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, 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(X509 *x, BIO *bp);
19 int i2d_X509_fp(X509 *x, FILE *fp);
23 The X509 encode and decode routines encode and parse an
24 B<X509> structure, which represents an X509 certificate.
26 d2i_X509() attempts to decode B<len> bytes at B<*out>. If
27 successful a pointer to the B<X509> structure is returned. If an error
28 occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
29 returned structure is written to B<*px>. If B<*px> is not B<NULL>
30 then it is assumed that B<*px> contains a valid B<X509>
31 structure and an attempt is made to reuse it. If the call is
32 successful B<*out> is incremented to the byte following the
35 i2d_X509() encodes the structure pointed to by B<x> into DER format.
36 If B<out> is not B<NULL> is writes the DER encoded data to the buffer
37 at B<*out>, and increments it to point after the data just written.
38 If the return value is negative an error occurred, otherwise it
39 returns the length of the encoded data.
41 For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
42 allocated for a buffer and the encoded data written to it. In this
43 case B<*out> is not incremented and it points to the start of the
46 d2i_X509_bio() is similar to d2i_X509() except it attempts
47 to parse data from BIO B<bp>.
49 d2i_X509_fp() is similar to d2i_X509() except it attempts
50 to parse data from FILE pointer B<fp>.
52 i2d_X509_bio() is similar to i2d_X509() except it writes
53 the encoding of the structure B<x> to BIO B<bp>.
55 i2d_X509_fp() is similar to i2d_X509() except it writes
56 the encoding of the structure B<x> to BIO B<bp>.
60 The letters B<i> and B<d> in for example B<i2d_X509> stand for
61 "internal" (that is an internal C structure) and "DER". So that
62 B<i2d_X509> converts from internal to DER.
64 The functions can also understand B<BER> forms.
66 The actual X509 structure passed to i2d_X509() must be a valid
67 populated B<X509> structure it can B<not> simply be fed with an
68 empty structure such as that returned by X509_new().
70 The encoded data is in binary form and may contain embedded zeroes.
71 Therefore any FILE pointers or BIOs should be opened in binary mode.
72 Functions such as B<strlen()> will B<not> return the correct length
73 of the encoded structure.
75 The ways that B<*in> and B<*out> are incremented after the operation
76 can trap the unwary. See the B<WARNINGS> section for some common
79 The reason for the auto increment behaviour is to reflect a typical
80 usage of ASN1 functions: after one structure is encoded or decoded
81 another will processed after it.
85 Allocate and encode the DER encoding of an X509 structure:
88 unsigned char *buf, *p;
90 len = i2d_X509(x, NULL);
92 buf = OPENSSL_malloc(len);
101 If you are using OpenSSL 0.9.7 or later then this can be
110 len = i2d_X509(x, &buf);
115 Attempt to decode a buffer:
119 unsigned char *buf, *p;
123 /* Something to setup buf and len */
127 x = d2i_X509(NULL, &p, len);
132 Alternative technique:
136 unsigned char *buf, *p;
140 /* Something to setup buf and len */
146 if(!d2i_X509(&x, &p, len))
152 The use of temporary variable is mandatory. A common
153 mistake is to attempt to use a buffer directly as follows:
158 len = i2d_X509(x, NULL);
160 buf = OPENSSL_malloc(len);
167 /* Other stuff ... */
171 This code will result in B<buf> apparently containing garbage because
172 it was incremented after the call to point after the data just written.
173 Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
174 and the subsequent call to B<OPENSSL_free()> may well crash.
176 The auto allocation feature (setting buf to NULL) only works on OpenSSL
177 0.9.7 and later. Attempts to use it on earlier versions will typically
178 cause a segmentation violation.
180 Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
184 if (!d2i_X509(&x, &p, len))
187 This will probably crash somewhere in B<d2i_X509()>. The reason for this
188 is that the variable B<x> is uninitialized and an attempt will be made to
189 interpret its (invalid) value as an B<X509> structure, typically causing
190 a segmentation violation. If B<x> is set to NULL first then this will not
195 In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when
196 B<*px> is valid is broken and some parts of the reused structure may
197 persist if they are not present in the new one. As a result the use
198 of this "reuse" behaviour is strongly discouraged.
200 i2d_X509() will not return an error in many versions of OpenSSL,
201 if mandatory fields are not initialized due to a programming error
202 then the encoded structure may contain invalid data or omit the
203 fields entirely and will not be parsed by d2i_X509(). This may be
204 fixed in future so code should not assume that i2d_X509() will
209 d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
210 or B<NULL> if an error occurs. The error code that can be obtained by
211 L<ERR_get_error(3)|ERR_get_error(3)>.
213 i2d_X509(), i2d_X509_bio() and i2d_X509_fp() return a the number of bytes
214 successfully encoded or a negative value if an error occurs. The error code
215 can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
219 L<ERR_get_error(3)|ERR_get_error(3)>
223 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
224 are available in all versions of SSLeay and OpenSSL.