d2i_X509.pod revision 296341 
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. This "reuse" capability is present
32for historical compatibility but its use is B<strongly discouraged> (see BUGS
33below, and the discussion in the RETURN VALUES section).
34
35If the call is successful B<*in> is incremented to the byte following the
36parsed data.
37
38i2d_X509() encodes the structure pointed to by B<x> into DER format.
39If B<out> is not B<NULL> is writes the DER encoded data to the buffer
40at B<*out>, and increments it to point after the data just written.
41If the return value is negative an error occurred, otherwise it
42returns the length of the encoded data. 
43
44For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
45allocated for a buffer and the encoded data written to it. In this
46case B<*out> is not incremented and it points to the start of the
47data just written.
48
49d2i_X509_bio() is similar to d2i_X509() except it attempts
50to parse data from BIO B<bp>.
51
52d2i_X509_fp() is similar to d2i_X509() except it attempts
53to parse data from FILE pointer B<fp>.
54
55i2d_X509_bio() is similar to i2d_X509() except it writes
56the encoding of the structure B<x> to BIO B<bp> and it
57returns 1 for success and 0 for failure.
58
59i2d_X509_fp() is similar to i2d_X509() except it writes
60the encoding of the structure B<x> to BIO B<bp> and it
61returns 1 for success and 0 for failure.
62
63=head1 NOTES
64
65The letters B<i> and B<d> in for example B<i2d_X509> stand for
66"internal" (that is an internal C structure) and "DER". So that
67B<i2d_X509> converts from internal to DER.
68
69The functions can also understand B<BER> forms.
70
71The actual X509 structure passed to i2d_X509() must be a valid
72populated B<X509> structure it can B<not> simply be fed with an
73empty structure such as that returned by X509_new().
74
75The encoded data is in binary form and may contain embedded zeroes.
76Therefore any FILE pointers or BIOs should be opened in binary mode.
77Functions such as B<strlen()> will B<not> return the correct length
78of the encoded structure.
79
80The ways that B<*in> and B<*out> are incremented after the operation
81can trap the unwary. See the B<WARNINGS> section for some common
82errors.
83
84The reason for the auto increment behaviour is to reflect a typical
85usage of ASN1 functions: after one structure is encoded or decoded
86another will processed after it.
87
88=head1 EXAMPLES
89
90Allocate and encode the DER encoding of an X509 structure:
91
92 int len;
93 unsigned char *buf, *p;
94
95 len = i2d_X509(x, NULL);
96
97 buf = OPENSSL_malloc(len);
98
99 if (buf == NULL)
100	/* error */
101
102 p = buf;
103
104 i2d_X509(x, &p);
105
106If you are using OpenSSL 0.9.7 or later then this can be
107simplified to:
108
109
110 int len;
111 unsigned char *buf;
112
113 buf = NULL;
114
115 len = i2d_X509(x, &buf);
116
117 if (len < 0)
118	/* error */
119
120Attempt to decode a buffer:
121
122 X509 *x;
123
124 unsigned char *buf, *p;
125
126 int len;
127
128 /* Something to setup buf and len */
129
130 p = buf;
131
132 x = d2i_X509(NULL, &p, len);
133
134 if (x == NULL)
135    /* Some error */
136
137Alternative technique:
138
139 X509 *x;
140
141 unsigned char *buf, *p;
142
143 int len;
144
145 /* Something to setup buf and len */
146
147 p = buf;
148
149 x = NULL;
150
151 if(!d2i_X509(&x, &p, len))
152    /* Some error */
153
154
155=head1 WARNINGS
156
157The use of temporary variable is mandatory. A common
158mistake is to attempt to use a buffer directly as follows:
159
160 int len;
161 unsigned char *buf;
162
163 len = i2d_X509(x, NULL);
164
165 buf = OPENSSL_malloc(len);
166
167 if (buf == NULL)
168	/* error */
169
170 i2d_X509(x, &buf);
171
172 /* Other stuff ... */
173
174 OPENSSL_free(buf);
175
176This code will result in B<buf> apparently containing garbage because
177it was incremented after the call to point after the data just written.
178Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
179and the subsequent call to B<OPENSSL_free()> may well crash.
180
181The auto allocation feature (setting buf to NULL) only works on OpenSSL
1820.9.7 and later. Attempts to use it on earlier versions will typically
183cause a segmentation violation.
184
185Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
186
187 X509 *x;
188
189 if (!d2i_X509(&x, &p, len))
190	/* Some error */
191
192This will probably crash somewhere in B<d2i_X509()>. The reason for this
193is that the variable B<x> is uninitialized and an attempt will be made to
194interpret its (invalid) value as an B<X509> structure, typically causing
195a segmentation violation. If B<x> is set to NULL first then this will not
196happen.
197
198=head1 BUGS
199
200In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when 
201B<*px> is valid is broken and some parts of the reused structure may
202persist if they are not present in the new one. As a result the use
203of this "reuse" behaviour is strongly discouraged.
204
205i2d_X509() will not return an error in many versions of OpenSSL,
206if mandatory fields are not initialized due to a programming error
207then the encoded structure may contain invalid data or omit the
208fields entirely and will not be parsed by d2i_X509(). This may be
209fixed in future so code should not assume that i2d_X509() will
210always succeed.
211
212=head1 RETURN VALUES
213
214d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
215or B<NULL> if an error occurs. The error code that can be obtained by
216L<ERR_get_error(3)|ERR_get_error(3)>. If the "reuse" capability has been used
217with a valid X509 structure being passed in via B<px> then the object is not
218freed in the event of error but may be in a potentially invalid or inconsistent
219state.
220
221i2d_X509() returns the number of bytes successfully encoded or a negative
222value if an error occurs. The error code can be obtained by
223L<ERR_get_error(3)|ERR_get_error(3)>. 
224
225i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error 
226occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 
227
228=head1 SEE ALSO
229
230L<ERR_get_error(3)|ERR_get_error(3)>
231
232=head1 HISTORY
233
234d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
235are available in all versions of SSLeay and OpenSSL.
236
237=cut
238