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BIO(3)		      DragonFly Library Functions Manual		BIO(3)

NAME

BIO -- I/O abstraction

SYNOPSIS

#include <openssl/bio.h>

DESCRIPTION

A BIO is an I/O abstraction, it hides many of the underlying I/O details from an application. If an application uses a BIO for its I/O, it can transparently handle SSL connections, unencrypted network connections and file I/O. There are two types of BIO, a source/sink BIO and a filter BIO. As its name implies, a source/sink BIO is a source and/or sink of data, examples include a socket BIO and a file BIO. A filter BIO takes data from one BIO and passes it through to another, or to the application. The data may be left unmodified (for example a mes- sage digest BIO) or translated (for example an encryption BIO). The effect of a filter BIO may change according to the I/O operation it is performing: for example an encryption BIO will encrypt data if it is being written to and decrypt data if it is being read from. BIOs can be joined together to form a chain (a single BIO is a chain with one component). A chain normally consist of one source/sink BIO and one or more filter BIOs. Data read from or written to the first BIO then traverses the chain to the end (normally a source/sink BIO).

SEE ALSO

BIO_ctrl(3), BIO_f_base64(3), BIO_f_buffer(3), BIO_f_cipher(3), BIO_f_md(3), BIO_f_null(3), BIO_f_ssl(3), BIO_find_type(3), BIO_new(3), BIO_new_bio_pair(3), BIO_push(3), BIO_read(3), BIO_s_accept(3), BIO_s_bio(3), BIO_s_connect(3), BIO_s_fd(3), BIO_s_file(3), BIO_s_mem(3), BIO_s_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_should_retry(3) DragonFly 4.7 July 17, 2014 DragonFly 4.7 BIO_f_md(3) OpenSSL BIO_f_md(3)

NAME

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

SYNOPSIS

#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);

DESCRIPTION

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 EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal(). Any data written or read through a digest BIO using BIO_read() and BIO_write() is digested. BIO_gets(), if its size parameter is large enough finishes the digest calculation and returns the digest value. BIO_puts() is not supported. BIO_reset() reinitialises a digest BIO. BIO_set_md() sets the message digest of BIO b to md: this must be called to initialize a digest BIO before any data is passed through it. It is a BIO_ctrl() macro. BIO_get_md() places the a pointer to the digest BIOs digest method in mdp, it is a BIO_ctrl() macro. BIO_get_md_ctx() returns the digest BIOs context into mdcp.

NOTES

The context returned by BIO_get_md_ctx() can be used in calls to EVP_DigestFinal() and also the signature routines EVP_SignFinal() and EVP_VerifyFinal(). The context returned by 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. After the digest has been retrieved from a digest BIO it must be reinitialized by calling BIO_reset(), or BIO_set_md() before any more data is passed through it. If an application needs to call BIO_gets() or BIO_puts() through a chain containing digest BIOs then this can be done by prepending a buffering BIO. Before OpenSSL 1.0.0 the call to BIO_get_md_ctx() would only work if the BIO had been initialized for example by calling BIO_set_md() ). 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 BIO_set_md() are not sufficiently flexible.

RETURN VALUES

BIO_f_md() returns the digest BIO method. BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and 0 for failure.

EXAMPLES

The following example creates a BIO chain containing an SHA1 and MD5 digest BIO and passes the string "Hello World" through it. Error checking 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);

BUGS

The lack of support for BIO_puts() and the non standard behaviour of BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets() and BIO_puts() 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 BIO_ctrl() call.

SEE ALSO

TBA 1.0.2h 2016-05-03 BIO_f_md(3)

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