NAME¶
d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio, i2d_X509_fp - X509
encode and decode functions
SYNOPSIS¶
#include <openssl/x509.h>
X509 *d2i_X509(X509 **px, const unsigned char **in, int len);
int i2d_X509(X509 *x, unsigned char **out);
X509 *d2i_X509_bio(BIO *bp, X509 **x);
X509 *d2i_X509_fp(FILE *fp, X509 **x);
int i2d_X509_bio(BIO *bp, X509 *x);
int i2d_X509_fp(FILE *fp, X509 *x);
DESCRIPTION¶
The X509 encode and decode routines encode and parse an
X509 structure,
which represents an X509 certificate.
d2i_X509() attempts to decode
len bytes at
*in. If
successful a pointer to the
X509 structure is returned. If an error
occurred then
NULL is returned. If
px is not
NULL then
the returned structure is written to
*px. If
*px is not
NULL then it is assumed that
*px contains a valid
X509
structure and an attempt is made to reuse it. If the call is successful
*in is incremented to the byte following the parsed data.
i2d_X509() encodes the structure pointed to by
x into DER format.
If
out is not
NULL is writes the DER encoded data to the buffer
at
*out, and increments it to point after the data just written. If the
return value is negative an error occurred, otherwise it returns the length of
the encoded data.
For OpenSSL 0.9.7 and later if
*out is
NULL memory will be
allocated for a buffer and the encoded data written to it. In this case
*out is not incremented and it points to the start of the data just
written.
d2i_X509_bio() is similar to
d2i_X509() except it attempts to
parse data from BIO
bp.
d2i_X509_fp() is similar to
d2i_X509() except it attempts to parse
data from FILE pointer
fp.
i2d_X509_bio() is similar to
i2d_X509() except it writes the
encoding of the structure
x to BIO
bp and it returns 1 for
success and 0 for failure.
i2d_X509_fp() is similar to
i2d_X509() except it writes the
encoding of the structure
x to BIO
bp and it returns 1 for
success and 0 for failure.
NOTES¶
The letters
i and
d in for example
i2d_X509 stand for
"internal" (that is an internal C structure) and "DER". So
that
i2d_X509 converts from internal to DER.
The functions can also understand
BER forms.
The actual X509 structure passed to
i2d_X509() must be a valid populated
X509 structure it can
not simply be fed with an empty structure
such as that returned by
X509_new().
The encoded data is in binary form and may contain embedded zeroes. Therefore
any FILE pointers or BIOs should be opened in binary mode. Functions such as
strlen() will
not return the correct length
of the encoded structure.
The ways that
*in and
*out are incremented after the operation can
trap the unwary. See the
WARNINGS section for some common errors.
The reason for the auto increment behaviour is to reflect a typical usage of
ASN1 functions: after one structure is encoded or decoded another will
processed after it.
EXAMPLES¶
Allocate and encode the DER encoding of an X509 structure:
int len;
unsigned char *buf, *p;
len = i2d_X509(x, NULL);
buf = OPENSSL_malloc(len);
if (buf == NULL)
/* error */
p = buf;
i2d_X509(x, &p);
If you are using OpenSSL 0.9.7 or later then this can be simplified to:
int len;
unsigned char *buf;
buf = NULL;
len = i2d_X509(x, &buf);
if (len < 0)
/* error */
Attempt to decode a buffer:
X509 *x;
unsigned char *buf, *p;
int len;
/* Something to setup buf and len */
p = buf;
x = d2i_X509(NULL, &p, len);
if (x == NULL)
/* Some error */
Alternative technique:
X509 *x;
unsigned char *buf, *p;
int len;
/* Something to setup buf and len */
p = buf;
x = NULL;
if(!d2i_X509(&x, &p, len))
/* Some error */
WARNINGS¶
The use of temporary variable is mandatory. A common mistake is to attempt to
use a buffer directly as follows:
int len;
unsigned char *buf;
len = i2d_X509(x, NULL);
buf = OPENSSL_malloc(len);
if (buf == NULL)
/* error */
i2d_X509(x, &buf);
/* Other stuff ... */
OPENSSL_free(buf);
This code will result in
buf apparently containing garbage because it was
incremented after the call to point after the data just written. Also
buf will no longer contain the pointer allocated by
OPENSSL_malloc() and the subsequent call to
OPENSSL_free() may well crash.
The auto allocation feature (setting buf to NULL) only works on OpenSSL 0.9.7
and later. Attempts to use it on earlier versions will typically cause a
segmentation violation.
Another trap to avoid is misuse of the
xp argument to
d2i_X509() :
X509 *x;
if (!d2i_X509(&x, &p, len))
/* Some error */
This will probably crash somewhere in
d2i_X509().
The reason for this is that the variable
x is uninitialized and an
attempt will be made to interpret its (invalid) value as an
X509
structure, typically causing a segmentation violation. If
x is set to
NULL first then this will not happen.
BUGS¶
In some versions of OpenSSL the "reuse" behaviour of
d2i_X509()
when
*px is valid is broken and some parts of the reused structure may
persist if they are not present in the new one. As a result the use of this
"reuse" behaviour is strongly discouraged.
i2d_X509() will not return an error in many versions of OpenSSL, if
mandatory fields are not initialized due to a programming error then the
encoded structure may contain invalid data or omit the fields entirely and
will not be parsed by
d2i_X509(). This may be fixed in future so code
should not assume that
i2d_X509() will always succeed.
RETURN VALUES¶
d2i_X509(),
d2i_X509_bio() and
d2i_X509_fp() return a valid
X509 structure or
NULL if an error occurs. The error code that
can be obtained by
ERR_get_error(3).
i2d_X509() returns the number of bytes successfully encoded or a negative
value if an error occurs. The error code can be obtained by
ERR_get_error(3).
i2d_X509_bio() and
i2d_X509_fp() return 1 for success and 0 if an
error occurs The error code can be obtained by
ERR_get_error(3).
SEE ALSO¶
ERR_get_error(3)
HISTORY¶
d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp are
available in all versions of SSLeay and OpenSSL.