d2i_X509.pod revision 306195 
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, long len);
13 X509 *d2i_X509_AUX(X509 **px, const unsigned char **in, long len);
14 int i2d_X509(X509 *x, unsigned char **out);
15 int i2d_X509_AUX(X509 *x, unsigned char **out);
16
17 X509 *d2i_X509_bio(BIO *bp, X509 **x);
18 X509 *d2i_X509_fp(FILE *fp, X509 **x);
19
20 int i2d_X509_bio(BIO *bp, X509 *x);
21 int i2d_X509_fp(FILE *fp, X509 *x);
22
23 int i2d_re_X509_tbs(X509 *x, unsigned char **out);
24
25=head1 DESCRIPTION
26
27The X509 encode and decode routines encode and parse an
28B<X509> structure, which represents an X509 certificate.
29
30d2i_X509() attempts to decode B<len> bytes at B<*in>. If 
31successful a pointer to the B<X509> structure is returned. If an error
32occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
33returned structure is written to B<*px>. If B<*px> is not B<NULL>
34then it is assumed that B<*px> contains a valid B<X509>
35structure and an attempt is made to reuse it. This "reuse" capability is present
36for historical compatibility but its use is B<strongly discouraged> (see BUGS
37below, and the discussion in the RETURN VALUES section).
38
39If the call is successful B<*in> is incremented to the byte following the
40parsed data.
41
42d2i_X509_AUX() is similar to d2i_X509() but the input is expected to consist of
43an X509 certificate followed by auxiliary trust information.
44This is used by the PEM routines to read "TRUSTED CERTIFICATE" objects.
45This function should not be called on untrusted input.
46
47i2d_X509() encodes the structure pointed to by B<x> into DER format.
48If B<out> is not B<NULL> is writes the DER encoded data to the buffer
49at B<*out>, and increments it to point after the data just written.
50If the return value is negative an error occurred, otherwise it
51returns the length of the encoded data. 
52
53For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
54allocated for a buffer and the encoded data written to it. In this
55case B<*out> is not incremented and it points to the start of the
56data just written.
57
58i2d_X509_AUX() is similar to i2d_X509(), but the encoded output contains both
59the certificate and any auxiliary trust information.
60This is used by the PEM routines to write "TRUSTED CERTIFICATE" objects.
61Note, this is a non-standard OpenSSL-specific data format.
62
63d2i_X509_bio() is similar to d2i_X509() except it attempts
64to parse data from BIO B<bp>.
65
66d2i_X509_fp() is similar to d2i_X509() except it attempts
67to parse data from FILE pointer B<fp>.
68
69i2d_X509_bio() is similar to i2d_X509() except it writes
70the encoding of the structure B<x> to BIO B<bp> and it
71returns 1 for success and 0 for failure.
72
73i2d_X509_fp() is similar to i2d_X509() except it writes
74the encoding of the structure B<x> to BIO B<bp> and it
75returns 1 for success and 0 for failure.
76
77i2d_re_X509_tbs() is similar to i2d_X509() except it encodes
78only the TBSCertificate portion of the certificate.
79
80=head1 NOTES
81
82The letters B<i> and B<d> in for example B<i2d_X509> stand for
83"internal" (that is an internal C structure) and "DER". So
84B<i2d_X509> converts from internal to DER. The "re" in
85B<i2d_re_X509_tbs> stands for "re-encode", and ensures that a fresh
86encoding is generated in case the object has been modified after
87creation (see the BUGS section).
88
89The functions can also understand B<BER> forms.
90
91The actual X509 structure passed to i2d_X509() must be a valid
92populated B<X509> structure it can B<not> simply be fed with an
93empty structure such as that returned by X509_new().
94
95The encoded data is in binary form and may contain embedded zeroes.
96Therefore any FILE pointers or BIOs should be opened in binary mode.
97Functions such as B<strlen()> will B<not> return the correct length
98of the encoded structure.
99
100The ways that B<*in> and B<*out> are incremented after the operation
101can trap the unwary. See the B<WARNINGS> section for some common
102errors.
103
104The reason for the auto increment behaviour is to reflect a typical
105usage of ASN1 functions: after one structure is encoded or decoded
106another will processed after it.
