/usr/man/cat.3/i2d_X509_bio.3

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, const unsigned char **in, long len);
      X509 *d2i_X509_AUX(X509 **px, const unsigned char **in, long len);
      int i2d_X509(X509 *x, unsigned char **out);
      int i2d_X509_AUX(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);

      int i2d_re_X509_tbs(X509 *x, unsigned char **out);

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. This "reuse"
     capability is present for historical compatibility but its
     use is strongly discouraged (see BUGS below, and the
     discussion in the RETURN VALUES section).

     If the call is successful *in is incremented to the byte
     following the parsed data.

     d2i_X509_AUX() is similar to d2i_X509() but the input is
     expected to consist of an X509 certificate followed by
     auxiliary trust information.  This is used by the PEM
     routines to read "TRUSTED CERTIFICATE" objects.  This
     function should not be called on untrusted input.

     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.

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d2i_X509(3)                  OpenSSL                  d2i_X509(3)

     In this case *out is not incremented and it points to the
     start of the data just written.

     i2d_X509_AUX() is similar to i2d_X509(), but the encoded
     output contains both the certificate and any auxiliary trust
     information.  This is used by the PEM routines to write
     "TRUSTED CERTIFICATE" objects.  Note, this is a non-standard
     OpenSSL-specific data format.

     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.

     i2d_re_X509_tbs() is similar to i2d_X509() except it encodes
     only the TBSCertificate portion of the certificate.

NOTES

     The letters i and d in for example i2d_X509 stand for
     "internal" (that is an internal C structure) and "DER". So
     i2d_X509 converts from internal to DER. The "re" in
     i2d_re_X509_tbs stands for "re-encode", and ensures that a
     fresh encoding is generated in case the object has been
     modified after creation (see the BUGS section).

     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 ssttrrlleenn(()) 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.

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d2i_X509(3)                  OpenSSL                  d2i_X509(3)

     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;

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d2i_X509(3)                  OpenSSL                  d2i_X509(3)

      unsigned char *buf, *p;

      int len;

      /* Something to setup buf and len */

      p = buf;

      x = NULL;

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

     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_mmaalllloocc(()) 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 */

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d2i_X509(3)                  OpenSSL                  d2i_X509(3)

     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 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.

     The encoding of the TBSCertificate portion of a certificate
     is cached in the X509 structure internally to improve
     encoding performance and to ensure certificate signatures
     are verified correctly in some certificates with broken
     (non-DER) encodings.

     Any function which encodes an X509 structure such as
     i2d_X509(), i2d_X509_fp() or i2d_X509_bio() may return a
     stale encoding if the X509 structure has been modified after
     deserialization or previous serialization.

     If, after modification, the X509 object is re-signed with
     X509_sign(), the encoding is automatically renewed.
     Otherwise, the encoding of the TBSCertificate portion of the
     X509 can be manually renewed by calling i2d_re_X509_tbs().

     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). If the "reuse"
     capability has been used with a valid X509 structure being
     passed in via px then the object is not freed in the event
     of error but may be in a potentially invalid or inconsistent
     state.

     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).

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d2i_X509(3)                  OpenSSL                  d2i_X509(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.

1.0.2t               Last change: 2019-09-10                    6

See also d2i_X509(3)
See also d2i_X509_bio(3)
See also d2i_X509_fp(3)
See also i2d_X509(3)
See also i2d_X509_fp(3)