.\"	$OpenBSD: EVP_DigestInit.3,v 1.6 2017/03/25 17:54:04 schwarze Exp $
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.Dd $Mdocdate: March 25 2017 $
.Dt EVP_DIGESTINIT 3
.Os
.Sh NAME
.Nm EVP_MD_CTX_init ,
.Nm EVP_MD_CTX_create ,
.Nm EVP_MD_CTX_ctrl ,
.Nm EVP_DigestInit_ex ,
.Nm EVP_DigestUpdate ,
.Nm EVP_DigestFinal_ex ,
.Nm EVP_MD_CTX_cleanup ,
.Nm EVP_MD_CTX_destroy ,
.Nm EVP_MD_CTX_copy_ex ,
.Nm EVP_DigestInit ,
.Nm EVP_DigestFinal ,
.Nm EVP_MD_CTX_copy ,
.Nm EVP_MAX_MD_SIZE ,
.Nm EVP_MD_type ,
.Nm EVP_MD_pkey_type ,
.Nm EVP_MD_size ,
.Nm EVP_MD_block_size ,
.Nm EVP_MD_CTX_md ,
.Nm EVP_MD_CTX_size ,
.Nm EVP_MD_CTX_block_size ,
.Nm EVP_MD_CTX_type ,
.Nm EVP_md_null ,
.Nm EVP_md2 ,
.Nm EVP_md5 ,
.Nm EVP_md5_sha1 ,
.Nm EVP_sha1 ,
.Nm EVP_sha224 ,
.Nm EVP_sha256 ,
.Nm EVP_sha384 ,
.Nm EVP_sha512 ,
.Nm EVP_dss ,
.Nm EVP_dss1 ,
.Nm EVP_ripemd160 ,
.Nm EVP_get_digestbyname ,
.Nm EVP_get_digestbynid ,
.Nm EVP_get_digestbyobj
.Nd EVP digest routines
.Sh SYNOPSIS
.In openssl/evp.h
.Ft void
.Fo EVP_MD_CTX_init
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft EVP_MD_CTX *
.Fn EVP_MD_CTX_create void
.Ft void
.Fo EVP_MD_CTX_ctrl
.Fa "EVP_MD_CTX *ctx"
.Fa "int cmd"
.Fa "int p1"
.Fa "void* p2"
.Fc
.Ft int
.Fo EVP_DigestInit_ex
.Fa "EVP_MD_CTX *ctx"
.Fa "const EVP_MD *type"
.Fa "ENGINE *impl"
.Fc
.Ft int
.Fo EVP_DigestUpdate
.Fa "EVP_MD_CTX *ctx"
.Fa "const void *d"
.Fa "size_t cnt"
.Fc
.Ft int
.Fo EVP_DigestFinal_ex
.Fa "EVP_MD_CTX *ctx"
.Fa "unsigned char *md"
.Fa "unsigned int *s"
.Fc
.Ft int
.Fo EVP_MD_CTX_cleanup
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft void
.Fo EVP_MD_CTX_destroy
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft int
.Fo EVP_MD_CTX_copy_ex
.Fa "EVP_MD_CTX *out"
.Fa "const EVP_MD_CTX *in"
.Fc
.Ft int
.Fo EVP_DigestInit
.Fa "EVP_MD_CTX *ctx"
.Fa "const EVP_MD *type"
.Fc
.Ft int
.Fo EVP_DigestFinal
.Fa "EVP_MD_CTX *ctx"
.Fa "unsigned char *md"
.Fa "unsigned int *s"
.Fc
.Ft int
.Fo EVP_MD_CTX_copy
.Fa "EVP_MD_CTX *out"
.Fa "EVP_MD_CTX *in"
.Fc
.Fd #define EVP_MAX_MD_SIZE 64	/* SHA512 */
.Ft int
.Fo EVP_MD_type
.Fa "const EVP_MD *md"
.Fc
.Ft int
.Fo EVP_MD_pkey_type
.Fa "const EVP_MD *md"
.Fc
.Ft int
.Fo EVP_MD_size
.Fa "const EVP_MD *md"
.Fc
.Ft int
.Fo EVP_MD_block_size
.Fa "const EVP_MD *md"
.Fc
.Ft const EVP_MD *
.Fo EVP_MD_CTX_md
.Fa "const EVP_MD_CTX *ctx"
.Fc
.Ft int
.Fo EVP_MD_CTX_size
.Fa "const EVP_MD *ctx"
.Fc
.Ft int
.Fo EVP_MD_CTX_block_size
.Fa "const EVP_MD *ctx"
.Fc
.Ft int
.Fo EVP_MD_CTX_type
.Fa "const EVP_MD *ctx"
.Fc
.Ft const EVP_MD *
.Fn EVP_md_null void
.Ft const EVP_MD *
.Fn EVP_md2 void
.Ft const EVP_MD *
.Fn EVP_md5 void
.Ft const EVP_MD *
.Fn EVP_md5_sha1 void
.Ft const EVP_MD *
