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 routines

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)

        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
       message 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
       digest 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 sev-
       eral 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_Diges-
       tUpdate() 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 bytes. out must be initialized before call-
       ing this function.

       EVP_DigestInit() behaves in the same way as EVP_Diges-
       tInit_ex() except the passed context ctx does not have
       to be initialized, and it always uses the default digest
       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 initial-
       ized.

       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 correspond-
       ing to the passed EVP_MD_CTX.

       EVP_MD_pkey_type() returns the NID of the public key
       signing algorithm associated with this digest. For exam-
       ple 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 algo-
       rithms 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 signature algorithm.

       EVP_md_null() is a "null" message digest that does noth-
       ing: 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 ini-
       tialized using, for example, OpenSSL_add_all_digests()
       for these functions to work.

RETURN VALUES
       EVP_DigestInit_ex(), EVP_DigestUpdate() and EVP_Digest-
       Final_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 inter-
       faces. 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_Diges-
       tInit_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 main-
       tain 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.

       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 identical digests.

SEE ALSO
       evp(3), hmac(3), md2(3), md5(3), mdc2(3), ripemd(3),
       sha(3), dgst(1)

HISTORY
       EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFi-
       nal() 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.



0.9.7c                     2002-07-18         EVP_DigestInit(3)
