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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, 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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On Apache
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