283 lines
8.6 KiB
Groff
283 lines
8.6 KiB
Groff
.\" $NetBSD: BIO_f_md.3,v 1.5 2002/07/31 01:45:22 itojun Exp $
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.\" ======================================================================
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.\"
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.IX Title "BIO_f_md 3"
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.TH BIO_f_md 3 "0.9.6e" "2001-04-12" "OpenSSL"
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.UC
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.SH "NAME"
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BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest \s-1BIO\s0 filter
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 2
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\& #include <openssl/bio.h>
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\& #include <openssl/evp.h>
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.Ve
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.Vb 4
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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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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
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\&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
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for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
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and \fIEVP_DigestFinal()\fR.
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.PP
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Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
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\&\fIBIO_write()\fR is digested.
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.PP
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\&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
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digest calculation and returns the digest value. \fIBIO_puts()\fR is
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not supported.
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.PP
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\&\fIBIO_reset()\fR reinitializes a digest \s-1BIO\s0.
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.PP
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\&\fIBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this
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must be called to initialize a digest \s-1BIO\s0 before any data is
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passed through it. It is a \fIBIO_ctrl()\fR macro.
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.PP
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\&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
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in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
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.PP
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\&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
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.SH "NOTES"
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.IX Header "NOTES"
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The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
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to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
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and \fIEVP_VerifyFinal()\fR.
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.PP
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The context returned by \fIBIO_get_md_ctx()\fR is an internal context
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structure. Changes made to this context will affect the digest
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\&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
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\&\s-1BIO\s0 is freed.
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.PP
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After the digest has been retrieved from a digest \s-1BIO\s0 it must be
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reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
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data is passed through it.
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.PP
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If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
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a chain containing digest BIOs then this can be done by prepending
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a buffering \s-1BIO\s0.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
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.PP
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\&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
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0 for failure.
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
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digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
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checking has been omitted for clarity.
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.PP
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.Vb 14
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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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.Ve
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The next example digests data by reading through a chain instead:
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.PP
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.Vb 14
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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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.Ve
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This next example retrieves the message digests from a \s-1BIO\s0 chain and
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outputs them. This could be used with the examples above.
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.PP
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.Vb 16
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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("\en");
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\& mdtmp = BIO_next(mdtmp);
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\& } while(mdtmp);
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.Ve
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.Vb 1
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\& BIO_free_all(bio);
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.Ve
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.SH "BUGS"
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.IX Header "BUGS"
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The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
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\&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
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and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 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 \fIBIO_ctrl()\fR call.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\s-1TBA\s0
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