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. 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 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_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.
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().
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). 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).
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.
1.0.2k 2017-01-26 d2i_X509(3)
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