Updated: 2021/Apr/14


EVP_DigestInit(3)                   OpenSSL                  EVP_DigestInit(3)



NAME
       EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy,
       EVP_MD_CTX_copy_ex, EVP_MD_CTX_ctrl, EVP_MD_CTX_set_flags,
       EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags, EVP_Digest,
       EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,
       EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal, EVP_MD_type,
       EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_flags,
       EVP_MD_CTX_md, EVP_MD_CTX_type, EVP_MD_CTX_size, EVP_MD_CTX_block_size,
       EVP_MD_CTX_md_data, EVP_MD_CTX_update_fn, EVP_MD_CTX_set_update_fn,
       EVP_md_null, EVP_get_digestbyname, EVP_get_digestbynid,
       EVP_get_digestbyobj, EVP_MD_CTX_pkey_ctx, EVP_MD_CTX_set_pkey_ctx - EVP
       digest routines

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        EVP_MD_CTX *EVP_MD_CTX_new(void);
        int EVP_MD_CTX_reset(EVP_MD_CTX *ctx);
        void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
        void EVP_MD_CTX_ctrl(EVP_MD_CTX *ctx, int cmd, int p1, void* p2);
        void EVP_MD_CTX_set_flags(EVP_MD_CTX *ctx, int flags);
        void EVP_MD_CTX_clear_flags(EVP_MD_CTX *ctx, int flags);
        int EVP_MD_CTX_test_flags(const EVP_MD_CTX *ctx, int flags);

        int EVP_Digest(const void *data, size_t count, unsigned char *md,
                       unsigned int *size, const EVP_MD *type, ENGINE *impl);
        int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
        int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
        int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);
        int EVP_DigestFinalXOF(EVP_MD_CTX *ctx, unsigned char *md, size_t len);

        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);

        int EVP_MD_type(const EVP_MD *md);
        int EVP_MD_pkey_type(const EVP_MD *md);
        int EVP_MD_size(const EVP_MD *md);
        int EVP_MD_block_size(const EVP_MD *md);
        unsigned long EVP_MD_flags(const EVP_MD *md);

        const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
        int EVP_MD_CTX_size(const EVP_MD_CTX *ctx);
        int EVP_MD_CTX_block_size(const EVP_MD_CTX *ctx);
        int EVP_MD_CTX_type(const EVP_MD_CTX *ctx);
        void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);
        int (*EVP_MD_CTX_update_fn(EVP_MD_CTX *ctx))(EVP_MD_CTX *ctx,
                                                     const void *data, size_t count);
        void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,
                                      int (*update)(EVP_MD_CTX *ctx,
                                                    const void *data, size_t count));

        const EVP_MD *EVP_md_null(void);

        const EVP_MD *EVP_get_digestbyname(const char *name);
        const EVP_MD *EVP_get_digestbynid(int type);
        const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *o);

        EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx);
        void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);

DESCRIPTION
       The EVP digest routines are a high-level interface to message digests,
       and should be used instead of the cipher-specific functions.

       EVP_MD_CTX_new()
           Allocates and returns a digest context.

       EVP_MD_CTX_reset()
           Resets the digest context ctx.  This can be used to reuse an
           already existing context.

       EVP_MD_CTX_free()
           Cleans up digest context ctx and frees up the space allocated to
           it.

       EVP_MD_CTX_ctrl()
           Performs digest-specific control actions on context ctx. The
           control command is indicated in cmd and any additional arguments in
           p1 and p2.  EVP_MD_CTX_ctrl() must be called after
           EVP_DigestInit_ex(). Other restrictions may apply depending on the
           control type and digest implementation.  See "CONTROLS" below for
           more information.

       EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(),
       EVP_MD_CTX_test_flags()
           Sets, clears and tests ctx flags.  See "FLAGS" below for more
           information.

       EVP_Digest()
           A wrapper around the Digest Init_ex, Update and Final_ex functions.
           Hashes count bytes of data at data using a digest type from ENGINE
           impl. The digest value is placed in md and its length is written at
           size if the pointer is not NULL. At most EVP_MAX_MD_SIZE bytes will
           be written.  If impl is NULL the default implementation of digest
           type is used.

       EVP_DigestInit_ex()
           Sets up digest context ctx to use a digest type from ENGINE impl.
           type will typically be supplied by a function such 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 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_DigestUpdate() can
           be made, but EVP_DigestInit_ex() can be called to initialize a new
           digest operation.

       EVP_DigestFinalXOF()
           Interfaces to extendable-output functions, XOFs, such as SHAKE128
           and SHAKE256. It retrieves the digest value from ctx and places it
           in len-sized <B>md.  After calling this function no additional
           calls to EVP_DigestUpdate() can be made, but EVP_DigestInit_ex()
           can be called to initialize a new operation.

       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.

       EVP_DigestInit()
           Behaves in the same way as EVP_DigestInit_ex() except it always
           uses the default digest implementation and calls
           EVP_MD_CTX_reset().

       EVP_DigestFinal()
           Similar to EVP_DigestFinal_ex() except the digest context ctx is
           automatically cleaned up.

       EVP_MD_CTX_copy()
           Similar to EVP_MD_CTX_copy_ex() except the destination out does not
           have to be initialized.

       EVP_MD_size(), 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(), 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(), 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_data()
           Return the digest method private data for the passed EVP_MD_CTX.
           The space is allocated by OpenSSL and has the size originally set
           with EVP_MD_meth_set_app_datasize().

       EVP_MD_CTX_md()
           Returns the EVP_MD structure corresponding to the passed
           EVP_MD_CTX.

