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     /xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
     0.9.7e/doc/crypto

     Page 1					    (printed 10/20/05)

     d2i_X509(3)	   14/Nov/2002 (0.9.7e)		   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.

     Page 1					    (printed 10/20/05)

     d2i_X509(3)	   14/Nov/2002 (0.9.7e)		   d2i_X509(3)

	  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;

     Page 2					    (printed 10/20/05)

     d2i_X509(3)	   14/Nov/2002 (0.9.7e)		   d2i_X509(3)

	   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);

     Page 3					    (printed 10/20/05)

     d2i_X509(3)	   14/Nov/2002 (0.9.7e)		   d2i_X509(3)

	   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).

     Page 4					    (printed 10/20/05)

     d2i_X509(3)	   14/Nov/2002 (0.9.7e)		   d2i_X509(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.

     Page 5					    (printed 10/20/05)

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