*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->NetBSD man pages -> EVP_DigestInit (3)              



NAME    [Toc]    [Back]

       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

LIBRARY    [Toc]    [Back]

       libcrypto, -lcrypto

SYNOPSIS    [Toc]    [Back]

        #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    [Toc]    [Back]

       The EVP digest routines are a high level interface to message

       EVP_DigestInit() initializes a digest context ctx to use a
       digest type: this will typically be supplied by a function
       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_DigestUp-
       date() 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

       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
       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    [Toc]    [Back]

       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

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       This example digests the data "Test Message\n" and "Hello
       World\n", using the digest name passed on the command

        #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;


        if(!argv[1]) {
               printf("Usage: mdtest digestname\n");

        md = EVP_get_digestbyname(argv[1]);

        if(!md) {
               printf("Unknown message digest %s\n", argv[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]);

BUGS    [Toc]    [Back]

       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    [Toc]    [Back]

       openssl_evp(3), openssl_hmac(3), md2(3), openssl_md5(3),
       openssl_mdc2(3), openssl_ripemd(3), openssl_sha(3),

HISTORY    [Toc]    [Back]

       EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal()
       are available in all versions of SSLeay and OpenSSL.

2002-07-31                    0.9.6g            EVP_DigestInit(3)
[ Back ]
 Similar pages
Name OS Title
md5 OpenBSD message digest routines
MD5Transform OpenBSD message digest routines
MD5Init OpenBSD message digest routines
MD5Transform FreeBSD message digest routines
MD5Init FreeBSD message digest routines
MD5 FreeBSD message digest routines
BIO_get_md_ctx Tru64 Message digest BIO filter
BIO_f_md NetBSD message digest BIO filter
BIO_get_md Tru64 Message digest BIO filter
BIO_set_md Tru64 Message digest BIO filter
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service