BIO_f_md(3)                         OpenSSL                        BIO_f_md(3)



NNAAMMEE
       BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO
       filter

SSYYNNOOPPSSIISS
        #include <openssl/bio.h>
        #include <openssl/evp.h>

        BIO_METHOD *   BIO_f_md(void);
        int BIO_set_md(BIO *b,EVP_MD *md);
        int BIO_get_md(BIO *b,EVP_MD **mdp);
        int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);

DDEESSCCRRIIPPTTIIOONN
       _B_I_O___f___m_d_(_) returns the message digest BIO method. This is a filter BIO
       that digests any data passed through it, it is a BIO wrapper for the
       digest routines _E_V_P___D_i_g_e_s_t_I_n_i_t_(_), _E_V_P___D_i_g_e_s_t_U_p_d_a_t_e_(_) and _E_V_P___D_i_g_e_s_t_F_i_-
       _n_a_l_(_).

       Any data written or read through a digest BIO using _B_I_O___r_e_a_d_(_) and
       _B_I_O___w_r_i_t_e_(_) is digested.

       _B_I_O___g_e_t_s_(_), if its ssiizzee parameter is large enough finishes the digest
       calculation and returns the digest value. _B_I_O___p_u_t_s_(_) is not supported.

       _B_I_O___r_e_s_e_t_(_) reinitialises a digest BIO.

       _B_I_O___s_e_t___m_d_(_) sets the message digest of BIO bb to mmdd: this must be
       called to initialize a digest BIO before any data is passed through it.
       It is a _B_I_O___c_t_r_l_(_) macro.

       _B_I_O___g_e_t___m_d_(_) places the a pointer to the digest BIOs digest method in
       mmddpp, it is a _B_I_O___c_t_r_l_(_) macro.

       _B_I_O___g_e_t___m_d___c_t_x_(_) returns the digest BIOs context into mmddccpp.

NNOOTTEESS
       The context returned by _B_I_O___g_e_t___m_d___c_t_x_(_) can be used in calls to
       _E_V_P___D_i_g_e_s_t_F_i_n_a_l_(_) and also the signature routines _E_V_P___S_i_g_n_F_i_n_a_l_(_) and
       _E_V_P___V_e_r_i_f_y_F_i_n_a_l_(_).

       The context returned by _B_I_O___g_e_t___m_d___c_t_x_(_) is an internal context struc-
       ture. Changes made to this context will affect the digest BIO itself
       and the context pointer will become invalid when the digest BIO is
       freed.

       After the digest has been retrieved from a digest BIO it must be reini-
       tialized by calling _B_I_O___r_e_s_e_t_(_), or _B_I_O___s_e_t___m_d_(_) before any more data
       is passed through it.

       If an application needs to call _B_I_O___g_e_t_s_(_) or _B_I_O___p_u_t_s_(_) through a
       chain containing digest BIOs then this can be done by prepending a
       buffering BIO.

       Before OpenSSL 1.0.0 the call to _B_I_O___g_e_t___m_d___c_t_x_(_) would only work if
       the BIO had been initialized for example by calling _B_I_O___s_e_t___m_d_(_) ). In
       OpenSSL 1.0.0 and later the context is always returned and the BIO is
       state is set to initialized. This allows applications to initialize the
       context externally if the standard calls such as _B_I_O___s_e_t___m_d_(_) are not
       sufficiently flexible.

RREETTUURRNN VVAALLUUEESS
       _B_I_O___f___m_d_(_) returns the digest BIO method.

       _B_I_O___s_e_t___m_d_(_), _B_I_O___g_e_t___m_d_(_) and _B_I_O___m_d___c_t_x_(_) return 1 for success and 0
       for failure.

EEXXAAMMPPLLEESS
       The following example creates a BIO chain containing an SHA1 and MD5
       digest BIO and passes the string "Hello World" through it. Error check-
       ing has been omitted for clarity.

        BIO *bio, *mdtmp;
        char message[] = "Hello World";
        bio = BIO_new(BIO_s_null());
        mdtmp = BIO_new(BIO_f_md());
        BIO_set_md(mdtmp, EVP_sha1());
        /* For BIO_push() we want to append the sink BIO and keep a note of
         * the start of the chain.
         */
        bio = BIO_push(mdtmp, bio);
        mdtmp = BIO_new(BIO_f_md());
        BIO_set_md(mdtmp, EVP_md5());
        bio = BIO_push(mdtmp, bio);
        /* Note: mdtmp can now be discarded */
        BIO_write(bio, message, strlen(message));

       The next example digests data by reading through a chain instead:

        BIO *bio, *mdtmp;
        char buf[1024];
        int rdlen;
        bio = BIO_new_file(file, "rb");
        mdtmp = BIO_new(BIO_f_md());
        BIO_set_md(mdtmp, EVP_sha1());
        bio = BIO_push(mdtmp, bio);
        mdtmp = BIO_new(BIO_f_md());
        BIO_set_md(mdtmp, EVP_md5());
        bio = BIO_push(mdtmp, bio);
        do {
               rdlen = BIO_read(bio, buf, sizeof(buf));
               /* Might want to do something with the data here */
        } while(rdlen > 0);

       This next example retrieves the message digests from a BIO chain and
       outputs them. This could be used with the examples above.

        BIO *mdtmp;
        unsigned char mdbuf[EVP_MAX_MD_SIZE];
        int mdlen;
        int i;
        mdtmp = bio;   /* Assume bio has previously been set up */
        do {
               EVP_MD *md;
               mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
               if(!mdtmp) break;
               BIO_get_md(mdtmp, &md);
               printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
               mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
               for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
               printf("\n");
               mdtmp = BIO_next(mdtmp);
        } while(mdtmp);

        BIO_free_all(bio);

BBUUGGSS
       The lack of support for _B_I_O___p_u_t_s_(_) and the non standard behaviour of
       _B_I_O___g_e_t_s_(_) could be regarded as anomalous. It could be argued that
       _B_I_O___g_e_t_s_(_) and _B_I_O___p_u_t_s_(_) should be passed to the next BIO in the chain
       and digest the data passed through and that digests should be retrieved
       using a separate _B_I_O___c_t_r_l_(_) call.

SSEEEE AALLSSOO
       TBA



1.0.1u                            2016-09-22                       BIO_f_md(3)