vendor/openssl-src/openssl/doc/man3/EVP_DigestInit.pod - toolchain/rustc - Git at Google

 =pod

 =head1 NAME

 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_flags,
 EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags,
 EVP_Digest, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,
 EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal,
 EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_flags,
 EVP_MD_CTX_md, EVP_MD_CTX_type, EVP_MD_CTX_size, EVP_MD_CTX_block_size,
 EVP_MD_CTX_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_pkey_ctx, EVP_MD_CTX_set_pkey_ctx - EVP digest routines

 =head1 SYNOPSIS

  #include <openssl/evp.h>

  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);
  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_Digest(const void *data, size_t count, unsigned char *md,
                 unsigned int *size, const EVP_MD *type, ENGINE *impl);
  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);

  int EVP_MD_type(const EVP_MD *md);
  int EVP_MD_pkey_type(const EVP_MD *md);
  int EVP_MD_size(const EVP_MD *md);
  int EVP_MD_block_size(const EVP_MD *md);
  unsigned long EVP_MD_flags(const EVP_MD *md);

  const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
  int EVP_MD_CTX_size(const EVP_MD_CTX *ctx);
  int EVP_MD_CTX_block_size(const EVP_MD_CTX *ctx);
  int EVP_MD_CTX_type(const EVP_MD_CTX *ctx);
  void *EVP_MD_CTX_md_data(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));

  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_pkey_ctx(const EVP_MD_CTX *ctx);
  void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);

 =head1 DESCRIPTION

 The EVP digest routines are a high-level interface to message digests,
 and should be used instead of the cipher-specific functions.

 =over 4

 =item EVP_MD_CTX_new()

 Allocates and returns a digest context.

 =item EVP_MD_CTX_reset()

 Resets the digest context B<ctx>.  This can be used to reuse an already
 existing context.

 =item EVP_MD_CTX_free()

 Cleans up digest context B<ctx> and frees up the space allocated to it.

 =item EVP_MD_CTX_ctrl()

 Performs digest-specific control actions on context B<ctx>. The control command
 is indicated in B<cmd> and any additional arguments in B<p1> and B<p2>.
 EVP_MD_CTX_ctrl() must be called after EVP_DigestInit_ex(). Other restrictions
 may apply depending on the control type and digest implementation.
 See L</CONTROLS> below for more information.

 =item EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(), EVP_MD_CTX_test_flags()

 Sets, clears and tests B<ctx> flags.  See L</FLAGS> below for more information.

 =item EVP_Digest()

 A wrapper around the Digest Init_ex, Update and Final_ex functions.
 Hashes B<count> bytes of data at B<data> using a digest B<type> from ENGINE
 B<impl>. The digest value is placed in B<md> and its length is written at B<size>
 if the pointer is not NULL. At most B<EVP_MAX_MD_SIZE> bytes will be written.
 If B<impl> is NULL the default implementation of digest B<type> is used.

 =item EVP_DigestInit_ex()

 Sets up digest context B<ctx> to use a digest B<type> from ENGINE B<impl>.
 B<type> will typically be supplied by a function such as EVP_sha1().  If
 B<impl> is NULL then the default implementation of digest B<type> is used.

 =item EVP_DigestUpdate()

 Hashes B<cnt> bytes of data at B<d> into the digest context B<ctx>. This
 function can be called several times on the same B<ctx> to hash additional
 data.

 =item EVP_DigestFinal_ex()

 Retrieves the digest value from B<ctx> and places it in B<md>. If the B<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 B<s>, at most
 B<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_ex() can be called to initialize a new digest operation.

 =item EVP_DigestFinalXOF()

 Interfaces to extendable-output functions, XOFs, such as SHAKE128 and SHAKE256.
 It retrieves the digest value from B<ctx> and places it in B<len>-sized <B>md.
 After calling this function no additional calls to EVP_DigestUpdate() can be
 made, but EVP_DigestInit_ex() can be called to initialize a new operation.

 =item EVP_MD_CTX_copy_ex()

 Can be used to copy the message digest state from B<in> to B<out>. This is
 useful if large amounts of data are to be hashed which only differ in the last
 few bytes.

 =item EVP_DigestInit()

 Behaves in the same way as EVP_DigestInit_ex() except it always uses the
 default digest implementation and calls EVP_MD_CTX_reset().

 =item EVP_DigestFinal()

 Similar to EVP_DigestFinal_ex() except the digest context B<ctx> is
 automatically cleaned up.

 =item EVP_MD_CTX_copy()

 Similar to EVP_MD_CTX_copy_ex() except the destination B<out> does not have to
 be initialized.

