MD_block_size(), EVP_MD_flags(), EVP_MD_CTX_size(),
    EVP_MD_CTX_block_size(), EVP_MD_CTX_type(), and
    EVP_MD_CTX_md_data() functions were renamed to include
    "get" or
    "get0" in their names in OpenSSL 3.0,
    respectively. The old names are kept as non-deprecated alias macros.
The EVP_MD_CTX_md() function was deprecated in OpenSSL 3.0;
    use EVP_MD_CTX_get0_md() instead. EVP_MD_CTX_update_fn() and
    EVP_MD_CTX_set_update_fn() were deprecated in OpenSSL 3.0.
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License").
    You may not use this file except in compliance with the License. You can
    obtain a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.