d2i_X509.pod revision 296465 
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=head1 DESCRIPTION
22
23The X509 encode and decode routines encode and parse an
24B<X509> structure, which represents an X509 certificate.
25
26d2i_X509() attempts to decode B<len> bytes at B<*in>. If 
27successful a pointer to the B<X509> structure is returned. If an error
28occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
29returned structure is written to B<*px>. If B<*px> is not B<NULL>
30then it is assumed that B<*px> contains a valid B<X509>
31structure and an attempt is made to reuse it. If the call is
32successful B<*in> is incremented to the byte following the
33parsed data.
34
35i2d_X509() encodes the structure pointed to by B<x> into DER format.
36If B<out> is not B<NULL> is writes the DER encoded data to the buffer
37at B<*out>, and increments it to point after the data just written.
38If the return value is negative an error occurred, otherwise it
39returns the length of the encoded data. 
40
41For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
42allocated for a buffer and the encoded data written to it. In this
43case B<*out> is not incremented and it points to the start of the
44data just written.
45
46d2i_X509_bio() is similar to d2i_X509() except it attempts
47to parse data from BIO B<bp>.
48
49d2i_X509_fp() is similar to d2i_X509() except it attempts
50to parse data from FILE pointer B<fp>.
51
52i2d_X509_bio() is similar to i2d_X509() except it writes
53the encoding of the structure B<x> to BIO B<bp> and it
54returns 1 for success and 0 for failure.
55
56i2d_X509_fp() is similar to i2d_X509() except it writes
57the encoding of the structure B<x> to BIO B<bp> and it
58returns 1 for success and 0 for failure.
59
60=head1 NOTES
61
62The letters B<i> and B<d> in for example B<i2d_X509> stand for
63"internal" (that is an internal C structure) and "DER". So that
64B<i2d_X509> converts from internal to DER.
65
66The functions can also understand B<BER> forms.
67
68The actual X509 structure passed to i2d_X509() must be a valid
69populated B<X509> structure it can B<not> simply be fed with an
70empty structure such as that returned by X509_new().
71
72The encoded data is in binary form and may contain embedded zeroes.
73Therefore any FILE pointers or BIOs should be opened in binary mode.
74Functions such as B<strlen()> will B<not> return the correct length
75of the encoded structure.
76
77The ways that B<*in> and B<*out> are incremented after the operation
78can trap the unwary. See the B<WARNINGS> section for some common
79errors.
80
81The reason for the auto increment behaviour is to reflect a typical
82usage of ASN1 functions: after one structure is encoded or decoded
83another will processed after it.
84
85=head1 EXAMPLES
86
87Allocate and encode the DER encoding of an X509 structure:
88
89 int len;
90 unsigned char *buf, *p;
91
92 len = i2d_X509(x, NULL);
93
94 buf = OPENSSL_malloc(len);
95
96 if (buf == NULL)
97	/* error */
98
99 p = buf;
100
101 i2d_X509(x, &p);
102
103If you are using OpenSSL 0.9.7 or later then this can be
104simplified to:
105
106
107 int len;
108 unsigned char *buf;
109
110 buf = NULL;
111
112 len = i2d_X509(x, &buf);
113
114 if (len < 0)
115	/* error */
116
117Attempt to decode a buffer:
118
119 X509 *x;
120
121 unsigned char *buf, *p;
122
123 int len;
124
125 /* Something to setup buf and len */
126
127 p = buf;
128
129 x = d2i_X509(NULL, &p, len);
130
131 if (x == NULL)
132    /* Some error */
133
134Alternative technique:
135
136 X509 *x;
137
138 unsigned char *buf, *p;
139
140 int len;
141
142 /* Something to setup buf and len */
143
144 p = buf;
145
146 x = NULL;
147
148 if(!d2i_X509(&x, &p, len))
149    /* Some error */
150
151
152=head1 WARNINGS
153
154The use of temporary variable is mandatory. A common
155mistake is to attempt to use a buffer directly as follows:
156
157 int len;
158 unsigned char *buf;
159
160 len = i2d_X509(x, NULL);
161
162 buf = OPENSSL_malloc(len);
163
164 if (buf == NULL)
165	/* error */
166
167 i2d_X509(x, &buf);
168
169 /* Other stuff ... */
170
171 OPENSSL_free(buf);
172
173This code will result in B<buf> apparently containing garbage because
174it was incremented after the call to point after the data just written.
175Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
176and the subsequent call to B<OPENSSL_free()> may well crash.
177
178The auto allocation feature (setting buf to NULL) only works on OpenSSL
1790.9.7 and later. Attempts to use it on earlier versions will typically
180cause a segmentation violation.
181
182Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
183
184 X509 *x;
185
186 if (!d2i_X509(&x, &p, len))
187	/* Some error */
188
189This will probably crash somewhere in B<d2i_X509()>. The reason for this
190is that the variable B<x> is uninitialized and an attempt will be made to
191interpret its (invalid) value as an B<X509> structure, typically causing
192a segmentation violation. If B<x> is set to NULL first then this will not
193happen.
194
195=head1 BUGS
196
197In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when 
198B<*px> is valid is broken and some parts of the reused structure may
199persist if they are not present in the new one. As a result the use
200of this "reuse" behaviour is strongly discouraged.
201
202i2d_X509() will not return an error in many versions of OpenSSL,
203if mandatory fields are not initialized due to a programming error
204then the encoded structure may contain invalid data or omit the
205fields entirely and will not be parsed by d2i_X509(). This may be
206fixed in future so code should not assume that i2d_X509() will
207always succeed.
208
209=head1 RETURN VALUES
210
211d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
212or B<NULL> if an error occurs. The error code that can be obtained by
213L<ERR_get_error(3)|ERR_get_error(3)>. 
214
215i2d_X509() returns the number of bytes successfully encoded or a negative
216value if an error occurs. The error code can be obtained by
217L<ERR_get_error(3)|ERR_get_error(3)>. 
218
219i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error 
220occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 
221
222=head1 SEE ALSO
223
224L<ERR_get_error(3)|ERR_get_error(3)>
225
226=head1 HISTORY
227
228d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
229are available in all versions of SSLeay and OpenSSL.
230
231=cut
232