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135 .IX Title "d2i_X509 3"
136 .TH d2i_X509 3 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio,
143 i2d_X509_fp \- X509 encode and decode functions
145 .IX Header "SYNOPSIS"
147 \& #include <openssl/x509.h>
149 \& X509 *d2i_X509(X509 **px, const unsigned char **in, int len);
150 \& int i2d_X509(X509 *x, unsigned char **out);
152 \& X509 *d2i_X509_bio(BIO *bp, X509 **x);
153 \& X509 *d2i_X509_fp(FILE *fp, X509 **x);
155 \& int i2d_X509_bio(BIO *bp, X509 *x);
156 \& int i2d_X509_fp(FILE *fp, X509 *x);
158 \& int i2d_re_X509_tbs(X509 *x, unsigned char **out);
161 .IX Header "DESCRIPTION"
162 The X509 encode and decode routines encode and parse an
163 \&\fBX509\fR structure, which represents an X509 certificate.
165 \&\fId2i_X509()\fR attempts to decode \fBlen\fR bytes at \fB*in\fR. If
166 successful a pointer to the \fBX509\fR structure is returned. If an error
167 occurred then \fB\s-1NULL\s0\fR is returned. If \fBpx\fR is not \fB\s-1NULL\s0\fR then the
168 returned structure is written to \fB*px\fR. If \fB*px\fR is not \fB\s-1NULL\s0\fR
169 then it is assumed that \fB*px\fR contains a valid \fBX509\fR
170 structure and an attempt is made to reuse it. This \*(L"reuse\*(R" capability is present
171 for historical compatibility but its use is \fBstrongly discouraged\fR (see \s-1BUGS\s0
172 below, and the discussion in the \s-1RETURN VALUES\s0 section).
174 If the call is successful \fB*in\fR is incremented to the byte following the
177 \&\fIi2d_X509()\fR encodes the structure pointed to by \fBx\fR into \s-1DER\s0 format.
178 If \fBout\fR is not \fB\s-1NULL\s0\fR is writes the \s-1DER\s0 encoded data to the buffer
179 at \fB*out\fR, and increments it to point after the data just written.
180 If the return value is negative an error occurred, otherwise it
181 returns the length of the encoded data.
183 For OpenSSL 0.9.7 and later if \fB*out\fR is \fB\s-1NULL\s0\fR memory will be
184 allocated for a buffer and the encoded data written to it. In this
185 case \fB*out\fR is not incremented and it points to the start of the
188 \&\fId2i_X509_bio()\fR is similar to \fId2i_X509()\fR except it attempts
189 to parse data from \s-1BIO \s0\fBbp\fR.
191 \&\fId2i_X509_fp()\fR is similar to \fId2i_X509()\fR except it attempts
192 to parse data from \s-1FILE\s0 pointer \fBfp\fR.
194 \&\fIi2d_X509_bio()\fR is similar to \fIi2d_X509()\fR except it writes
195 the encoding of the structure \fBx\fR to \s-1BIO \s0\fBbp\fR and it
196 returns 1 for success and 0 for failure.
198 \&\fIi2d_X509_fp()\fR is similar to \fIi2d_X509()\fR except it writes
199 the encoding of the structure \fBx\fR to \s-1BIO \s0\fBbp\fR and it
200 returns 1 for success and 0 for failure.
202 \&\fIi2d_re_X509_tbs()\fR is similar to \fIi2d_X509()\fR except it encodes
203 only the TBSCertificate portion of the certificate.
206 The letters \fBi\fR and \fBd\fR in for example \fBi2d_X509\fR stand for
207 \&\*(L"internal\*(R" (that is an internal C structure) and \*(L"\s-1DER\*(R".\s0 So
208 \&\fBi2d_X509\fR converts from internal to \s-1DER.\s0 The \*(L"re\*(R" in
209 \&\fBi2d_re_X509_tbs\fR stands for \*(L"re-encode\*(R", and ensures that a fresh
210 encoding is generated in case the object has been modified after
211 creation (see the \s-1BUGS\s0 section).
213 The functions can also understand \fB\s-1BER\s0\fR forms.
215 The actual X509 structure passed to \fIi2d_X509()\fR must be a valid
216 populated \fBX509\fR structure it can \fBnot\fR simply be fed with an
217 empty structure such as that returned by \fIX509_new()\fR.
219 The encoded data is in binary form and may contain embedded zeroes.
220 Therefore any \s-1FILE\s0 pointers or BIOs should be opened in binary mode.
221 Functions such as \fB\f(BIstrlen()\fB\fR will \fBnot\fR return the correct length
222 of the encoded structure.
224 The ways that \fB*in\fR and \fB*out\fR are incremented after the operation
225 can trap the unwary. See the \fB\s-1WARNINGS\s0\fR section for some common
228 The reason for the auto increment behaviour is to reflect a typical
229 usage of \s-1ASN1\s0 functions: after one structure is encoded or decoded
230 another will processed after it.
