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145 lines
4.4 KiB
Plaintext
145 lines
4.4 KiB
Plaintext
=pod
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=head1 NAME
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BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO filter
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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#include <openssl/evp.h>
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BIO_METHOD * BIO_f_md(void);
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int BIO_set_md(BIO *b,EVP_MD *md);
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int BIO_get_md(BIO *b,EVP_MD **mdp);
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int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
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=head1 DESCRIPTION
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BIO_f_md() returns the message digest BIO method. This is a filter
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BIO that digests any data passed through it, it is a BIO wrapper
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for the digest routines EVP_DigestInit(), EVP_DigestUpdate()
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and EVP_DigestFinal().
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Any data written or read through a digest BIO using BIO_read() and
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BIO_write() is digested.
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BIO_gets(), if its B<size> parameter is large enough finishes the
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digest calculation and returns the digest value. BIO_puts() is
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not supported.
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BIO_reset() reinitialises a digest BIO.
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BIO_set_md() sets the message digest of BIO B<b> to B<md>: this
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must be called to initialize a digest BIO before any data is
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passed through it. It is a BIO_ctrl() macro.
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BIO_get_md() places the a pointer to the digest BIOs digest method
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in B<mdp>, it is a BIO_ctrl() macro.
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BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>.
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=head1 NOTES
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The context returned by BIO_get_md_ctx() can be used in calls
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to EVP_DigestFinal() and also the signature routines EVP_SignFinal()
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and EVP_VerifyFinal().
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The context returned by BIO_get_md_ctx() is an internal context
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structure. Changes made to this context will affect the digest
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BIO itself and the context pointer will become invalid when the digest
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BIO is freed.
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After the digest has been retrieved from a digest BIO it must be
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reinitialized by calling BIO_reset(), or BIO_set_md() before any more
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data is passed through it.
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If an application needs to call BIO_gets() or BIO_puts() through
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a chain containing digest BIOs then this can be done by prepending
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a buffering BIO.
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Before OpenSSL 1.0.0 the call to BIO_get_md_ctx() would only work if the BIO
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had been initialized for example by calling BIO_set_md() ). In OpenSSL
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1.0.0 and later the context is always returned and the BIO is state is set
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to initialized. This allows applications to initialize the context externally
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if the standard calls such as BIO_set_md() are not sufficiently flexible.
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=head1 RETURN VALUES
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BIO_f_md() returns the digest BIO method.
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BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and
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0 for failure.
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=head1 EXAMPLES
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The following example creates a BIO chain containing an SHA1 and MD5
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digest BIO and passes the string "Hello World" through it. Error
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checking has been omitted for clarity.
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BIO *bio, *mdtmp;
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char message[] = "Hello World";
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bio = BIO_new(BIO_s_null());
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mdtmp = BIO_new(BIO_f_md());
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BIO_set_md(mdtmp, EVP_sha1());
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/* For BIO_push() we want to append the sink BIO and keep a note of
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* the start of the chain.
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*/
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bio = BIO_push(mdtmp, bio);
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mdtmp = BIO_new(BIO_f_md());
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BIO_set_md(mdtmp, EVP_md5());
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bio = BIO_push(mdtmp, bio);
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/* Note: mdtmp can now be discarded */
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BIO_write(bio, message, strlen(message));
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The next example digests data by reading through a chain instead:
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BIO *bio, *mdtmp;
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char buf[1024];
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int rdlen;
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bio = BIO_new_file(file, "rb");
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mdtmp = BIO_new(BIO_f_md());
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BIO_set_md(mdtmp, EVP_sha1());
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bio = BIO_push(mdtmp, bio);
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mdtmp = BIO_new(BIO_f_md());
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BIO_set_md(mdtmp, EVP_md5());
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bio = BIO_push(mdtmp, bio);
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do {
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rdlen = BIO_read(bio, buf, sizeof(buf));
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/* Might want to do something with the data here */
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} while(rdlen > 0);
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This next example retrieves the message digests from a BIO chain and
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outputs them. This could be used with the examples above.
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BIO *mdtmp;
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unsigned char mdbuf[EVP_MAX_MD_SIZE];
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int mdlen;
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int i;
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mdtmp = bio; /* Assume bio has previously been set up */
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do {
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EVP_MD *md;
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mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
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if(!mdtmp) break;
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BIO_get_md(mdtmp, &md);
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printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
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mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
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for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]);
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printf("\n");
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mdtmp = BIO_next(mdtmp);
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} while(mdtmp);
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BIO_free_all(bio);
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=head1 BUGS
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The lack of support for BIO_puts() and the non standard behaviour of
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BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets()
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and BIO_puts() should be passed to the next BIO in the chain and digest
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the data passed through and that digests should be retrieved using a
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separate BIO_ctrl() call.
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=head1 SEE ALSO
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TBA
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