5 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio,
6 i2d_X509_fp - X509 encode and decode functions
10 X509 *d2i_X509(X509 **px, unsigned char **in, int len);
11 int i2d_X509(X509 *x, unsigned char **out);
13 X509 *d2i_X509_bio(BIO *bp, X509 **x);
14 X509 *d2i_X509_fp(FILE *fp, X509 **x);
16 int i2d_X509_bio(X509 *x, BIO *bp);
17 int i2d_X509_fp(X509 *x, FILE *fp);
21 The X509 encode and decode routines encode and parse an
22 B<X509> structure, which represents an X509 certificate.
24 d2i_X509() attempts to decode B<len> bytes at B<*out>. If
25 successful a pointer to the B<X509> structure is returned. If an error
26 occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
27 returned structure is written to B<*px>. If B<*px> is not B<NULL>
28 then it is assumed that B<*px> contains a valid B<X509>
29 structure and an attempt is made to reuse it. If the call is
30 successful B<*out> is incremented to the byte following the
33 i2d_X509() encodes the structure pointed to by B<x> into DER format.
34 If B<out> is not B<NULL> is writes the DER encoded data to the buffer
35 at B<*out>, and increments it to point after the data just written.
36 If the return value is negative an error occurred, otherwise it
37 returns the length of the encoded data.
39 For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
40 allocated for a buffer and the encoded data written to it. In this
41 case B<*out> is not incremented and it points to the start of the
44 d2i_X509_bio() is similar to d2i_X509() except it attempts
45 to parse data from BIO B<bp>.
47 d2i_X509_fp() is similar to d2i_X509() except it attempts
48 to parse data from FILE pointer B<fp>.
50 i2d_X509_bio() is similar to i2d_X509() except it writes
51 the encoding of the structure B<x> to BIO B<bp>.
53 i2d_X509_fp() is similar to i2d_X509() except it writes
54 the encoding of the structure B<x> to BIO B<bp>.
58 The letters B<i> and B<d> in for example B<i2d_X509> stand for
59 "internal" (that is an internal C structure) and "DER". So that
60 B<i2d_X509> converts from internal to DER.
62 The functions can also understand B<BER> forms.
64 The actual X509 structure passed to i2d_X509() must be a valid
65 populated B<X509> structure it can B<not> simply be fed with an
66 empty structure such as that returned by X509_new().
68 The encoded data is in binary form and may contain embedded zeroes.
69 Therefore any FILE pointers or BIOs should be opened in binary mode.
70 Functions such as B<strlen()> will B<not> return the correct length
71 of the encoded structure.
73 The ways that B<*in> and B<*out> are incremented after the operation
74 can trap the unwary. See the B<WARNINGS> section for some common
77 The reason for the auto increment behaviour is to reflect a typical
78 usage of ASN1 functions: after one structure is encoded or decoded
79 another will processed after it.
83 Allocate and encode the DER encoding of an X509 structure:
86 unsigned char *buf, *p;
88 len = i2d_X509(x, NULL);
90 buf = OPENSSL_malloc(len);
99 If you are using OpenSSL 0.9.7 or later then this can be
108 len = i2d_X509(x, &buf);
113 Attempt to decode a buffer:
117 unsigned char *buf, *p;
121 /* Something to setup buf and len */
125 x = d2i_X509(NULL, &p, len);
130 Alternative technique:
134 unsigned char *buf, *p;
138 /* Something to setup buf and len */
144 if(!d2i_X509(&x, &p, len))
150 The use of temporary variable is mandatory. A common
151 mistake is to attempt to use a buffer directly as follows:
156 len = i2d_X509(x, NULL);
158 buf = OPENSSL_malloc(len);
165 /* Other stuff ... */
169 This code will result in B<buf> apparently containing garbage because
170 it was incremented after the call to point after the data just written.
171 Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
172 and the subsequent call to B<OPENSSL_free()> may well crash.
174 The auto allocation feature (setting buf to NULL) only works on OpenSSL
175 0.9.7 and later. Attempts to use it on earlier versions will typically
176 cause a segmentation violation.
178 Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
182 if (!d2i_X509(&x, &p, len))
185 This will probably crash somewhere in B<d2i_X509()>. The reason for this
186 is that the variable B<x> is uninitialized and an attempt will be made to
187 interpret its (invalid) value as an B<X509> structure, typically causing
188 a segmentation violation. If B<x> is set to NULL first then this will not
193 In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when
194 B<*px> is valid is broken and some parts of the reused structure may
195 persist if they are not present in the new one. As a result the use
196 of this "reuse" behaviour is strongly discouraged.
198 i2d_X509() will not return an error in many versions of OpenSSL,
199 if mandatory fields are not initialized due to a programming error
200 then the encoded structure may contain invalid data or omit the
201 fields entirely and will not be parsed by d2i_X509(). This may be
202 fixed in future so code should not assume that i2d_X509() will
207 d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
208 or B<NULL> if an error occurs. The error code that can be obtained by
209 L<ERR_get_error(3)|ERR_get_error(3)>.
211 i2d_X509(), i2d_X509_bio() and i2d_X509_fp() return a the number of bytes
212 successfully encoded or a negative value if an error occurs. The error code
213 can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
217 L<ERR_get_error(3)|ERR_get_error(3)>
221 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
222 are available in all versions of SSLeay and OpenSSL.