5 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio,
6 i2d_X509_fp - X509 encode and decode functions
10 #include <openssl/x509.h>
12 X509 *d2i_X509(X509 **px, const unsigned char **in, int len);
13 int i2d_X509(X509 *x, unsigned char **out);
15 X509 *d2i_X509_bio(BIO *bp, X509 **x);
16 X509 *d2i_X509_fp(FILE *fp, X509 **x);
18 int i2d_X509_bio(BIO *bp, X509 *x);
19 int i2d_X509_fp(FILE *fp, X509 *x);
21 int i2d_re_X509_tbs(X509 *x, unsigned char **out);
25 The X509 encode and decode routines encode and parse an
26 B<X509> structure, which represents an X509 certificate.
28 d2i_X509() attempts to decode B<len> bytes at B<*in>. If
29 successful a pointer to the B<X509> structure is returned. If an error
30 occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
31 returned structure is written to B<*px>. If B<*px> is not B<NULL>
32 then it is assumed that B<*px> contains a valid B<X509>
33 structure and an attempt is made to reuse it. If the call is
34 successful B<*in> is incremented to the byte following the
37 i2d_X509() encodes the structure pointed to by B<x> into DER format.
38 If B<out> is not B<NULL> is writes the DER encoded data to the buffer
39 at B<*out>, and increments it to point after the data just written.
40 If the return value is negative an error occurred, otherwise it
41 returns the length of the encoded data.
43 For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
44 allocated for a buffer and the encoded data written to it. In this
45 case B<*out> is not incremented and it points to the start of the
48 d2i_X509_bio() is similar to d2i_X509() except it attempts
49 to parse data from BIO B<bp>.
51 d2i_X509_fp() is similar to d2i_X509() except it attempts
52 to parse data from FILE pointer B<fp>.
54 i2d_X509_bio() is similar to i2d_X509() except it writes
55 the encoding of the structure B<x> to BIO B<bp> and it
56 returns 1 for success and 0 for failure.
58 i2d_X509_fp() is similar to i2d_X509() except it writes
59 the encoding of the structure B<x> to BIO B<bp> and it
60 returns 1 for success and 0 for failure.
62 i2d_re_X509_tbs() is similar to i2d_X509() except it encodes
63 only the TBSCertificate portion of the certificate.
67 The letters B<i> and B<d> in for example B<i2d_X509> stand for
68 "internal" (that is an internal C structure) and "DER". So
69 B<i2d_X509> converts from internal to DER. The "re" in
70 B<i2d_re_X509_tbs> stands for "re-encode", and ensures that a fresh
71 encoding is generated in case the object has been modified after
72 creation (see the BUGS section).
74 The functions can also understand B<BER> forms.
76 The actual X509 structure passed to i2d_X509() must be a valid
77 populated B<X509> structure it can B<not> simply be fed with an
78 empty structure such as that returned by X509_new().
80 The encoded data is in binary form and may contain embedded zeroes.
81 Therefore any FILE pointers or BIOs should be opened in binary mode.
82 Functions such as B<strlen()> will B<not> return the correct length
83 of the encoded structure.
85 The ways that B<*in> and B<*out> are incremented after the operation
86 can trap the unwary. See the B<WARNINGS> section for some common
89 The reason for the auto increment behaviour is to reflect a typical
90 usage of ASN1 functions: after one structure is encoded or decoded
91 another will processed after it.
95 Allocate and encode the DER encoding of an X509 structure:
98 unsigned char *buf, *p;
100 len = i2d_X509(x, NULL);
102 buf = OPENSSL_malloc(len);
111 If you are using OpenSSL 0.9.7 or later then this can be
120 len = i2d_X509(x, &buf);
125 Attempt to decode a buffer:
129 unsigned char *buf, *p;
133 /* Something to setup buf and len */
137 x = d2i_X509(NULL, &p, len);
142 Alternative technique:
146 unsigned char *buf, *p;
150 /* Something to setup buf and len */
156 if(!d2i_X509(&x, &p, len))
162 The use of temporary variable is mandatory. A common
163 mistake is to attempt to use a buffer directly as follows:
168 len = i2d_X509(x, NULL);
170 buf = OPENSSL_malloc(len);
177 /* Other stuff ... */
181 This code will result in B<buf> apparently containing garbage because
182 it was incremented after the call to point after the data just written.
183 Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
184 and the subsequent call to B<OPENSSL_free()> may well crash.
186 The auto allocation feature (setting buf to NULL) only works on OpenSSL
187 0.9.7 and later. Attempts to use it on earlier versions will typically
188 cause a segmentation violation.
190 Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
194 if (!d2i_X509(&x, &p, len))
197 This will probably crash somewhere in B<d2i_X509()>. The reason for this
198 is that the variable B<x> is uninitialized and an attempt will be made to
199 interpret its (invalid) value as an B<X509> structure, typically causing
200 a segmentation violation. If B<x> is set to NULL first then this will not
205 In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when
206 B<*px> is valid is broken and some parts of the reused structure may
207 persist if they are not present in the new one. As a result the use
208 of this "reuse" behaviour is strongly discouraged.
210 i2d_X509() will not return an error in many versions of OpenSSL,
211 if mandatory fields are not initialized due to a programming error
212 then the encoded structure may contain invalid data or omit the
213 fields entirely and will not be parsed by d2i_X509(). This may be
214 fixed in future so code should not assume that i2d_X509() will
217 The encoding of the TBSCertificate portion of a certificate is cached
218 in the B<X509> structure internally to improve encoding performance
219 and to ensure certificate signatures are verified correctly in some
220 certificates with broken (non-DER) encodings.
222 Any function which encodes an X509 structure such as i2d_X509(),
223 i2d_X509_fp() or i2d_X509_bio() may return a stale encoding if the
224 B<X509> structure has been modified after deserialization or previous
227 If, after modification, the B<X509> object is re-signed with X509_sign(),
228 the encoding is automatically renewed. Otherwise, the encoding of the
229 TBSCertificate portion of the B<X509> can be manually renewed by calling
234 d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
235 or B<NULL> if an error occurs. The error code that can be obtained by
236 L<ERR_get_error(3)|ERR_get_error(3)>.
238 i2d_X509() returns the number of bytes successfully encoded or a negative
239 value if an error occurs. The error code can be obtained by
240 L<ERR_get_error(3)|ERR_get_error(3)>.
242 i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error
243 occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
247 L<ERR_get_error(3)|ERR_get_error(3)>
251 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
252 are available in all versions of SSLeay and OpenSSL.