.Fn EVP_sha1 void
.Ft const EVP_MD *
.Fn EVP_sha224 void
.Ft const EVP_MD *
.Fn EVP_sha256 void
.Ft const EVP_MD *
.Fn EVP_sha384 void
.Ft const EVP_MD *
.Fn EVP_sha512 void
.Ft const EVP_MD *
.Fn EVP_dss void
.Ft const EVP_MD *
.Fn EVP_dss1 void
.Ft const EVP_MD *
.Fn EVP_ripemd160 void
.Ft const EVP_MD *
.Fo EVP_get_digestbyname
.Fa "const char *name"
.Fc
.Ft const EVP_MD *
.Fo EVP_get_digestbynid
.Fa "int type"
.Fc
.Ft const EVP_MD *
.Fo EVP_get_digestbyobj
.Fa "const ASN1_OBJECT *o"
.Fc
.Sh DESCRIPTION
The EVP digest routines are a high level interface to message digests.
.Pp
.Fn EVP_MD_CTX_init
initializes the digest context
.Fa ctx .
.Pp
.Fn EVP_MD_CTX_create
allocates, initializes, and returns a digest context.
.Pp
.Fn EVP_MD_CTX_ctrl
performs digest-specific control actions on the context
.Fa ctx .
.Pp
.Fn EVP_DigestInit_ex
sets up digest context
.Fa ctx
to use a digest
.Fa type
from
.Vt ENGINE
.Fa impl .
.Fa ctx
must be initialized before calling this function.
.Fa type
will typically be supplied by a function such as
.Fn EVP_sha1 .
If
.Fa impl
is
.Dv NULL ,
then the default implementation of digest
.Fa type
is used.
.Pp
.Fn EVP_DigestUpdate
hashes
.Fa cnt
bytes of data at
.Fa d
into the digest context
.Fa ctx .
This function can be called several times on the same
.Fa ctx
to hash additional data.
.Pp
.Fn EVP_DigestFinal_ex
retrieves the digest value from
.Fa ctx
and places it in
.Fa md .
If the
.Fa s
parameter is not
.Dv NULL ,
then the number of bytes of data written (i.e. the length of the
digest) will be written to the integer at
.Fa s ;
at most
.Dv EVP_MAX_MD_SIZE
bytes will be written.
After calling
.Fn EVP_DigestFinal_ex ,
no additional calls to
.Fn EVP_DigestUpdate
can be made, but
.Fn EVP_DigestInit_ex
can be called to initialize a new digest operation.
.Pp
.Fn EVP_MD_CTX_cleanup
cleans up the digest context
.Fa ctx .
It should be called after a digest context is no longer needed.
.Pp
.Fn EVP_MD_CTX_destroy
cleans up the digest context
.Fa ctx
and frees up the space allocated to it.
It should be called only on a context created using
.Fn EVP_MD_CTX_create .
.Pp
.Fn EVP_MD_CTX_copy_ex
can be used to copy the message digest state from
.Fa in
to
.Fa out .
This is useful if large amounts of data are to be hashed which only
differ in the last few bytes.
.Fa out
must be initialized before calling this function.
.Pp
.Fn EVP_DigestInit
behaves in the same way as
.Fn EVP_DigestInit_ex
except the passed context
.Fa ctx
does not have to be initialized, and it always uses the default digest
implementation.
.Pp
.Fn EVP_DigestFinal
is similar to
.Fn EVP_DigestFinal_ex
except the digest context
.Fa ctx
is automatically cleaned up.