       EVP_MD_CTX_set_update_fn()
           Sets the update function for ctx to update.  This is the function
           that is called by EVP_DigestUpdate. If not set, the update function
           from the EVP_MD type specified at initialization is used.

       EVP_MD_CTX_update_fn()
           Returns the update function for ctx.

       EVP_MD_flags()
           Returns the md flags. Note that these are different from the
           EVP_MD_CTX ones. See EVP_MD_meth_set_flags(3) for more information.

       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. Since digests and signature
           algorithms are no longer linked this function is only retained for
           compatibility reasons.

       EVP_md_null()
           A "null" message digest that does nothing: i.e. the hash it returns
           is of zero length.

       EVP_get_digestbyname(), EVP_get_digestbynid(), EVP_get_digestbyobj()
           Returns an EVP_MD structure when passed a digest name, a digest NID
           or an ASN1_OBJECT structure respectively.

       EVP_MD_CTX_pkey_ctx()
           Returns the EVP_PKEY_CTX assigned to ctx. The returned pointer
           should not be freed by the caller.

       EVP_MD_CTX_set_pkey_ctx()
           Assigns an EVP_PKEY_CTX to EVP_MD_CTX. This is usually used to
           provide a customized EVP_PKEY_CTX to EVP_DigestSignInit(3) or
           EVP_DigestVerifyInit(3). The pctx passed to this function should be
           freed by the caller. A NULL pctx pointer is also allowed to clear
           the EVP_PKEY_CTX assigned to ctx. In such case, freeing the cleared
           EVP_PKEY_CTX or not depends on how the EVP_PKEY_CTX is created.

CONTROLS
       EVP_MD_CTX_ctrl() can be used to send the following standard controls:

       EVP_MD_CTRL_MICALG
           Gets the digest Message Integrity Check algorithm string. This is
           used when creating S/MIME multipart/signed messages, as specified
           in RFC 3851. The string value is written to p2.

       EVP_MD_CTRL_XOF_LEN
           This control sets the digest length for extendable output functions
           to p1.  Sending this control directly should not be necessary, the
           use of "EVP_DigestFinalXOF()" is preferred.  Currently used by
           SHAKE.

FLAGS
       EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags() and
       EVP_MD_CTX_test_flags() can be used the manipulate and test these
       EVP_MD_CTX flags:

       EVP_MD_CTX_FLAG_ONESHOT
           This flag instructs the digest to optimize for one update only, if
           possible.

       EVP_MD_CTX_FLAG_NO_INIT
           This flag instructs EVP_DigestInit() and similar not to initialise
           the implementation specific data.

       EVP_MD_CTX_FLAG_FINALISE
           Some functions such as EVP_DigestSign only finalise copies of
           internal contexts so additional data can be included after the
           finalisation call.  This is inefficient if this functionality is
           not required, and can be disabled with this flag.

RETURN VALUES
       EVP_DigestInit_ex(), EVP_DigestUpdate(), EVP_DigestFinal_ex()
           Returns 1 for success and 0 for failure.

       EVP_MD_CTX_ctrl()
           Returns 1 if successful or 0 for failure.

       EVP_MD_CTX_copy_ex()
           Returns 1 if successful or 0 for failure.

       EVP_MD_type(), EVP_MD_pkey_type()
           Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef
           if none exists.

       EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(),
       EVP_MD_CTX_block_size()
           Returns the digest or block size in bytes.

       EVP_md_null()
           Returns a pointer to the EVP_MD structure of the "null" message
           digest.

       EVP_get_digestbyname(), EVP_get_digestbynid(), EVP_get_digestbyobj()
           Returns either an EVP_MD structure or NULL if an error occurs.

       EVP_MD_CTX_set_pkey_ctx()
           This function has no return value.

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.

       New applications should use the SHA-2 (such as EVP_sha256(3)) or the
       SHA-3 digest algorithms (such as EVP_sha3_512(3)). 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.

       If digest contexts are not cleaned up after use, memory leaks will
       occur.

       EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_type(),
       EVP_get_digestbynid() and EVP_get_digestbyobj() are defined as macros.

       EVP_MD_CTX_ctrl() sends commands to message digests for additional
       configuration or control.

EXAMPLES
       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 <string.h>
        #include <openssl/evp.h>

        int 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];
            unsigned int md_len, i;

            if (argv[1] == NULL) {
                printf("Usage: mdtest digestname\n");
                exit(1);
            }

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

            mdctx = EVP_MD_CTX_new();
            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_free(mdctx);

            printf("Digest is: ");
            for (i = 0; i < md_len; i++)
                printf("%02x", md_value[i]);
            printf("\n");

            exit(0);
        }

SEE ALSO
       EVP_MD_meth_new(3), dgst(1), evp(7)

       The full list of digest algorithms are provided below.

       EVP_blake2b512(3), EVP_md2(3), EVP_md4(3), EVP_md5(3), EVP_mdc2(3),
       EVP_ripemd160(3), EVP_sha1(3), EVP_sha224(3), EVP_sha3_224(3),
       EVP_sm3(3), EVP_whirlpool(3)

HISTORY
       The EVP_MD_CTX_create() and EVP_MD_CTX_destroy() functions were renamed
       to EVP_MD_CTX_new() and EVP_MD_CTX_free() in OpenSSL 1.1.0,
       respectively.

       The link between digests and signing algorithms was fixed in OpenSSL
       1.0 and later, so now EVP_sha1() can be used with RSA and DSA.

       The EVP_dss1() function was removed in OpenSSL 1.1.0.

       The EVP_MD_CTX_set_pkey_ctx() function was added in 1.1.1.

COPYRIGHT
       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



1.1.1i                            2020-12-10                 EVP_DigestInit(3)