.\" $OpenBSD: BIO_f_md.3,v 1.7 2017/01/07 08:46:13 jmc Exp $ .\" OpenSSL a528d4f0 Oct 27 13:40:11 2015 -0400 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2000, 2006, 2009, 2016 The OpenSSL Project. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: January 7 2017 $ .Dt BIO_F_MD 3 .Os .Sh NAME .Nm BIO_f_md , .Nm BIO_set_md , .Nm BIO_get_md , .Nm BIO_get_md_ctx .Nd message digest BIO filter .Sh SYNOPSIS .In openssl/bio.h .In openssl/evp.h .Ft BIO_METHOD * .Fo BIO_f_md .Fa void .Fc .Ft int .Fo BIO_set_md .Fa "BIO *b" .Fa "EVP_MD *md" .Fc .Ft int .Fo BIO_get_md .Fa "BIO *b" .Fa "EVP_MD **mdp" .Fc .Ft int .Fo BIO_get_md_ctx .Fa "BIO *b" .Fa "EVP_MD_CTX **mdcp" .Fc .Sh DESCRIPTION .Fn BIO_f_md 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 .Xr EVP_DigestInit 3 , .Xr EVP_DigestUpdate 3 , and .Xr EVP_DigestFinal 3 . .Pp Any data written or read through a digest BIO using .Xr BIO_read 3 and .Xr BIO_write 3 is digested. .Pp .Xr BIO_gets 3 , if its .Sy size parameter is large enough, finishes the digest calculation and returns the digest value. .Xr BIO_puts 3 is not supported. .Pp .Xr BIO_reset 3 reinitialises a digest BIO. .Pp .Fn BIO_set_md sets the message digest of BIO .Fa b to .Fa md : this must be called to initialize a digest BIO before any data is passed through it. It is a .Xr BIO_ctrl 3 macro. .Pp .Fn BIO_get_md places a pointer to the digest BIOs digest method in .Fa mdp . It is a .Xr BIO_ctrl 3 macro. .Pp .Fn BIO_get_md_ctx returns the digest BIOs context in .Fa mdcp . .Pp The context returned by .Fn BIO_get_md_ctx can be used in calls to .Xr EVP_DigestFinal 3 and also in the signature routines .Xr EVP_SignFinal 3 and .Xr EVP_VerifyFinal 3 . .Pp The context returned by .Fn BIO_get_md_ctx is an internal context structure. Changes made to this context will affect the digest BIO itself, and the context pointer will become invalid when the digest BIO is freed. .Pp After the digest has been retrieved from a digest BIO, it must be reinitialized by calling .Xr BIO_reset 3 or .Fn BIO_set_md before any more data is passed through it. .Pp If an application needs to call .Xr BIO_gets 3 or .Xr BIO_puts 3 through a chain containing digest BIOs, then this can be done by prepending a buffering BIO. .Pp Calling .Fn BIO_get_md_ctx will return the context and initialize the .Vt BIO state. This allows applications to initialize the context externally if the standard calls such as .Fn BIO_set_md are not sufficiently flexible. .Sh RETURN VALUES .Fn BIO_f_md returns the digest BIO method. .Pp .Fn BIO_set_md , .Fn BIO_get_md , and .Fn BIO_get_md_ctx return 1 for success and 0 for failure. .Sh EXAMPLES The following example creates a BIO chain containing a SHA-1 and MD5 digest BIO and passes the string "Hello World" through it. Error checking has been omitted for clarity. .Bd -literal -offset 2n BIO *bio, *mdtmp; const 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)); .Ed .Pp The next example digests data by reading through a chain instead: .Bd -literal -offset 2n 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); .Ed .Pp This next example retrieves the message digests from a BIO chain and outputs them. This could be used with the examples above. .Bd -literal -offset 2n 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); .Ed .Sh SEE ALSO .Xr BIO_new 3 .Sh HISTORY Before OpenSSL 1.0.0, the call to .Fn BIO_get_md_ctx would only work if the .Vt BIO had been initialized, for example by calling .Fn BIO_set_md . .Sh BUGS The lack of support for .Xr BIO_puts 3 and the non-standard behaviour of .Xr BIO_gets 3 could be regarded as anomalous. It could be argued that .Xr BIO_gets 3 and .Xr BIO_puts 3 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 .Xr BIO_ctrl 3 call.