d2i_X509(3) OpenSSL d2i_X509(3)
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, 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(X509 *x, BIO *bp);
int i2d_X509_fp(X509 *x, FILE *fp);
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 *out. 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 *out 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 sre( 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
OESL_mlo( and the subsequent call to OESL_fe( 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 di_X0(:
X509 *x;
if (!d2i_X509(&x, &p, len))
/* Some error */
This will probably crash somewhere in di_X0(. 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(), i2d_X509_bio() and i2d_X509_fp() return a 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() returns 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.
0.9.7l 2002-11-14 d2i_X509(3)
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