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Diffstat (limited to 'openssl/doc/crypto/BIO_f_md.pod')
| -rw-r--r-- | openssl/doc/crypto/BIO_f_md.pod | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/openssl/doc/crypto/BIO_f_md.pod b/openssl/doc/crypto/BIO_f_md.pod new file mode 100644 index 000000000..0d24083e6 --- /dev/null +++ b/openssl/doc/crypto/BIO_f_md.pod @@ -0,0 +1,138 @@ +=pod + +=head1 NAME + +BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO filter + +=head1 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); + +=head1 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 B<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<b> to B<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 B<mdp>, it is a BIO_ctrl() macro. + +BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>. + +=head1 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. + +=head1 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. + +=head1 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); + +=head1 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. + +=head1 SEE ALSO + +TBA |