.Pp
.Fn EVP_MD_CTX_copy
is similar to
.Fn EVP_MD_CTX_copy_ex
except the destination
.Fa out
does not have to be initialized.
.Pp
.Fn EVP_MD_size
and
.Fn EVP_MD_CTX_size
return the size of the message digest when passed an
.Vt EVP_MD
or an
.Vt EVP_MD_CTX
structure, i.e. the size of the hash.
.Pp
.Fn EVP_MD_block_size
and
.Fn EVP_MD_CTX_block_size
return the block size of the message digest when passed an
.Vt EVP_MD
or an
.Vt EVP_MD_CTX
structure.
.Pp
.Fn EVP_MD_type
and
.Fn EVP_MD_CTX_type
return the NID of the OBJECT IDENTIFIER representing the given message
digest when passed an
.Vt EVP_MD
structure.
For example
.Fn EVP_MD_type EVP_sha1()
returns
.Dv NID_sha1 .
This function is normally used when setting ASN.1 OIDs.
.Pp
.Fn EVP_MD_CTX_md
returns the
.Vt EVP_MD
structure corresponding to the passed
.Vt EVP_MD_CTX .
.Pp
.Fn EVP_MD_pkey_type
returns the NID of the public key signing algorithm associated with this
digest.
For example
.Fn EVP_sha1
is associated with RSA so this will return
.Dv NID_sha1WithRSAEncryption .
Since digests and signature algorithms are no longer linked this
function is only retained for compatibility reasons.
.Pp
.Fn EVP_md2 ,
.Fn EVP_md5 ,
.Fn EVP_sha1 ,
.Fn EVP_sha224 ,
.Fn EVP_sha256 ,
.Fn EVP_sha384 ,
.Fn EVP_sha512 ,
and
.Fn EVP_ripemd160
return
.Vt EVP_MD
structures for the MD2, MD5, SHA1, SHA224, SHA256, SHA384, SHA512 and
RIPEMD160 digest algorithms respectively.
.Pp
.Fn EVP_md5_sha1
returns an
.Vt EVP_MD
structure that provides concatenated MD5 and SHA1 message digests.
.Pp
.Fn EVP_dss
and
.Fn EVP_dss1
return
.Vt EVP_MD
structures for SHA1 digest algorithms but using DSS (DSA) for the
signature algorithm.
Note: there is no need to use these pseudo-digests in OpenSSL 1.0.0 and
later; they are however retained for compatibility.
.Pp
.Fn EVP_md_null
is a "null" message digest that does nothing:
i.e. the hash it returns is of zero length.
.Pp
.Fn EVP_get_digestbyname ,
.Fn EVP_get_digestbynid ,
and
.Fn EVP_get_digestbyobj
return an
.Vt EVP_MD
structure when passed a digest name, a digest NID, or an ASN1_OBJECT
structure respectively.
The digest table must be initialized using, for example,
.Xr OpenSSL_add_all_digests 3
for these functions to work.
.Pp
.Fn EVP_MD_CTX_size ,
.Fn EVP_MD_CTX_block_size ,
.Fn EVP_MD_CTX_type ,
.Fn EVP_get_digestbynid ,
and
.Fn EVP_get_digestbyobj
are implemented as macros.
.Pp
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.
.Pp
New applications should use the SHA2 digest algorithms such as SHA256.
The other digest algorithms are still in common use.
.Pp
For most applications the
.Fa impl
parameter to
.Fn EVP_DigestInit_ex
will be set to NULL to use the default digest implementation.
.Pp
The functions
.Fn EVP_DigestInit ,
.Fn EVP_DigestFinal ,
and
.Fn EVP_MD_CTX_copy
are obsolete but are retained to maintain compatibility with existing
code.
New applications should use
.Fn EVP_DigestInit_ex ,
.Fn EVP_DigestFinal_ex ,
and
.Fn 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.
.Pp
In OpenSSL 0.9.7 and later if digest contexts are not cleaned up after
use memory leaks will occur.
.Pp
Stack allocation of
.Vt EVP_MD_CTX
structures is common, for example:
.Bd -literal -offset indent
EVP_MD_CTX mctx;
EVP_MD_CTX_init(&mctx);
.Ed
.Pp
This will cause binary compatibility issues if the size of
.Vt EVP_MD_CTX
structure changes (this will only happen with a major release of OpenSSL).