 =item EVP_MD_size(),
 EVP_MD_CTX_size()

 Return the size of the message digest when passed an B<EVP_MD> or an
 B<EVP_MD_CTX> structure, i.e. the size of the hash.

 =item EVP_MD_block_size(),
 EVP_MD_CTX_block_size()

 Return the block size of the message digest when passed an B<EVP_MD> or an
 B<EVP_MD_CTX> structure.

 =item EVP_MD_type(),
 EVP_MD_CTX_type()

 Return the NID of the OBJECT IDENTIFIER representing the given message digest
 when passed an B<EVP_MD> structure.  For example, C<EVP_MD_type(EVP_sha1())>
 returns B<NID_sha1>. This function is normally used when setting ASN1 OIDs.

 =item EVP_MD_CTX_md_data()

 Return the digest method private data for the passed B<EVP_MD_CTX>.
 The space is allocated by OpenSSL and has the size originally set with
 EVP_MD_meth_set_app_datasize().

 =item EVP_MD_CTX_md()

 Returns the B<EVP_MD> structure corresponding to the passed B<EVP_MD_CTX>.

 =item EVP_MD_CTX_set_update_fn()

 Sets the update function for B<ctx> to B<update>.
 This is the function that is called by EVP_DigestUpdate. If not set, the
 update function from the B<EVP_MD> type specified at initialization is used.

 =item EVP_MD_CTX_update_fn()

 Returns the update function for B<ctx>.

 =item EVP_MD_flags()

 Returns the B<md> flags. Note that these are different from the B<EVP_MD_CTX>
 ones. See L<EVP_MD_meth_set_flags(3)> for more information.

 =item EVP_MD_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
 B<NID_sha1WithRSAEncryption>. Since digests and signature algorithms are no
 longer linked this function is only retained for compatibility reasons.

 =item EVP_md_null()

 A "null" message digest that does nothing: i.e. the hash it returns is of zero
 length.

 =item EVP_get_digestbyname(),
 EVP_get_digestbynid(),
 EVP_get_digestbyobj()

 Returns an B<EVP_MD> structure when passed a digest name, a digest B<NID> or an
 B<ASN1_OBJECT> structure respectively.

 =item EVP_MD_CTX_pkey_ctx()

 Returns the B<EVP_PKEY_CTX> assigned to B<ctx>. The returned pointer should not
 be freed by the caller.

 =item EVP_MD_CTX_set_pkey_ctx()

 Assigns an B<EVP_PKEY_CTX> to B<EVP_MD_CTX>. This is usually used to provide
 a customized B<EVP_PKEY_CTX> to L<EVP_DigestSignInit(3)> or
 L<EVP_DigestVerifyInit(3)>. The B<pctx> passed to this function should be freed
 by the caller. A NULL B<pctx> pointer is also allowed to clear the B<EVP_PKEY_CTX>
 assigned to B<ctx>. In such case, freeing the cleared B<EVP_PKEY_CTX> or not
 depends on how the B<EVP_PKEY_CTX> is created.

 =back

 =head1 CONTROLS

 EVP_MD_CTX_ctrl() can be used to send the following standard controls:

 =over 4

 =item 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 B<p2>.

 =item EVP_MD_CTRL_XOF_LEN

 This control sets the digest length for extendable output functions to B<p1>.
 Sending this control directly should not be necessary, the use of
 C<EVP_DigestFinalXOF()> is preferred.
 Currently used by SHAKE.

 =back

 =head1 FLAGS

 EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags() and EVP_MD_CTX_test_flags()
 can be used the manipulate and test these B<EVP_MD_CTX> flags:

 =over 4

 =item EVP_MD_CTX_FLAG_ONESHOT

 This flag instructs the digest to optimize for one update only, if possible.

 =for comment EVP_MD_CTX_FLAG_CLEANED is internal, don't mention it

 =for comment EVP_MD_CTX_FLAG_REUSE is internal, don't mention it

 =for comment We currently avoid documenting flags that are only bit holder:
 EVP_MD_CTX_FLAG_NON_FIPS_ALLOW, EVP_MD_CTX_FLAGS_PAD_*

 =item EVP_MD_CTX_FLAG_NO_INIT

 This flag instructs EVP_DigestInit() and similar not to initialise the
 implementation specific data.

 =item 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.

 =back

 =head1 RETURN VALUES

 =over 4

 =item EVP_DigestInit_ex(),
 EVP_DigestUpdate(),
 EVP_DigestFinal_ex()

 Returns 1 for
 success and 0 for failure.

 =item EVP_MD_CTX_ctrl()

 Returns 1 if successful or 0 for failure.

