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(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 *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 suc-
       cessful *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 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 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:
           /* 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 OOPPEENNSSSSLL_mmaall--
       lloocc(()) and the subsequent call to OOPPEENNSSSSLL_ffrreeee(()) 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 dd22ii_XX550099(()):

        X509 *x;

        if (!d2i_X509(&x, &p, len))
               /* Some error */

       This will probably crash somewhere in dd22ii_XX550099(()). 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.

       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
       error occurs The error code can be obtained by ERR_get_error(3).

       ERR_get_error(3)

       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.



0.9.8d                            2005-07-13                       d2i_X509(3)