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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 fail‐
       ure.

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 popu‐
       lated 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_mal‐
       loc() 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 per‐
       sist 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 struc‐
       ture 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.

0.9.7d				  2003-11-20			   d2i_X509(3)
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