 =item EVP_MD_CTX_copy_ex()

 Returns 1 if successful or 0 for failure.

 =item EVP_MD_type(),
 EVP_MD_pkey_type()

 Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none
 exists.

 =item EVP_MD_size(),
 EVP_MD_block_size(),
 EVP_MD_CTX_size(),
 EVP_MD_CTX_block_size()

 Returns the digest or block size in bytes.

 =item EVP_md_null()

 Returns a pointer to the B<EVP_MD> structure of the "null" message digest.

 =item EVP_get_digestbyname(),
 EVP_get_digestbynid(),
 EVP_get_digestbyobj()

 Returns either an B<EVP_MD> structure or NULL if an error occurs.

 =item EVP_MD_CTX_set_pkey_ctx()

 This function has no return value.

 =back

 =head1 NOTES

 The B<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 L<EVP_sha256(3)>) or the SHA-3
 digest algorithms (such as L<EVP_sha3_512(3)>). The other digest algorithms
 are still in common use.

 For most applications the B<impl> parameter to EVP_DigestInit_ex() will be
 set to NULL to use the default digest implementation.

 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_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_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.

 =head1 EXAMPLES

 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();
      EVP_DigestInit_ex(mdctx, md, NULL);
      EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
      EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
      EVP_DigestFinal_ex(mdctx, md_value, &md_len);
      EVP_MD_CTX_free(mdctx);

      printf("Digest is: ");
      for (i = 0; i < md_len; i++)
          printf("%02x", md_value[i]);
      printf("\n");

      exit(0);
  }

 =head1 SEE ALSO

 L<EVP_MD_meth_new(3)>,
 L<dgst(1)>,
 L<evp(7)>

 The full list of digest algorithms are provided below.

 L<EVP_blake2b512(3)>,
 L<EVP_md2(3)>,
 L<EVP_md4(3)>,
 L<EVP_md5(3)>,
 L<EVP_mdc2(3)>,
 L<EVP_ripemd160(3)>,
 L<EVP_sha1(3)>,
 L<EVP_sha224(3)>,
 L<EVP_sha3_224(3)>,
 L<EVP_sm3(3)>,
 L<EVP_whirlpool(3)>

 =head1 HISTORY

 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 1.1.1.

 =head1 COPYRIGHT

 Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

 Licensed under the OpenSSL license (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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

	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_flags,
	EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags,
	EVP_Digest, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,
	EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal,
	EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_flags,
	EVP_MD_CTX_md, EVP_MD_CTX_type, EVP_MD_CTX_size, EVP_MD_CTX_block_size,
	EVP_MD_CTX_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_pkey_ctx, EVP_MD_CTX_set_pkey_ctx - EVP digest routines

	=head1 SYNOPSIS

	#include <openssl/evp.h>

	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);
	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_Digest(const void data, size_t count, unsigned char md,
	unsigned int size, const EVP_MD type, ENGINE *impl);
	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);

	int EVP_MD_type(const EVP_MD *md);
	int EVP_MD_pkey_type(const EVP_MD *md);
	int EVP_MD_size(const EVP_MD *md);
	int EVP_MD_block_size(const EVP_MD *md);
	unsigned long EVP_MD_flags(const EVP_MD *md);

	const EVP_MD EVP_MD_CTX_md(const EVP_MD_CTX ctx);
	int EVP_MD_CTX_size(const EVP_MD_CTX *ctx);
	int EVP_MD_CTX_block_size(const EVP_MD_CTX *ctx);
	int EVP_MD_CTX_type(const EVP_MD_CTX *ctx);
	void EVP_MD_CTX_md_data(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));

	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_pkey_ctx(const EVP_MD_CTX ctx);
	void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX ctx, EVP_PKEY_CTX pctx);

	=head1 DESCRIPTION

	The EVP digest routines are a high-level interface to message digests,
	and should be used instead of the cipher-specific functions.

	=over 4

	=item EVP_MD_CTX_new()

	Allocates and returns a digest context.

	=item EVP_MD_CTX_reset()

	Resets the digest context B<ctx>. This can be used to reuse an already
	existing context.

	=item EVP_MD_CTX_free()

	Cleans up digest context B<ctx> and frees up the space allocated to it.

	=item EVP_MD_CTX_ctrl()

	Performs digest-specific control actions on context B<ctx>. The control command
	is indicated in B<cmd> and any additional arguments in B<p1> and B<p2>.
	EVP_MD_CTX_ctrl() must be called after EVP_DigestInit_ex(). Other restrictions
	may apply depending on the control type and digest implementation.
	See L</CONTROLS> below for more information.

