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 61Before OpenSSL 1.0.0 the call to BIO_get_md_ctx() would only work if the BIO 62had been initialized for example by calling BIO_set_md() ). In OpenSSL 631.0.0 and later the context is always returned and the BIO is state is set 64to initialized. This allows applications to initialize the context externally 65if the standard calls such as BIO_set_md() are not sufficiently flexible. 66 67=head1 RETURN VALUES 68 69BIO_f_md() returns the digest BIO method. 70 71BIO_set_md(), BIO_get_md() and BIO_md_ctx() return 1 for success and 720 for failure. 73 74=head1 EXAMPLES 75 76The following example creates a BIO chain containing an SHA1 and MD5 77digest BIO and passes the string "Hello World" through it. Error 78checking has been omitted for clarity. 79 80 BIO *bio, *mdtmp; 81 char message[] = "Hello World"; 82 bio = BIO_new(BIO_s_null()); 83 mdtmp = BIO_new(BIO_f_md()); 84 BIO_set_md(mdtmp, EVP_sha1()); 85 /* For BIO_push() we want to append the sink BIO and keep a note of 86 * the start of the chain. 87 */ 88 bio = BIO_push(mdtmp, bio); 89 mdtmp = BIO_new(BIO_f_md()); 90 BIO_set_md(mdtmp, EVP_md5()); 91 bio = BIO_push(mdtmp, bio); 92 /* Note: mdtmp can now be discarded */ 93 BIO_write(bio, message, strlen(message)); 94 95The next example digests data by reading through a chain instead: 96 97 BIO *bio, *mdtmp; 98 char buf[1024]; 99 int rdlen; 100 bio = BIO_new_file(file, "rb"); 101 mdtmp = BIO_new(BIO_f_md()); 102 BIO_set_md(mdtmp, EVP_sha1()); 103 bio = BIO_push(mdtmp, bio); 104 mdtmp = BIO_new(BIO_f_md()); 105 BIO_set_md(mdtmp, EVP_md5()); 106 bio = BIO_push(mdtmp, bio); 107 do { 108 rdlen = BIO_read(bio, buf, sizeof(buf)); 109 /* Might want to do something with the data here */ 110 } while(rdlen > 0); 111 112This next example retrieves the message digests from a BIO chain and 113outputs them. This could be used with the examples above. 114 115 BIO *mdtmp; 116 unsigned char mdbuf[EVP_MAX_MD_SIZE]; 117 int mdlen; 118 int i; 119 mdtmp = bio; /* Assume bio has previously been set up */ 120 do { 121 EVP_MD *md; 122 mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD); 123 if(!mdtmp) break; 124 BIO_get_md(mdtmp, &md); 125 printf("%s digest", OBJ_nid2sn(EVP_MD_type(md))); 126 mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE); 127 for(i = 0; i < mdlen; i++) printf(":%02X", mdbuf[i]); 128 printf("\n"); 129 mdtmp = BIO_next(mdtmp); 130 } while(mdtmp); 131 132 BIO_free_all(bio); 133 134=head1 BUGS 135 136The lack of support for BIO_puts() and the non standard behaviour of 137BIO_gets() could be regarded as anomalous. It could be argued that BIO_gets() 138and BIO_puts() should be passed to the next BIO in the chain and digest 139the data passed through and that digests should be retrieved using a 140separate BIO_ctrl() call. 141 142=head1 SEE ALSO 143 144TBA 145