5 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio,
6 i2d_X509_fp - X509 encode and decode functions
10 #include <openssl/x509.h>
12 X509 *d2i_X509(X509 **px, const unsigned char **in, int len);
13 int i2d_X509(X509 *x, unsigned char **out);
15 X509 *d2i_X509_bio(BIO *bp, X509 **x);
16 X509 *d2i_X509_fp(FILE *fp, X509 **x);
18 int i2d_X509_bio(BIO *bp, X509 *x);
19 int i2d_X509_fp(FILE *fp, X509 *x);
23 The X509 encode and decode routines encode and parse an
24 B<X509> structure, which represents an X509 certificate.
26 d2i_X509() attempts to decode B<len> bytes at B<*in>. If
27 successful a pointer to the B<X509> structure is returned. If an error
28 occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
29 returned structure is written to B<*px>. If B<*px> is not B<NULL>
30 then it is assumed that B<*px> contains a valid B<X509>
31 structure and an attempt is made to reuse it. This "reuse" capability is present
32 for historical compatibility but its use is B<strongly discouraged> (see BUGS
33 below, and the discussion in the RETURN VALUES section).
35 If the call is successful B<*in> is incremented to the byte following the
38 i2d_X509() encodes the structure pointed to by B<x> into DER format.
39 If B<out> is not B<NULL> is writes the DER encoded data to the buffer
40 at B<*out>, and increments it to point after the data just written.
41 If the return value is negative an error occurred, otherwise it
42 returns the length of the encoded data.
44 For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
45 allocated for a buffer and the encoded data written to it. In this
46 case B<*out> is not incremented and it points to the start of the
49 d2i_X509_bio() is similar to d2i_X509() except it attempts
50 to parse data from BIO B<bp>.
52 d2i_X509_fp() is similar to d2i_X509() except it attempts
53 to parse data from FILE pointer B<fp>.
55 i2d_X509_bio() is similar to i2d_X509() except it writes
56 the encoding of the structure B<x> to BIO B<bp> and it
57 returns 1 for success and 0 for failure.
59 i2d_X509_fp() is similar to i2d_X509() except it writes
60 the encoding of the structure B<x> to BIO B<bp> and it
61 returns 1 for success and 0 for failure.
65 The 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
67 B<i2d_X509> converts from internal to DER.
69 The functions can also understand B<BER> forms.
71 The actual X509 structure passed to i2d_X509() must be a valid
72 populated B<X509> structure it can B<not> simply be fed with an
73 empty structure such as that returned by X509_new().
75 The encoded data is in binary form and may contain embedded zeroes.
76 Therefore any FILE pointers or BIOs should be opened in binary mode.
77 Functions such as B<strlen()> will B<not> return the correct length
78 of the encoded structure.
80 The ways that B<*in> and B<*out> are incremented after the operation
81 can trap the unwary. See the B<WARNINGS> section for some common
84 The reason for the auto increment behaviour is to reflect a typical
85 usage of ASN1 functions: after one structure is encoded or decoded
86 another will processed after it.
90 Allocate and encode the DER encoding of an X509 structure:
93 unsigned char *buf, *p;
95 len = i2d_X509(x, NULL);
97 buf = OPENSSL_malloc(len);
106 If you are using OpenSSL 0.9.7 or later then this can be
115 len = i2d_X509(x, &buf);
120 Attempt to decode a buffer:
124 unsigned char *buf, *p;
128 /* Something to setup buf and len */
132 x = d2i_X509(NULL, &p, len);
137 Alternative technique:
141 unsigned char *buf, *p;
145 /* Something to setup buf and len */
151 if(!d2i_X509(&x, &p, len))
157 The use of temporary variable is mandatory. A common
158 mistake is to attempt to use a buffer directly as follows:
163 len = i2d_X509(x, NULL);
165 buf = OPENSSL_malloc(len);
172 /* Other stuff ... */
176 This code will result in B<buf> apparently containing garbage because
177 it was incremented after the call to point after the data just written.
178 Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
179 and the subsequent call to B<OPENSSL_free()> may well crash.
181 The auto allocation feature (setting buf to NULL) only works on OpenSSL
182 0.9.7 and later. Attempts to use it on earlier versions will typically
183 cause a segmentation violation.
185 Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
189 if (!d2i_X509(&x, &p, len))
192 This will probably crash somewhere in B<d2i_X509()>. The reason for this
193 is that the variable B<x> is uninitialized and an attempt will be made to
194 interpret its (invalid) value as an B<X509> structure, typically causing
195 a segmentation violation. If B<x> is set to NULL first then this will not
200 In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when
201 B<*px> is valid is broken and some parts of the reused structure may
202 persist if they are not present in the new one. As a result the use
203 of this "reuse" behaviour is strongly discouraged.
205 i2d_X509() will not return an error in many versions of OpenSSL,
206 if mandatory fields are not initialized due to a programming error
207 then the encoded structure may contain invalid data or omit the
208 fields entirely and will not be parsed by d2i_X509(). This may be
209 fixed in future so code should not assume that i2d_X509() will
214 d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
215 or B<NULL> if an error occurs. The error code that can be obtained by
216 L<ERR_get_error(3)|ERR_get_error(3)>. If the "reuse" capability has been used
217 with a valid X509 structure being passed in via B<px> then the object is not
218 freed in the event of error but may be in a potentially invalid or inconsistent
221 i2d_X509() returns the number of bytes successfully encoded or a negative
222 value if an error occurs. The error code can be obtained by
223 L<ERR_get_error(3)|ERR_get_error(3)>.
225 i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error
226 occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
230 L<ERR_get_error(3)|ERR_get_error(3)>
234 d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
235 are available in all versions of SSLeay and OpenSSL.