	=item EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(), EVP_MD_CTX_test_flags()

	Sets, clears and tests B<ctx> flags. See L</FLAGS> below for more information.

	=item EVP_Digest()

	A wrapper around the Digest Init_ex, Update and Final_ex functions.
	Hashes B<count> bytes of data at B<data> using a digest B<type> from ENGINE
	B<impl>. The digest value is placed in B<md> and its length is written at B<size>
	if the pointer is not NULL. At most B<EVP_MAX_MD_SIZE> bytes will be written.
	If B<impl> is NULL the default implementation of digest B<type> is used.

	=item EVP_DigestInit_ex()

	Sets up digest context B<ctx> to use a digest B<type> from ENGINE B<impl>.
	B<type> will typically be supplied by a function such as EVP_sha1(). If
	B<impl> is NULL then the default implementation of digest B<type> is used.

	=item EVP_DigestUpdate()

	Hashes B<cnt> bytes of data at B<d> into the digest context B<ctx>. This
	function can be called several times on the same B<ctx> to hash additional
	data.

	=item EVP_DigestFinal_ex()

	Retrieves the digest value from B<ctx> and places it in B<md>. If the B<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 B<s>, at most
	B<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_ex() can be called to initialize a new digest operation.

	=item EVP_DigestFinalXOF()

	Interfaces to extendable-output functions, XOFs, such as SHAKE128 and SHAKE256.
	It retrieves the digest value from B<ctx> and places it in B<len>-sized <B>md.
	After calling this function no additional calls to EVP_DigestUpdate() can be
	made, but EVP_DigestInit_ex() can be called to initialize a new operation.

	=item EVP_MD_CTX_copy_ex()

	Can be used to copy the message digest state from B<in> to B<out>. This is
	useful if large amounts of data are to be hashed which only differ in the last
	few bytes.

	=item EVP_DigestInit()

	Behaves in the same way as EVP_DigestInit_ex() except it always uses the
	default digest implementation and calls EVP_MD_CTX_reset().

	=item EVP_DigestFinal()

	Similar to EVP_DigestFinal_ex() except the digest context B<ctx> is
	automatically cleaned up.

	=item EVP_MD_CTX_copy()

	Similar to EVP_MD_CTX_copy_ex() except the destination B<out> does not have to
	be initialized.

	=item EVP_MD_size(),
	EVP_MD_CTX_size()

	Return the size of the message digest when passed an B<EVP_MD> or an
	B<EVP_MD_CTX> structure, i.e. the size of the hash.

	=item EVP_MD_block_size(),
	EVP_MD_CTX_block_size()

	Return the block size of the message digest when passed an B<EVP_MD> or an
	B<EVP_MD_CTX> structure.

	=item EVP_MD_type(),
	EVP_MD_CTX_type()

	Return the NID of the OBJECT IDENTIFIER representing the given message digest
	when passed an B<EVP_MD> structure. For example, C<EVP_MD_type(EVP_sha1())>
	returns B<NID_sha1>. This function is normally used when setting ASN1 OIDs.

	=item EVP_MD_CTX_md_data()

	Return the digest method private data for the passed B<EVP_MD_CTX>.
	The space is allocated by OpenSSL and has the size originally set with
	EVP_MD_meth_set_app_datasize().

	=item EVP_MD_CTX_md()

	Returns the B<EVP_MD> structure corresponding to the passed B<EVP_MD_CTX>.

	=item EVP_MD_CTX_set_update_fn()

	Sets the update function for B<ctx> to B<update>.
	This is the function that is called by EVP_DigestUpdate. If not set, the
	update function from the B<EVP_MD> type specified at initialization is used.

	=item EVP_MD_CTX_update_fn()

	Returns the update function for B<ctx>.

	=item EVP_MD_flags()

	Returns the B<md> flags. Note that these are different from the B<EVP_MD_CTX>
	ones. See L<EVP_MD_meth_set_flags(3)> for more information.

	=item EVP_MD_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
	B<NID_sha1WithRSAEncryption>. Since digests and signature algorithms are no
	longer linked this function is only retained for compatibility reasons.

	=item EVP_md_null()

	A "null" message digest that does nothing: i.e. the hash it returns is of zero
	length.

	=item EVP_get_digestbyname(),
	EVP_get_digestbynid(),
	EVP_get_digestbyobj()

	Returns an B<EVP_MD> structure when passed a digest name, a digest B<NID> or an
	B<ASN1_OBJECT> structure respectively.

	=item EVP_MD_CTX_pkey_ctx()

	Returns the B<EVP_PKEY_CTX> assigned to B<ctx>. The returned pointer should not
	be freed by the caller.

