EVP_DIGESTINIT(3) OpenSSL EVP_DIGESTINIT(3)NAME
EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex,
EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_MD_CTX_cleanup,
EVP_MD_CTX_destroy, EVP_MAX_MD_SIZE, EVP_MD_CTX_copy_ex,
EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size,
EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size,
EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_md_null,
EVP_md2, EVP_md5, EVP_sha, EVP_sha1, EVP_dss, EVP_dss1,
EVP_mdc2, EVP_ripemd160, EVP_get_digestbyname,
EVP_get_digestbynid, EVP_get_digestbyobj - EVP digest rou-
tines
SYNOPSIS
#include <openssl/evp.h>
void EVP_MD_CTX_init(EVP_MD_CTX *ctx);
EVP_MD_CTX *EVP_MD_CTX_create(void);
int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
unsigned int *s);
int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);
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);
#define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */
#define EVP_MD_type(e) ((e)->type)
#define EVP_MD_pkey_type(e) ((e)->pkey_type)
#define EVP_MD_size(e) ((e)->md_size)
#define EVP_MD_block_size(e) ((e)->block_size)
#define EVP_MD_CTX_md(e) (e)->digest)
#define EVP_MD_CTX_size(e) EVP_MD_size((e)->digest)
#define EVP_MD_CTX_block_size(e) EVP_MD_block_size((e)->digest)
#define EVP_MD_CTX_type(e) EVP_MD_type((e)->digest)
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EVP_DIGESTINIT(3) OpenSSL EVP_DIGESTINIT(3)
const EVP_MD *EVP_md_null(void);
const EVP_MD *EVP_md2(void);
const EVP_MD *EVP_md5(void);
const EVP_MD *EVP_sha(void);
const EVP_MD *EVP_sha1(void);
const EVP_MD *EVP_dss(void);
const EVP_MD *EVP_dss1(void);
const EVP_MD *EVP_mdc2(void);
const EVP_MD *EVP_ripemd160(void);
const EVP_MD *EVP_get_digestbyname(const char *name);
#define EVP_get_digestbynid(a) EVP_get_digestbyname(OBJ_nid2sn(a))
#define EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))
DESCRIPTION
The EVP digest routines are a high level interface to mes-
sage digests.
EVP_MD_CTX_init() initializes digest contet ctx.
EVP_MD_CTX_create() allocates, initializes and returns a
digest contet.
EVP_DigestInit_ex() sets up digest context ctx to use a dig-
est type from ENGINE impl. ctx must be initialized before
calling this function. type will typically be supplied by a
functionsuch as EVP_sha1(). If impl is NULL then the default
implementation of digest type is used.
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 dig-
est) 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_ex() can
be called to initialize a new digest operation.
EVP_MD_CTX_cleanup() cleans up digest context ctx, it should
be called after a digest context is no longer needed.
EVP_MD_CTX_destroy() cleans up digest context ctx and frees
up the space allocated to it, it should be called only on a
context created using EVP_MD_CTX_create().
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
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EVP_DIGESTINIT(3) OpenSSL EVP_DIGESTINIT(3)
bytes. out must be initialized before calling this function.
EVP_DigestInit() behaves in the same way as
EVP_DigestInit_ex() except the passed context ctx does not
have to be initialized, and it always uses the default dig-
est implementation.
EVP_DigestFinal() is similar to EVP_DigestFinal_ex() except
the digest contet ctx is automatically cleaned up.
EVP_MD_CTX_copy() is similar to EVP_MD_CTX_copy_ex() except
the destination out does not have to be initialized.
EVP_MD_size() and EVP_MD_CTX_size() return the size of the
message digest when passed an EVP_MD or an EVP_MD_CTX struc-
ture, i.e. the size of the hash.
EVP_MD_block_size() and EVP_MD_CTX_block_size() return the
block size of the message digest when passed an EVP_MD or an
EVP_MD_CTX structure.