Applications wishing to avoid this should use
.Fn EVP_MD_CTX_create
instead:
.Bd -literal -offset indent
EVP_MD_CTX *mctx;
mctx = EVP_MD_CTX_create();
.Ed
.Sh RETURN VALUES
.Fn EVP_MD_CTX_ctrl ,
.Fn EVP_DigestInit_ex ,
.Fn EVP_DigestUpdate ,
.Fn EVP_DigestFinal_ex ,
and
.Fn EVP_MD_CTX_copy_ex
return 1 for success or 0 for failure.
.Pp
.Fn EVP_MD_type ,
.Fn EVP_MD_pkey_type ,
and
.Fn EVP_MD_type
return the NID of the corresponding OBJECT IDENTIFIER or
.Dv NID_undef
if none exists.
.Pp
.Fn EVP_MD_size ,
.Fn EVP_MD_block_size ,
.Fn EVP_MD_CTX_size ,
and
.Fn EVP_MD_CTX_block_size
return the digest or block size in bytes.
.Pp
.Fn EVP_md_null ,
.Fn EVP_md2 ,
.Fn EVP_md5 ,
.Fn EVP_md5_sha1 ,
.Fn EVP_sha1 ,
.Fn EVP_dss ,
.Fn EVP_dss1 ,
and
.Fn EVP_ripemd160
return pointers to the corresponding
.Vt EVP_MD
structures.
.Pp
.Fn EVP_get_digestbyname ,
.Fn EVP_get_digestbynid ,
and
.Fn EVP_get_digestbyobj
return either an
.Vt EVP_MD
structure or
.Dv NULL
if an error occurs.
.Sh EXAMPLES
This example digests the data "Test Message\en" and "Hello World\en",
using the digest name passed on the command line.
.Bd -literal -offset indent
#include <stdio.h>
#include <openssl/evp.h>

int
main(int argc, char *argv[])
{
	EVP_MD_CTX *mdctx;
	const EVP_MD *md;
	const char mess1[] = "Test Message\en";
	const char mess2[] = "Hello World\en";
	unsigned char md_value[EVP_MAX_MD_SIZE];
	int md_len, i;

	OpenSSL_add_all_digests();

	if (argc <= 1) {
		printf("Usage: mdtest digestname\en");
		exit(1);
	}

	md = EVP_get_digestbyname(argv[1]);
	if (md == NULL) {
		printf("Unknown message digest %s\en", argv[1]);
		exit(1);
	}

	mdctx = EVP_MD_CTX_create();
	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_destroy(mdctx);

	printf("Digest is: ");
	for(i = 0; i < md_len; i++)
		printf("%02x", md_value[i]);
	printf("\en");
}
.Ed
.Sh SEE ALSO
.Xr evp 3
.Sh HISTORY
.Fn EVP_DigestInit ,
.Fn EVP_DigestUpdate ,
and
.Fn EVP_DigestFinal
are available in all versions of SSLeay and OpenSSL.
.Pp
.Fn EVP_MD_CTX_init ,
.Fn EVP_MD_CTX_create ,
.Fn EVP_MD_CTX_copy_ex ,
.Fn EVP_MD_CTX_cleanup ,
.Fn EVP_MD_CTX_destroy ,
.Fn EVP_DigestInit_ex ,
and
.Fn EVP_DigestFinal_ex
were added in OpenSSL 0.9.7.
.Pp
.Fn EVP_md_null ,
.Fn EVP_md2 ,
.Fn EVP_md5 ,
.Fn EVP_sha1 ,
.Fn EVP_dss ,
.Fn EVP_dss1 ,
and
.Fn EVP_ripemd160
were changed to return truly const
.Vt EVP_MD
pointers in OpenSSL 0.9.7.
.Pp
The link between digests and signing algorithms was fixed in OpenSSL 1.0
and later, so now
.Fn EVP_sha1
can be used with RSA and DSA; there is no need to use
.Fn EVP_dss1
any more.
.Pp
OpenSSL 1.0 and later does not include the MD2 digest algorithm in the
default configuration due to its security weaknesses.