262 lines
7.7 KiB
Text
262 lines
7.7 KiB
Text
=pod
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=head1 NAME
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d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio,
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i2d_X509_fp - X509 encode and decode functions
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=head1 SYNOPSIS
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#include <openssl/x509.h>
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X509 *d2i_X509(X509 **px, const unsigned char **in, int len);
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int i2d_X509(X509 *x, unsigned char **out);
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X509 *d2i_X509_bio(BIO *bp, X509 **x);
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X509 *d2i_X509_fp(FILE *fp, X509 **x);
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int i2d_X509_bio(BIO *bp, X509 *x);
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int i2d_X509_fp(FILE *fp, X509 *x);
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int i2d_re_X509_tbs(X509 *x, unsigned char **out);
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=head1 DESCRIPTION
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The X509 encode and decode routines encode and parse an
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B<X509> structure, which represents an X509 certificate.
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d2i_X509() attempts to decode B<len> bytes at B<*in>. If
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successful a pointer to the B<X509> structure is returned. If an error
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occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
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returned structure is written to B<*px>. If B<*px> is not B<NULL>
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then it is assumed that B<*px> contains a valid B<X509>
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structure and an attempt is made to reuse it. This "reuse" capability is present
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for historical compatibility but its use is B<strongly discouraged> (see BUGS
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below, and the discussion in the RETURN VALUES section).
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If the call is successful B<*in> is incremented to the byte following the
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parsed data.
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i2d_X509() encodes the structure pointed to by B<x> into DER format.
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If B<out> is not B<NULL> is writes the DER encoded data to the buffer
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at B<*out>, and increments it to point after the data just written.
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If the return value is negative an error occurred, otherwise it
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returns the length of the encoded data.
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For OpenSSL 0.9.7 and later if B<*out> is B<NULL> memory will be
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allocated for a buffer and the encoded data written to it. In this
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case B<*out> is not incremented and it points to the start of the
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data just written.
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d2i_X509_bio() is similar to d2i_X509() except it attempts
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to parse data from BIO B<bp>.
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d2i_X509_fp() is similar to d2i_X509() except it attempts
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to parse data from FILE pointer B<fp>.
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i2d_X509_bio() is similar to i2d_X509() except it writes
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the encoding of the structure B<x> to BIO B<bp> and it
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returns 1 for success and 0 for failure.
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i2d_X509_fp() is similar to i2d_X509() except it writes
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the encoding of the structure B<x> to BIO B<bp> and it
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returns 1 for success and 0 for failure.
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i2d_re_X509_tbs() is similar to i2d_X509() except it encodes
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only the TBSCertificate portion of the certificate.
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=head1 NOTES
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The letters B<i> and B<d> in for example B<i2d_X509> stand for
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"internal" (that is an internal C structure) and "DER". So
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B<i2d_X509> converts from internal to DER. The "re" in
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B<i2d_re_X509_tbs> stands for "re-encode", and ensures that a fresh
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encoding is generated in case the object has been modified after
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creation (see the BUGS section).
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The functions can also understand B<BER> forms.
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The actual X509 structure passed to i2d_X509() must be a valid
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populated B<X509> structure it can B<not> simply be fed with an
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empty structure such as that returned by X509_new().
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The encoded data is in binary form and may contain embedded zeroes.
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Therefore any FILE pointers or BIOs should be opened in binary mode.
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Functions such as B<strlen()> will B<not> return the correct length
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of the encoded structure.
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The ways that B<*in> and B<*out> are incremented after the operation
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can trap the unwary. See the B<WARNINGS> section for some common
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errors.
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The reason for the auto increment behaviour is to reflect a typical
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usage of ASN1 functions: after one structure is encoded or decoded if (a != NULL)
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(*a) = ret;
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another will processed after it.
