BIO_f_md.pod revision 225736
1=pod 2 3=head1 NAME 4 5BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx - message digest BIO filter 6 7=head1 SYNOPSIS 8 9 #include <openssl/bio.h> 10 #include <openssl/evp.h> 11 12 BIO_METHOD * BIO_f_md(void); 13 int BIO_set_md(BIO *b,EVP_MD *md); 14 int BIO_get_md(BIO *b,EVP_MD **mdp); 15 int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp); 16 17=head1 DESCRIPTION 18 19BIO_f_md() returns the message digest BIO method. This is a filter 20BIO that digests any data passed through it, it is a BIO wrapper 21for the digest routines EVP_DigestInit(), EVP_DigestUpdate() 22and EVP_DigestFinal(). 23 24Any data written or read through a digest BIO using BIO_read() and 25BIO_write() is digested. 26 27BIO_gets(), if its B<size> parameter is large enough finishes the 28digest calculation and returns the digest value. BIO_puts() is 29not supported. 30 31BIO_reset() reinitialises a digest BIO. 32 33BIO_set_md() sets the message digest of BIO B<b> to B<md>: this 34must be called to initialize a digest BIO before any data is 35passed through it. It is a BIO_ctrl() macro. 36 37BIO_get_md() places the a pointer to the digest BIOs digest method 38in B<mdp>, it is a BIO_ctrl() macro. 39 40BIO_get_md_ctx() returns the digest BIOs context into B<mdcp>. 41 42=head1 NOTES 43 44The context returned by BIO_get_md_ctx() can be used in calls 45to EVP_DigestFinal() and also the signature routines EVP_SignFinal() 46and EVP_VerifyFinal(). 47 48The context returned by BIO_get_md_ctx() is an internal context 49structure. Changes made to this context will affect the digest 50BIO itself and the context pointer will become invalid when the digest 51BIO is freed. 52 53After the digest has been retrieved from a digest BIO it must be 54reinitialized by calling BIO_reset(), or BIO_set_md() before any more 55data is passed through it. 56 57If an application needs to call BIO_gets() or BIO_puts() through 58a chain containing digest BIOs then this can be done by prepending 59a buffering BIO. 60 61=head1 RETURN VALUES 62 63BIO_f_md() returns the digest BIO method. 64 65BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and 660 for failure. 67 68=head1 EXAMPLES 69 70The following example creates a BIO chain containing an SHA1 and MD5 71digest BIO and passes the string "Hello World" through it. Error 72checking has been omitted for clarity. 73 74 BIO *bio, *mdtmp; 75 char message[] = "Hello World"; 76 bio = BIO_new(BIO_s_null()); 77 mdtmp = BIO_new(BIO_f_md()); 78 BIO_set_md(mdtmp, EVP_sha1()); 79 /* For BIO_push() we want to append the sink BIO and keep a note of 80 * the start of the chain. 81 */ 82 bio = BIO_push(mdtmp, bio); 83 mdtmp = BIO_new(BIO_f_md()); 84 BIO_set_md(mdtmp, EVP_md5()); 85 bio = BIO_push(mdtmp, bio); 86 /* Note: mdtmp can now be discarded */ 87 BIO_write(bio, message, strlen(message)); 88 89The next example digests data by reading through a chain instead: 90 91 BIO *bio, *mdtmp; 92 char buf[1024]; 93 int rdlen; 94 bio = BIO_new_file(file, "rb"); 95 mdtmp = BIO_new(BIO_f_md()); 96 BIO_set_md(mdtmp, EVP_sha1()); 97 bio = BIO_push(mdtmp, bio); 98 mdtmp = BIO_new(BIO_f_md()); 99 BIO_set_md(mdtmp, EVP_md5()); 100 bio = BIO_push(mdtmp, bio); 101 do { 102 rdlen = BIO_read(bio, buf, sizeof(buf)); 103 /* Might want to do something with the data here */ 104 } while(rdlen > 0); 105 106This next example retrieves the message digests from a BIO chain and 107outputs them. This could be used with the examples above. 108 109 BIO *mdtmp; 110 unsigned char mdbuf[EVP_MAX_MD_SIZE]; 111 int mdlen; 112 int i; 113 mdtmp = bio; /* Assume bio has previously been set up */ 114 do { 115 EVP_MD *md; 116 mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD); 117 if(!mdtmp) break; 118 BIO_get_md(mdtmp, &md); 119 printf("%s digest", OBJ_nid2sn(EVP_MD_type(md))); 120 mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE); 121 for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]); 122 printf("\n"); 123 mdtmp = BIO_next(mdtmp); 124 } while(mdtmp); 125 126 BIO_free_all(bio); 127 128=head1 BUGS 129 130The lack of support for BIO_puts() and the non standard behaviour of 131BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets() 132and BIO_puts() should be passed to the next BIO in the chain and digest 133the data passed through and that digests should be retrieved using a 134separate BIO_ctrl() call. 135 136=head1 SEE ALSO 137 138TBA 139