	=item EVP_MD_CTX_set_pkey_ctx()

	Assigns an B<EVP_PKEY_CTX> to B<EVP_MD_CTX>. This is usually used to provide
	a customized B<EVP_PKEY_CTX> to L<EVP_DigestSignInit(3)> or
	L<EVP_DigestVerifyInit(3)>. The B<pctx> passed to this function should be freed
	by the caller. A NULL B<pctx> pointer is also allowed to clear the B<EVP_PKEY_CTX>
	assigned to B<ctx>. In such case, freeing the cleared B<EVP_PKEY_CTX> or not
	depends on how the B<EVP_PKEY_CTX> is created.

	=back

	=head1 CONTROLS

	EVP_MD_CTX_ctrl() can be used to send the following standard controls:

	=over 4

	=item 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 B<p2>.

	=item EVP_MD_CTRL_XOF_LEN

	This control sets the digest length for extendable output functions to B<p1>.
	Sending this control directly should not be necessary, the use of
	C<EVP_DigestFinalXOF()> is preferred.
	Currently used by SHAKE.

	=back

	=head1 FLAGS

	EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags() and EVP_MD_CTX_test_flags()
	can be used the manipulate and test these B<EVP_MD_CTX> flags:

	=over 4

	=item EVP_MD_CTX_FLAG_ONESHOT

	This flag instructs the digest to optimize for one update only, if possible.

	=for comment EVP_MD_CTX_FLAG_CLEANED is internal, don't mention it

	=for comment EVP_MD_CTX_FLAG_REUSE is internal, don't mention it

	=for comment We currently avoid documenting flags that are only bit holder:
	EVP_MD_CTX_FLAG_NON_FIPS_ALLOW, EVP_MD_CTX_FLAGS_PAD_*

	=item EVP_MD_CTX_FLAG_NO_INIT

	This flag instructs EVP_DigestInit() and similar not to initialise the
	implementation specific data.

	=item 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.

	=back

	=head1 RETURN VALUES

	=over 4

	=item EVP_DigestInit_ex(),
	EVP_DigestUpdate(),
	EVP_DigestFinal_ex()

	Returns 1 for
	success and 0 for failure.

	=item EVP_MD_CTX_ctrl()

	Returns 1 if successful or 0 for failure.

	=item EVP_MD_CTX_copy_ex()

	Returns 1 if successful or 0 for failure.

	=item EVP_MD_type(),
	EVP_MD_pkey_type()

	Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none
	exists.

	=item EVP_MD_size(),
	EVP_MD_block_size(),
	EVP_MD_CTX_size(),
	EVP_MD_CTX_block_size()

	Returns the digest or block size in bytes.

	=item EVP_md_null()

	Returns a pointer to the B<EVP_MD> structure of the "null" message digest.

	=item EVP_get_digestbyname(),
	EVP_get_digestbynid(),
	EVP_get_digestbyobj()

	Returns either an B<EVP_MD> structure or NULL if an error occurs.

	=item EVP_MD_CTX_set_pkey_ctx()

	This function has no return value.

	=back

	=head1 NOTES

	The B<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 L<EVP_sha256(3)>) or the SHA-3
	digest algorithms (such as L<EVP_sha3_512(3)>). The other digest algorithms
	are still in common use.

	For most applications the B<impl> parameter to EVP_DigestInit_ex() will be
	set to NULL to use the default digest implementation.

	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_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_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.

	=head1 EXAMPLES

	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();
	EVP_DigestInit_ex(mdctx, md, NULL);
	EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
	EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
	EVP_DigestFinal_ex(mdctx, md_value, &md_len);
	EVP_MD_CTX_free(mdctx);

	printf("Digest is: ");
	for (i = 0; i < md_len; i++)
	printf("%02x", md_value[i]);
	printf("\n");

	exit(0);
	}

	=head1 SEE ALSO

	L<EVP_MD_meth_new(3)>,
	L<dgst(1)>,
	L<evp(7)>

	The full list of digest algorithms are provided below.

	L<EVP_blake2b512(3)>,
	L<EVP_md2(3)>,
	L<EVP_md4(3)>,
	L<EVP_md5(3)>,
	L<EVP_mdc2(3)>,
	L<EVP_ripemd160(3)>,
	L<EVP_sha1(3)>,
	L<EVP_sha224(3)>,
	L<EVP_sha3_224(3)>,
	L<EVP_sm3(3)>,
	L<EVP_whirlpool(3)>

	=head1 HISTORY

	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 1.1.1.

	=head1 COPYRIGHT

	Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

	Licensed under the OpenSSL license (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
	L<https://www.openssl.org/source/license.html>.

	=cut