BIO_get_md_ctx.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest BIO filter .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 2 \& #include <openssl/bio.h> \& #include <openssl/evp.h> \& \& const 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); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter \&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper for the digest routines \fBEVP_DigestInit()\fR, \fBEVP_DigestUpdate()\fR and \fBEVP_DigestFinal()\fR. .PP Any data written or read through a digest \s-1BIO\s0 using \fBBIO_read_ex()\fR and \&\fBBIO_write_ex()\fR is digested. .PP \&\fBBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the digest calculation and returns the digest value. \fBBIO_puts()\fR is not supported. .PP \&\fBBIO_reset()\fR reinitialises a digest \s-1BIO.\s0 .PP \&\fBBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this must be called to initialize a digest \s-1BIO\s0 before any data is passed through it. It is a \fBBIO_ctrl()\fR macro. .PP \&\fBBIO_get_md()\fR places the a pointer to the digest BIOs digest method in \fBmdp\fR, it is a \fBBIO_ctrl()\fR macro. .PP \&\fBBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR. .SH "NOTES" .IX Header "NOTES" The context returned by \fBBIO_get_md_ctx()\fR can be used in calls to \fBEVP_DigestFinal()\fR and also the signature routines \fBEVP_SignFinal()\fR and \fBEVP_VerifyFinal()\fR. .PP The context returned by \fBBIO_get_md_ctx()\fR is an internal context structure. Changes made to this context will affect the digest \&\s-1BIO\s0 itself and the context pointer will become invalid when the digest \&\s-1BIO\s0 is freed. .PP After the digest has been retrieved from a digest \s-1BIO\s0 it must be reinitialized by calling \fBBIO_reset()\fR, or \fBBIO_set_md()\fR before any more data is passed through it. .PP If an application needs to call \fBBIO_gets()\fR or \fBBIO_puts()\fR through a chain containing digest BIOs then this can be done by prepending a buffering \s-1BIO.\s0 .PP Calling \fBBIO_get_md_ctx()\fR will return the context and initialize the \s-1BIO\s0 state. This allows applications to initialize the context externally if the standard calls such as \fBBIO_set_md()\fR are not sufficiently flexible. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBBIO_f_md()\fR returns the digest \s-1BIO\s0 method. .PP \&\fBBIO_set_md()\fR, \fBBIO_get_md()\fR and \fBBIO_md_ctx()\fR return 1 for success and 0 for failure. .SH "EXAMPLES" .IX Header "EXAMPLES" The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0 digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error checking has been omitted for clarity. .PP .Vb 2 \& 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)); .Ve .PP The next example digests data by reading through a chain instead: .PP .Vb 3 \& 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); .Ve .PP This next example retrieves the message digests from a \s-1BIO\s0 chain and outputs them. This could be used with the examples above. .PP .Vb 4 \& 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("\en"); \& mdtmp = BIO_next(mdtmp); \& } while (mdtmp); \& \& BIO_free_all(bio); .Ve .SH "BUGS" .IX Header "BUGS" The lack of support for \fBBIO_puts()\fR and the non standard behaviour of \&\fBBIO_gets()\fR could be regarded as anomalous. It could be argued that \fBBIO_gets()\fR and \fBBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest the data passed through and that digests should be retrieved using a separate \fBBIO_ctrl()\fR call. .SH "HISTORY" .IX Header "HISTORY" Before OpenSSL 1.0.0., the call to \fBBIO_get_md_ctx()\fR would only work if the \&\s-1BIO\s0 was initialized first. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2000\-2016 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.
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