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, int len);
13 int i2d_X509(X509 *x, unsigned char **out);
14
15 X509 *d2i_X509_bio(BIO *bp, X509 **x);
16 X509 *d2i_X509_fp(FILE *fp, X509 **x);
17
18 int i2d_X509_bio(BIO *bp, X509 *x);
19 int i2d_X509_fp(FILE *fp, X509 *x);
20
21 int i2d_re_X509_tbs(X509 *x, unsigned char **out);
22
23=head1 DESCRIPTION
24
25The X509 encode and decode routines encode and parse an
26B<X509> structure, which represents an X509 certificate.
27
28d2i_X509() attempts to decode B<len> bytes at B<*in>. If 
29successful a pointer to the B<X509> structure is returned. If an error
30occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
31returned structure is written to B<*px>. If B<*px> is not B<NULL>
32then it is assumed that B<*px> contains a valid B<X509>
33structure and an attempt is made to reuse it. This "reuse" capability is present
34for historical compatibility but its use is B<strongly discouraged> (see BUGS
35below, and the discussion in the RETURN VALUES section).
36
37If the call is successful B<*in> is incremented to the byte following the
38parsed data.
39
40i2d_X509() encodes the structure pointed to by B<x> into DER format.
41If B<out> is not B<NULL> is writes the DER encoded data to the buffer
42at B<*out>, and increments it to point after the data just written.
43If the return value is negative an error occurred, otherwise it
44returns the length of the encoded data. 
45
46For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
47allocated for a buffer and the encoded data written to it. In this
48case B<*out> is not incremented and it points to the start of the
49data just written.
50
51d2i_X509_bio() is similar to d2i_X509() except it attempts
52to parse data from BIO B<bp>.
53
54d2i_X509_fp() is similar to d2i_X509() except it attempts
55to parse data from FILE pointer B<fp>.
56
57i2d_X509_bio() is similar to i2d_X509() except it writes
58the encoding of the structure B<x> to BIO B<bp> and it
59returns 1 for success and 0 for failure.
60
61i2d_X509_fp() is similar to i2d_X509() except it writes
62the encoding of the structure B<x> to BIO B<bp> and it
63returns 1 for success and 0 for failure.
64
65i2d_re_X509_tbs() is similar to i2d_X509() except it encodes
66only the TBSCertificate portion of the certificate.
67
68=head1 NOTES
69
70The letters B<i> and B<d> in for example B<i2d_X509> stand for
71"internal" (that is an internal C structure) and "DER". So
72B<i2d_X509> converts from internal to DER. The "re" in
73B<i2d_re_X509_tbs> stands for "re-encode", and ensures that a fresh
74encoding is generated in case the object has been modified after
75creation (see the BUGS section).
76
77The functions can also understand B<BER> forms.
78
79The actual X509 structure passed to i2d_X509() must be a valid
80populated B<X509> structure it can B<not> simply be fed with an
81empty structure such as that returned by X509_new().
82
83The encoded data is in binary form and may contain embedded zeroes.
84Therefore any FILE pointers or BIOs should be opened in binary mode.
85Functions such as B<strlen()> will B<not> return the correct length
86of the encoded structure.
87
88The ways that B<*in> and B<*out> are incremented after the operation
89can trap the unwary. See the B<WARNINGS> section for some common
90errors.
91
92The reason for the auto increment behaviour is to reflect a typical
93usage of ASN1 functions: after one structure is encoded or decoded
94another will processed after it.
