EVP_DigestInit(3)
EVP_DigestInit(3) 0.9.6h (2002-07-10) EVP_DigestInit(3)
NAME
EVP_DigestInit, EVP_DigestUpdate, EVP_DigestFinal,
EVP_MAX_MD_SIZE, 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 routines
SYNOPSIS
#include <openssl/evp.h>
void EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
void EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
void EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
unsigned int *s);
#define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */
int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);
#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)
EVP_MD *EVP_md_null(void);
EVP_MD *EVP_md2(void);
EVP_MD *EVP_md5(void);
EVP_MD *EVP_sha(void);
EVP_MD *EVP_sha1(void);
EVP_MD *EVP_dss(void);
EVP_MD *EVP_dss1(void);
EVP_MD *EVP_mdc2(void);
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
message digests.
EVP_DigestInit() initializes a digest context ctx to use a
digest type: this will typically be supplied by a function
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such as EVP_sha1().
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() 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() no additional calls to EVP_DigestUpdate()
can be made, but EVP_DigestInit() can be called to
initialize a new digest operation.
EVP_MD_CTX_copy() 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_MD_size() and EVP_MD_CTX_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_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
respectively. 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
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signature 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
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 VALUES
EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal()
do not return values.
EVP_MD_CTX_copy() 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.
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>
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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_DigestInit(&mdctx, md);
EVP_DigestUpdate(&mdctx, mess1, strlen(mess1));
EVP_DigestUpdate(&mdctx, mess2, strlen(mess2));
EVP_DigestFinal(&mdctx, md_value, &md_len);
printf("Digest is: ");
for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);
printf("\n");
}
BUGS
Several of the functions do not return values: maybe they
should. Although the internal digest operations will never
fail some future hardware based operations might.
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
identical digests.
The size of an EVP_MD_CTX structure is determined at compile
time: this results in code that must be recompiled if the
size of EVP_MD_CTX increases.
SEE ALSO
evp(3), hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3),
dgst(1)
HISTORY
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EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal()
are available in all versions of SSLeay and OpenSSL.
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