1=pod 2 3=head1 NAME 4 5d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio, 6i2d_X509_fp - X509 encode and decode functions 7 8=head1 SYNOPSIS 9 10 #include <openssl/x509.h> 11 12 X509 *d2i_X509(X509 **px, const unsigned char **in, int len); 13 int i2d_X509(X509 *x, unsigned char **out); 14 15 X509 *d2i_X509_bio(BIO *bp, X509 **x); 16 X509 *d2i_X509_fp(FILE *fp, X509 **x); 17 18 int i2d_X509_bio(BIO *bp, X509 *x); 19 int i2d_X509_fp(FILE *fp, X509 *x); 20 21 int i2d_re_X509_tbs(X509 *x, unsigned char **out); 22 23=head1 DESCRIPTION 24 25The X509 encode and decode routines encode and parse an 26B<X509> structure, which represents an X509 certificate. 27 28d2i_X509() attempts to decode B<len> bytes at B<*in>. If 29successful a pointer to the B<X509> structure is returned. If an error 30occurred then B<NULL> is returned. If B<px> is not B<NULL> then the 31returned structure is written to B<*px>. If B<*px> is not B<NULL> 32then it is assumed that B<*px> contains a valid B<X509> 33structure and an attempt is made to reuse it. This "reuse" capability is present 34for historical compatibility but its use is B<strongly discouraged> (see BUGS 35below, and the discussion in the RETURN VALUES section). 36 37If the call is successful B<*in> is incremented to the byte following the 38parsed data. 39 40i2d_X509() encodes the structure pointed to by B<x> into DER format. 41If B<out> is not B<NULL> is writes the DER encoded data to the buffer 42at B<*out>, and increments it to point after the data just written. 43If the return value is negative an error occurred, otherwise it 44returns the length of the encoded data. 45 46For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be 47allocated for a buffer and the encoded data written to it. In this 48case B<*out> is not incremented and it points to the start of the 49data just written. 50 51d2i_X509_bio() is similar to d2i_X509() except it attempts 52to parse data from BIO B<bp>. 53 54d2i_X509_fp() is similar to d2i_X509() except it attempts 55to parse data from FILE pointer B<fp>. 56 57i2d_X509_bio() is similar to i2d_X509() except it writes 58the encoding of the structure B<x> to BIO B<bp> and it 59returns 1 for success and 0 for failure. 60 61i2d_X509_fp() is similar to i2d_X509() except it writes 62the encoding of the structure B<x> to BIO B<bp> and it 63returns 1 for success and 0 for failure. 64 65i2d_re_X509_tbs() is similar to i2d_X509() except it encodes 66only the TBSCertificate portion of the certificate. 67 68=head1 NOTES 69 70The letters B<i> and B<d> in for example B<i2d_X509> stand for 71"internal" (that is an internal C structure) and "DER". So 72B<i2d_X509> converts from internal to DER. The "re" in 73B<i2d_re_X509_tbs> stands for "re-encode", and ensures that a fresh 74encoding is generated in case the object has been modified after 75creation (see the BUGS section). 76 77The functions can also understand B<BER> forms. 78 79The actual X509 structure passed to i2d_X509() must be a valid 80populated B<X509> structure it can B<not> simply be fed with an 81empty structure such as that returned by X509_new(). 82 83The encoded data is in binary form and may contain embedded zeroes. 84Therefore any FILE pointers or BIOs should be opened in binary mode. 85Functions such as B<strlen()> will B<not> return the correct length 86of the encoded structure. 87 88The ways that B<*in> and B<*out> are incremented after the operation 89can trap the unwary. See the B<WARNINGS> section for some common 90errors. 91 92The reason for the auto increment behaviour is to reflect a typical 93usage of ASN1 functions: after one structure is encoded or decoded 94another will processed after it. 95 96=head1 EXAMPLES 97 98Allocate and encode the DER encoding of an X509 structure: 99 100 int len; 101 unsigned char *buf, *p; 102 103 len = i2d_X509(x, NULL); 104 105 buf = OPENSSL_malloc(len); 106 107 if (buf == NULL) 108 /* error */ 109 110 p = buf; 111 112 i2d_X509(x, &p); 113 114If you are using OpenSSL 0.9.7 or later then this can be 115simplified to: 116 117 118 int len; 119 unsigned char *buf; 120 121 buf = NULL; 122 123 len = i2d_X509(x, &buf); 124 125 if (len < 0) 126 /* error */ 127 128Attempt to decode a buffer: 129 130 X509 *x; 131 132 unsigned char *buf, *p; 133 134 int len; 135 136 /* Something to setup buf and len */ 137 138 p = buf; 139 140 x = d2i_X509(NULL, &p, len); 141 142 if (x == NULL) 143 /* Some error */ 144 145Alternative technique: 146 147 X509 *x; 148 149 unsigned char *buf, *p; 150 151 int len; 152 153 /* Something to setup buf and len */ 154 155 p = buf; 156 157 x = NULL; 158 159 if(!d2i_X509(&x, &p, len)) 160 /* Some error */ 161 162 163=head1 WARNINGS 164 165The use of temporary variable is mandatory. A common 166mistake is to attempt to use a buffer directly as follows: 167 168 int len; 169 unsigned char *buf; 170 171 len = i2d_X509(x, NULL); 172 173 buf = OPENSSL_malloc(len); 174 175 if (buf == NULL) 176 /* error */ 177 178 i2d_X509(x, &buf); 179 180 /* Other stuff ... */ 181 182 OPENSSL_free(buf); 183 184This code will result in B<buf> apparently containing garbage because 185it was incremented after the call to point after the data just written. 186Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()> 187and the subsequent call to B<OPENSSL_free()> may well crash. 188 189The auto allocation feature (setting buf to NULL) only works on OpenSSL 1900.9.7 and later. Attempts to use it on earlier versions will typically 191cause a segmentation violation. 192 193Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>: 194 195 X509 *x; 196 197 if (!d2i_X509(&x, &p, len)) 198 /* Some error */ 199 200This will probably crash somewhere in B<d2i_X509()>. The reason for this 201is that the variable B<x> is uninitialized and an attempt will be made to 202interpret its (invalid) value as an B<X509> structure, typically causing 203a segmentation violation. If B<x> is set to NULL first then this will not 204happen. 205 206=head1 BUGS 207 208In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when 209B<*px> is valid is broken and some parts of the reused structure may 210persist if they are not present in the new one. As a result the use 211of this "reuse" behaviour is strongly discouraged. 212 213i2d_X509() will not return an error in many versions of OpenSSL, 214if mandatory fields are not initialized due to a programming error 215then the encoded structure may contain invalid data or omit the 216fields entirely and will not be parsed by d2i_X509(). This may be 217fixed in future so code should not assume that i2d_X509() will 218always succeed. 219 220The encoding of the TBSCertificate portion of a certificate is cached 221in the B<X509> structure internally to improve encoding performance 222and to ensure certificate signatures are verified correctly in some 223certificates with broken (non-DER) encodings. 224 225Any function which encodes an X509 structure such as i2d_X509(), 226i2d_X509_fp() or i2d_X509_bio() may return a stale encoding if the 227B<X509> structure has been modified after deserialization or previous 228serialization. 229 230If, after modification, the B<X509> object is re-signed with X509_sign(), 231the encoding is automatically renewed. Otherwise, the encoding of the 232TBSCertificate portion of the B<X509> can be manually renewed by calling 233i2d_re_X509_tbs(). 234 235=head1 RETURN VALUES 236 237d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure 238or B<NULL> if an error occurs. The error code that can be obtained by 239L<ERR_get_error(3)|ERR_get_error(3)>. If the "reuse" capability has been used 240with a valid X509 structure being passed in via B<px> then the object is not 241freed in the event of error but may be in a potentially invalid or inconsistent 242state. 243 244i2d_X509() returns the number of bytes successfully encoded or a negative 245value if an error occurs. The error code can be obtained by 246L<ERR_get_error(3)|ERR_get_error(3)>. 247 248i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error 249occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 250 251=head1 SEE ALSO 252 253L<ERR_get_error(3)|ERR_get_error(3)> 254 255=head1 HISTORY 256 257d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp 258are available in all versions of SSLeay and OpenSSL. 259 260=cut 261