95
96=head1 EXAMPLES
97
98Allocate and encode the DER encoding of an X509 structure:
99
100 int len;
101 unsigned char *buf, *p;
102
103 len = i2d_X509(x, NULL);
104
105 buf = OPENSSL_malloc(len);
106
107 if (buf == NULL)
108	/* error */
109
110 p = buf;
111
112 i2d_X509(x, &p);
113
114If you are using OpenSSL 0.9.7 or later then this can be
115simplified to:
116
117
118 int len;
119 unsigned char *buf;
120
121 buf = NULL;
122
123 len = i2d_X509(x, &buf);
124
125 if (len < 0)
126	/* error */
127
128Attempt to decode a buffer:
129
130 X509 *x;
131
132 unsigned char *buf, *p;
133
134 int len;
135
136 /* Something to setup buf and len */
137
138 p = buf;
139
140 x = d2i_X509(NULL, &p, len);
141
142 if (x == NULL)
143    /* Some error */
144
145Alternative technique:
146
147 X509 *x;
148
149 unsigned char *buf, *p;
150
151 int len;
152
153 /* Something to setup buf and len */
154
155 p = buf;
156
157 x = NULL;
158
159 if(!d2i_X509(&x, &p, len))
160    /* Some error */
161
162
163=head1 WARNINGS
164
165The use of temporary variable is mandatory. A common
166mistake is to attempt to use a buffer directly as follows:
167
168 int len;
169 unsigned char *buf;
170
171 len = i2d_X509(x, NULL);
172
173 buf = OPENSSL_malloc(len);
174
175 if (buf == NULL)
176	/* error */
177
178 i2d_X509(x, &buf);
179
180 /* Other stuff ... */
181
182 OPENSSL_free(buf);
183
184This code will result in B<buf> apparently containing garbage because
185it was incremented after the call to point after the data just written.
186Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
187and the subsequent call to B<OPENSSL_free()> may well crash.
188
189The auto allocation feature (setting buf to NULL) only works on OpenSSL
1900.9.7 and later. Attempts to use it on earlier versions will typically
191cause a segmentation violation.
192
193Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
194
195 X509 *x;
196
197 if (!d2i_X509(&x, &p, len))
198	/* Some error */
199
200This will probably crash somewhere in B<d2i_X509()>. The reason for this
201is that the variable B<x> is uninitialized and an attempt will be made to
202interpret its (invalid) value as an B<X509> structure, typically causing
203a segmentation violation. If B<x> is set to NULL first then this will not
204happen.
205
206=head1 BUGS
207
208In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when 
209B<*px> is valid is broken and some parts of the reused structure may
210persist if they are not present in the new one. As a result the use
211of this "reuse" behaviour is strongly discouraged.
212
213i2d_X509() will not return an error in many versions of OpenSSL,
214if mandatory fields are not initialized due to a programming error
215then the encoded structure may contain invalid data or omit the
216fields entirely and will not be parsed by d2i_X509(). This may be
217fixed in future so code should not assume that i2d_X509() will
218always succeed.
219
220The encoding of the TBSCertificate portion of a certificate is cached
221in the B<X509> structure internally to improve encoding performance
222and to ensure certificate signatures are verified correctly in some
223certificates with broken (non-DER) encodings.
224
225Any function which encodes an X509 structure such as i2d_X509(),
226i2d_X509_fp() or i2d_X509_bio() may return a stale encoding if the
227B<X509> structure has been modified after deserialization or previous
228serialization.
229
230If, after modification, the B<X509> object is re-signed with X509_sign(),
231the encoding is automatically renewed. Otherwise, the encoding of the
232TBSCertificate portion of the B<X509> can be manually renewed by calling
233i2d_re_X509_tbs().
234
235=head1 RETURN VALUES
236
237d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
238or B<NULL> if an error occurs. The error code that can be obtained by
239L<ERR_get_error(3)|ERR_get_error(3)>. If the "reuse" capability has been used
240with a valid X509 structure being passed in via B<px> then the object is not
241freed in the event of error but may be in a potentially invalid or inconsistent
242state.
243
244i2d_X509() returns the number of bytes successfully encoded or a negative
245value if an error occurs. The error code can be obtained by
246L<ERR_get_error(3)|ERR_get_error(3)>. 
247
248i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error 
249occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 
250
251=head1 SEE ALSO
252
253L<ERR_get_error(3)|ERR_get_error(3)>
254
255=head1 HISTORY
256
257d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
258are available in all versions of SSLeay and OpenSSL.
259
260=cut
261