BIO_f_md(3)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(
BIO *b,
EVP_MD_CTX **mdcp );
DESCRIPTIONBIO_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
EVP_DigestInit(), EVP_DigestUpdate(), and EVP_DigestFinal() digest
functions.
Any data written or read through a digest BIO using BIO_read() and
BIO_write() is digested.
The BIO_gets() function, if its size parameter is large enough, fin‐
ishes the digest calculation and returns the digest value. The
BIO_puts() function is not supported.
The BIO_reset() function reinitializes a digest BIO.
The BIO_set_md() function 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.
The BIO_get_md() function places the a pointer to the digest BIOs
digest method in mdp. It is a BIO_ctrl() macro.
The BIO_get_md_ctx() function returns the digest BIOs context into
mdcp.
NOTES
The context returned by the BIO_get_md_ctx() function can be used in
calls to the EVP_DigestFinal(), EVP_SignFinal(), and EVP_VerifyFinal()
functions.
The context returned by the BIO_get_md_ctx() function 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 reini‐
tialized 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.
RESTRICTIONS
The lack of support for BIO_puts() and the nonstandard behavior 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.
RETURN VALUES
The BIO_f_md() function returns the digest BIO method.
The BIO_set_md(), BIO_get_md(), and BIO_md_ctx() functions return 1 for
success and 0 for failure.
EXAMPLES
Create a BIO chain containing an SHA1 and MD5 digest BIO and pass 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));
Digest data by reading through a chain:
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);
Retrieve the message digests from a BIO chain and output them. This
could be used with the previous examples:
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);
SEE ALSO
TBA
BIO_f_md(3)