232 .IX Header "EXAMPLES"
233 Allocate and encode the \s-1DER\s0 encoding of an X509 structure:
237 \& unsigned char *buf, *p;
239 \& len = i2d_X509(x, NULL);
241 \& buf = OPENSSL_malloc(len);
251 If you are using OpenSSL 0.9.7 or later then this can be
256 \& unsigned char *buf;
260 \& len = i2d_X509(x, &buf);
266 Attempt to decode a buffer:
271 \& unsigned char *buf, *p;
275 \& /* Something to setup buf and len */
279 \& x = d2i_X509(NULL, &p, len);
285 Alternative technique:
290 \& unsigned char *buf, *p;
294 \& /* Something to setup buf and len */
300 \& if(!d2i_X509(&x, &p, len))
304 .IX Header "WARNINGS"
305 The use of temporary variable is mandatory. A common
306 mistake is to attempt to use a buffer directly as follows:
310 \& unsigned char *buf;
312 \& len = i2d_X509(x, NULL);
314 \& buf = OPENSSL_malloc(len);
319 \& i2d_X509(x, &buf);
321 \& /* Other stuff ... */
323 \& OPENSSL_free(buf);
326 This code will result in \fBbuf\fR apparently containing garbage because
327 it was incremented after the call to point after the data just written.
328 Also \fBbuf\fR will no longer contain the pointer allocated by \fB\f(BIOPENSSL_malloc()\fB\fR
329 and the subsequent call to \fB\f(BIOPENSSL_free()\fB\fR may well crash.
331 The auto allocation feature (setting buf to \s-1NULL\s0) only works on OpenSSL
332 0.9.7 and later. Attempts to use it on earlier versions will typically
333 cause a segmentation violation.
335 Another trap to avoid is misuse of the \fBxp\fR argument to \fB\f(BId2i_X509()\fB\fR:
340 \& if (!d2i_X509(&x, &p, len))
344 This will probably crash somewhere in \fB\f(BId2i_X509()\fB\fR. The reason for this
345 is that the variable \fBx\fR is uninitialized and an attempt will be made to
346 interpret its (invalid) value as an \fBX509\fR structure, typically causing
347 a segmentation violation. If \fBx\fR is set to \s-1NULL\s0 first then this will not
351 In some versions of OpenSSL the \*(L"reuse\*(R" behaviour of \fId2i_X509()\fR when
352 \&\fB*px\fR is valid is broken and some parts of the reused structure may
353 persist if they are not present in the new one. As a result the use
354 of this \*(L"reuse\*(R" behaviour is strongly discouraged.
356 \&\fIi2d_X509()\fR will not return an error in many versions of OpenSSL,
357 if mandatory fields are not initialized due to a programming error
358 then the encoded structure may contain invalid data or omit the
359 fields entirely and will not be parsed by \fId2i_X509()\fR. This may be
360 fixed in future so code should not assume that \fIi2d_X509()\fR will
363 The encoding of the TBSCertificate portion of a certificate is cached
364 in the \fBX509\fR structure internally to improve encoding performance
365 and to ensure certificate signatures are verified correctly in some
366 certificates with broken (non-DER) encodings.
368 Any function which encodes an X509 structure such as \fIi2d_X509()\fR,
369 \&\fIi2d_X509_fp()\fR or \fIi2d_X509_bio()\fR may return a stale encoding if the
370 \&\fBX509\fR structure has been modified after deserialization or previous
373 If, after modification, the \fBX509\fR object is re-signed with \fIX509_sign()\fR,
374 the encoding is automatically renewed. Otherwise, the encoding of the
375 TBSCertificate portion of the \fBX509\fR can be manually renewed by calling
376 \&\fIi2d_re_X509_tbs()\fR.
378 .IX Header "RETURN VALUES"
379 \&\fId2i_X509()\fR, \fId2i_X509_bio()\fR and \fId2i_X509_fp()\fR return a valid \fBX509\fR structure
380 or \fB\s-1NULL\s0\fR if an error occurs. The error code that can be obtained by
381 \&\fIERR_get_error\fR\|(3). If the \*(L"reuse\*(R" capability has been used
382 with a valid X509 structure being passed in via \fBpx\fR then the object is not
383 freed in the event of error but may be in a potentially invalid or inconsistent
386 \&\fIi2d_X509()\fR returns the number of bytes successfully encoded or a negative
387 value if an error occurs. The error code can be obtained by
388 \&\fIERR_get_error\fR\|(3).
390 \&\fIi2d_X509_bio()\fR and \fIi2d_X509_fp()\fR return 1 for success and 0 if an error
391 occurs The error code can be obtained by \fIERR_get_error\fR\|(3).
393 .IX Header "SEE ALSO"
394 \&\fIERR_get_error\fR\|(3)
397 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
398 are available in all versions of SSLeay and OpenSSL.