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=head1 EXAMPLES
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Allocate and encode the DER encoding of an X509 structure:
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int len;
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unsigned char *buf, *p;
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len = i2d_X509(x, NULL);
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buf = OPENSSL_malloc(len);
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if (buf == NULL)
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/* error */
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p = buf;
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i2d_X509(x, &p);
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If you are using OpenSSL 0.9.7 or later then this can be
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simplified to:
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int len;
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unsigned char *buf;
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buf = NULL;
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len = i2d_X509(x, &buf);
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if (len < 0)
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/* error */
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Attempt to decode a buffer:
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X509 *x;
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unsigned char *buf, *p;
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int len;
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/* Something to setup buf and len */
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p = buf;
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x = d2i_X509(NULL, &p, len);
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if (x == NULL)
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/* Some error */
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Alternative technique:
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X509 *x;
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unsigned char *buf, *p;
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int len;
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/* Something to setup buf and len */
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p = buf;
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x = NULL;
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if(!d2i_X509(&x, &p, len))
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/* Some error */
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=head1 WARNINGS
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The use of temporary variable is mandatory. A common
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mistake is to attempt to use a buffer directly as follows:
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int len;
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unsigned char *buf;
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len = i2d_X509(x, NULL);
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buf = OPENSSL_malloc(len);
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if (buf == NULL)
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/* error */
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i2d_X509(x, &buf);
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/* Other stuff ... */
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OPENSSL_free(buf);
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This code will result in B<buf> apparently containing garbage because
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it was incremented after the call to point after the data just written.
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Also B<buf> will no longer contain the pointer allocated by B<OPENSSL_malloc()>
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and the subsequent call to B<OPENSSL_free()> may well crash.
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The auto allocation feature (setting buf to NULL) only works on OpenSSL
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0.9.7 and later. Attempts to use it on earlier versions will typically
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cause a segmentation violation.
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Another trap to avoid is misuse of the B<xp> argument to B<d2i_X509()>:
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X509 *x;
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if (!d2i_X509(&x, &p, len))
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/* Some error */
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This will probably crash somewhere in B<d2i_X509()>. The reason for this
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is that the variable B<x> is uninitialized and an attempt will be made to
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interpret its (invalid) value as an B<X509> structure, typically causing
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a segmentation violation. If B<x> is set to NULL first then this will not
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happen.
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=head1 BUGS
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In some versions of OpenSSL the "reuse" behaviour of d2i_X509() when
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B<*px> is valid is broken and some parts of the reused structure may
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persist if they are not present in the new one. As a result the use
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of this "reuse" behaviour is strongly discouraged.
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i2d_X509() will not return an error in many versions of OpenSSL,
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if mandatory fields are not initialized due to a programming error
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then the encoded structure may contain invalid data or omit the if (a != NULL)
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(*a) = ret;
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fields entirely and will not be parsed by d2i_X509(). This may be
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fixed in future so code should not assume that i2d_X509() will
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always succeed.
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The encoding of the TBSCertificate portion of a certificate is cached
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in the B<X509> structure internally to improve encoding performance
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and to ensure certificate signatures are verified correctly in some
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certificates with broken (non-DER) encodings.
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Any function which encodes an X509 structure such as i2d_X509(),
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i2d_X509_fp() or i2d_X509_bio() may return a stale encoding if the
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B<X509> structure has been modified after deserialization or previous
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serialization.
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If, after modification, the B<X509> object is re-signed with X509_sign(),
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the encoding is automatically renewed. Otherwise, the encoding of the
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TBSCertificate portion of the B<X509> can be manually renewed by calling
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i2d_re_X509_tbs().
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=head1 RETURN VALUES
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d2i_X509(), d2i_X509_bio() and d2i_X509_fp() return a valid B<X509> structure
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or B<NULL> if an error occurs. The error code that can be obtained by
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L<ERR_get_error(3)|ERR_get_error(3)>. If the "reuse" capability has been used
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with a valid X509 structure being passed in via B<px> then the object is not
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freed in the event of error but may be in a potentially invalid or inconsistent
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state.
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i2d_X509() returns the number of bytes successfully encoded or a negative
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value if an error occurs. The error code can be obtained by
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L<ERR_get_error(3)|ERR_get_error(3)>.
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i2d_X509_bio() and i2d_X509_fp() return 1 for success and 0 if an error
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occurs The error code can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
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=head1 SEE ALSO
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L<ERR_get_error(3)|ERR_get_error(3)>
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=head1 HISTORY
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d2i_X509, i2d_X509, d2i_X509_bio, d2i_X509_fp, i2d_X509_bio and i2d_X509_fp
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are available in all versions of SSLeay and OpenSSL.
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=cut
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