107
108=head1 EXAMPLES
109
110Allocate and encode the DER encoding of an X509 structure:
111
112 int len;
113 unsigned char *buf, *p;
114
115 len = i2d_X509(x, NULL);
116
117 buf = OPENSSL_malloc(len);
118
119 if (buf == NULL)
120	/* error */
121
122 p = buf;
123
124 i2d_X509(x, &p);
125
126If you are using OpenSSL 0.9.7 or later then this can be
127simplified to:
128
129
130 int len;
131 unsigned char *buf;
132
133 buf = NULL;
134
135 len = i2d_X509(x, &buf);
136
137 if (len < 0)
138	/* error */
139
140Attempt to decode a buffer:
141
142 X509 *x;
143
144 unsigned char *buf, *p;
145
146 int len;
147
148 /* Something to setup buf and len */
149
150 p = buf;
151
152 x = d2i_X509(NULL, &p, len);
153
154 if (x == NULL)
155    /* Some error */
156
157Alternative technique:
158
159 X509 *x;
160
161 unsigned char *buf, *p;
162
163 int len;
164
165 /* Something to setup buf and len */
166
167 p = buf;
168
169 x = NULL;
170
171 if(!d2i_X509(&x, &p, len))
172    /* Some error */
173
174
175=head1 WARNINGS
176
177The use of temporary variable is mandatory. A common
178mistake is to attempt to use a buffer directly as follows:
179
180 int len;
181 unsigned char *buf;
182
183 len = i2d_X509(x, NULL);
184
185 buf = OPENSSL_malloc(len);
186
187 if (buf == NULL)
188	/* error */
189
190 i2d_X509(x, &buf);
191
192 /* Other stuff ... */
193
194 OPENSSL_free(buf);
195
196This code will result in B<buf> apparently containing garbage because
197it was incremented after the call to point after the data just written.
198Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
199and the subsequent call to B<OPENSSL_free()> may well crash.
200
201The auto allocation feature (setting buf to NULL) only works on OpenSSL
2020.9.7 and later. Attempts to use it on earlier versions will typically
203cause a segmentation violation.
204
205Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
206
207 X509 *x;
208
209 if (!d2i_X509(&x, &p, len))
210	/* Some error */
211
212This will probably crash somewhere in B<d2i_X509()>. The reason for this
213is that the variable B<x> is uninitialized and an attempt will be made to
214interpret its (invalid) value as an B<X509> structure, typically causing
215a segmentation violation. If B<x> is set to NULL first then this will not
216happen.
217
218=head1 BUGS
219
220In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when 
221B<*px> is valid is broken and some parts of the reused structure may
222persist if they are not present in the new one. As a result the use
223of this "reuse" behaviour is strongly discouraged.
224
225i2d_X509() will not return an error in many versions of OpenSSL,
226if mandatory fields are not initialized due to a programming error
227then the encoded structure may contain invalid data or omit the
228fields entirely and will not be parsed by d2i_X509(). This may be
229fixed in future so code should not assume that i2d_X509() will
230always succeed.
231
232The encoding of the TBSCertificate portion of a certificate is cached
233in the B<X509> structure internally to improve encoding performance
234and to ensure certificate signatures are verified correctly in some
235certificates with broken (non-DER) encodings.
236
237Any function which encodes an X509 structure such as i2d_X509(),
238i2d_X509_fp() or i2d_X509_bio() may return a stale encoding if the
239B<X509> structure has been modified after deserialization or previous
240serialization.
241
242If, after modification, the B<X509> object is re-signed with X509_sign(),
243the encoding is automatically renewed. Otherwise, the encoding of the
244TBSCertificate portion of the B<X509> can be manually renewed by calling
245i2d_re_X509_tbs().
246
247=head1 RETURN VALUES
248
249d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
250or B<NULL> if an error occurs. The error code that can be obtained by
251L<ERR_get_error(3)|ERR_get_error(3)>. If the "reuse" capability has been used
252with a valid X509 structure being passed in via B<px> then the object is not
253freed in the event of error but may be in a potentially invalid or inconsistent
254state.
255
256i2d_X509() returns the number of bytes successfully encoded or a negative
257value if an error occurs. The error code can be obtained by
258L<ERR_get_error(3)|ERR_get_error(3)>. 
259
260i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error 
261occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 
262
263=head1 SEE ALSO
264
265L<ERR_get_error(3)|ERR_get_error(3)>
266
267=head1 HISTORY
268
269d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
270are available in all versions of SSLeay and OpenSSL.
271
272=cut
273