EVP_MD_type() and EVP_MD_CTX_type() return the NID of the
OBJECT IDENTIFIER representing the given message digest when
passed an EVP_MD structure. For example
EVP_MD_type(EVP_sha1()) returns NID_sha1. This function is
normally used when setting ASN1 OIDs.
EVP_MD_CTX_md() returns the EVP_MD structure corresponding
to the passed EVP_MD_CTX.
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
NID_sha1WithRSAEncryption. This "link" between digests and
signature algorithms may not be retained in future versions
of OpenSSL.
EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_mdc2() and
EVP_ripemd160() return EVP_MD structures for the MD2, MD5,
SHA, SHA1, MDC2 and RIPEMD160 digest algorithms respec-
tively. The associated signature algorithm is RSA in each
case.
EVP_dss() and EVP_dss1() return EVP_MD structures for SHA
and SHA1 digest algorithms but using DSS (DSA) for the sig-
nature algorithm.
EVP_md_null() is a "null" message digest that does nothing:
i.e. the hash it returns is of zero length.
EVP_get_digestbyname(), EVP_get_digestbynid() and
EVP_get_digestbyobj() return an EVP_MD structure when passed
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EVP_DIGESTINIT(3) OpenSSL EVP_DIGESTINIT(3)
a digest name, a digest NID or an ASN1_OBJECT structure
respectively. The digest table must be initialized using,
for example, OpenSSL_add_all_digests() for these functions
to work.
RETURN VALUESEVP_DigestInit_ex(), EVP_DigestUpdate() and
EVP_DigestFinal_ex() return 1 for success and 0 for failure.
EVP_MD_CTX_copy_ex() returns 1 if successful or 0 for
failure.
EVP_MD_type(), EVP_MD_pkey_type() and EVP_MD_type() return
the NID of the corresponding OBJECT IDENTIFIER or NID_undef
if none exists.
EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(e),
EVP_MD_size(), EVP_MD_CTX_block_size() and
EVP_MD_block_size() return the digest or block size in
bytes.
EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(),
EVP_dss(), EVP_dss1(), EVP_mdc2() and EVP_ripemd160() return
pointers to the corresponding EVP_MD structures.
EVP_get_digestbyname(), EVP_get_digestbynid() and
EVP_get_digestbyobj() return either an EVP_MD structure or
NULL if an error occurs.
NOTES
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.
SHA1 is the digest of choice for new applications. 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.
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.
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EVP_DIGESTINIT(3) OpenSSL EVP_DIGESTINIT(3)
In OpenSSL 0.9.7 and later if digest contexts are not
cleaned up after use memory leaks will occur.
EXAMPLE
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 <openssl/evp.h>
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];
int md_len, i;
OpenSSL_add_all_digests();
if(!argv[1]) {
printf("Usage: mdtest digestname\n");
exit(1);
}
md = EVP_get_digestbyname(argv[1]);
if(!md) {
printf("Unknown message digest %s\n", argv[1]);
exit(1);
}
EVP_MD_CTX_init(&mdctx);
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_cleanup(&mdctx);
printf("Digest is: ");
for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);
printf("\n");
}
BUGS
The link between digests and signing algorithms results in a
situation where EVP_sha1() must be used with RSA and
EVP_dss1() must be used with DSS even though they are ident-
ical digests.
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EVP_DIGESTINIT(3) OpenSSL EVP_DIGESTINIT(3)SEE ALSOevp(3), HMAC(3), MD2(3), MD5(3), MDC2(3), RIPEMD160(3),
SHA1(3)HISTORYEVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal()
are available in all versions of SSLeay and OpenSSL.
EVP_MD_CTX_init(), EVP_MD_CTX_create(),
EVP_MD_CTX_copy_ex(), EVP_MD_CTX_cleanup(),
EVP_MD_CTX_destroy(), EVP_DigestInit_ex() and
EVP_DigestFinal_ex() were added in OpenSSL 0.9.7.
EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(),
EVP_dss(), EVP_dss1(), EVP_mdc2() and EVP_ripemd160() were
changed to return truely const EVP_MD * in OpenSSL 0.9.7.
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