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Title "BIO_f_md 3"
way too many mistakes in technical documents.
.nh
Any data written or read through a digest \s-1BIO\s0 using BIO_read_ex() and \fBBIO_write_ex() is digested.
\fBBIO_gets(), if its size parameter is large enough finishes the digest calculation and returns the digest value. BIO_puts() is not supported.
\fBBIO_reset() reinitialises a digest \s-1BIO.\s0
\fBBIO_set_md() sets the message digest of \s-1BIO\s0 b to md: this must be called to initialize a digest \s-1BIO\s0 before any data is passed through it. It is a BIO_ctrl() macro.
\fBBIO_get_md() places the a pointer to the digest BIOs digest method in mdp, it is a BIO_ctrl() macro.
\fBBIO_get_md_ctx() returns the digest BIOs context into mdcp.
The context returned by BIO_get_md_ctx() 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.
After the digest has been retrieved from a digest \s-1BIO\s0 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 \s-1BIO.\s0
Calling BIO_get_md_ctx() 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 BIO_set_md() are not sufficiently flexible.
\fBBIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and 0 for failure.
.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
The next example digests data by reading through a chain instead:
.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
This next example retrieves the message digests from a \s-1BIO\s0 chain and outputs them. This could be used with the examples above.
.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
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>.
Indexes created Mon Apr 27 00:23:16 UTC 2026