426 lines
11 KiB
Groff
426 lines
11 KiB
Groff
.\" $NetBSD: d2i_X509.3,v 1.4 2005/04/24 00:10:04 wiz Exp $
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.\"
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.\" ========================================================================
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.\"
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.IX Title "d2i_X509 3"
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.TH d2i_X509 3 "2003-07-24" "0.9.7g" "OpenSSL"
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.SH "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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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/x509.h>
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.Ve
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.PP
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.Vb 2
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\& X509 *d2i_X509(X509 **px, unsigned char **in, int len);
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\& int i2d_X509(X509 *x, unsigned char **out);
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.Ve
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.PP
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.Vb 2
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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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.Ve
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.PP
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.Vb 2
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\& int i2d_X509_bio(X509 *x, BIO *bp);
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\& int i2d_X509_fp(X509 *x, FILE *fp);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The X509 encode and decode routines encode and parse an
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\&\fBX509\fR structure, which represents an X509 certificate.
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.PP
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\&\fId2i_X509()\fR attempts to decode \fBlen\fR bytes at \fB*out\fR. If
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successful a pointer to the \fBX509\fR structure is returned. If an error
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occurred then \fB\s-1NULL\s0\fR is returned. If \fBpx\fR is not \fB\s-1NULL\s0\fR then the
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returned structure is written to \fB*px\fR. If \fB*px\fR is not \fB\s-1NULL\s0\fR
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then it is assumed that \fB*px\fR contains a valid \fBX509\fR
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structure and an attempt is made to reuse it. If the call is
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successful \fB*out\fR is incremented to the byte following the
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parsed data.
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.PP
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\&\fIi2d_X509()\fR encodes the structure pointed to by \fBx\fR into \s-1DER\s0 format.
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If \fBout\fR is not \fB\s-1NULL\s0\fR is writes the \s-1DER\s0 encoded data to the buffer
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at \fB*out\fR, 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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.PP
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For OpenSSL 0.9.7 and later if \fB*out\fR is \fB\s-1NULL\s0\fR 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 \fB*out\fR is not incremented and it points to the start of the
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data just written.
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.PP
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\&\fId2i_X509_bio()\fR is similar to \fId2i_X509()\fR except it attempts
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to parse data from \s-1BIO\s0 \fBbp\fR.
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.PP
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\&\fId2i_X509_fp()\fR is similar to \fId2i_X509()\fR except it attempts
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to parse data from \s-1FILE\s0 pointer \fBfp\fR.
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.PP
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\&\fIi2d_X509_bio()\fR is similar to \fIi2d_X509()\fR except it writes
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the encoding of the structure \fBx\fR to \s-1BIO\s0 \fBbp\fR and it
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returns 1 for success and 0 for failure.
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.PP
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\&\fIi2d_X509_fp()\fR is similar to \fIi2d_X509()\fR except it writes
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the encoding of the structure \fBx\fR to \s-1BIO\s0 \fBbp\fR and it
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returns 1 for success and 0 for failure.
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.SH "NOTES"
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.IX Header "NOTES"
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The letters \fBi\fR and \fBd\fR in for example \fBi2d_X509\fR stand for
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\&\*(L"internal\*(R" (that is an internal C structure) and \*(L"\s-1DER\s0\*(R". So that
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\&\fBi2d_X509\fR converts from internal to \s-1DER\s0.
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.PP
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The functions can also understand \fB\s-1BER\s0\fR forms.
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.PP
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The actual X509 structure passed to \fIi2d_X509()\fR must be a valid
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populated \fBX509\fR structure it can \fBnot\fR simply be fed with an
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empty structure such as that returned by \fIX509_new()\fR.
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.PP
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The encoded data is in binary form and may contain embedded zeroes.
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Therefore any \s-1FILE\s0 pointers or BIOs should be opened in binary mode.
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Functions such as \fB\f(BIstrlen()\fB\fR will \fBnot\fR return the correct length
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of the encoded structure.
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.PP
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The ways that \fB*in\fR and \fB*out\fR are incremented after the operation
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can trap the unwary. See the \fB\s-1WARNINGS\s0\fR section for some common
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errors.
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.PP
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The reason for the auto increment behaviour is to reflect a typical
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usage of \s-1ASN1\s0 functions: after one structure is encoded or decoded
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another will processed after it.
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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Allocate and encode the \s-1DER\s0 encoding of an X509 structure:
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.PP
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.Vb 2
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\& int len;
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\& unsigned char *buf, *p;
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.Ve
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.PP
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.Vb 1
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\& len = i2d_X509(x, NULL);
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.Ve
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.PP
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.Vb 1
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\& buf = OPENSSL_malloc(len);
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.Ve
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.PP
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.Vb 2
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\& if (buf == NULL)
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\& /* error */
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.Ve
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.PP
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.Vb 1
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\& p = buf;
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.Ve
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.PP
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.Vb 1
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\& i2d_X509(x, &p);
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.Ve
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.PP
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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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.PP
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.Vb 2
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\& int len;
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\& unsigned char *buf;
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.Ve
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.PP
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.Vb 1
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\& buf = NULL;
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.Ve
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.PP
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.Vb 1
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\& len = i2d_X509(x, &buf);
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.Ve
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.PP
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.Vb 2
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\& if (len < 0)
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\& /* error */
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.Ve
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.PP
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Attempt to decode a buffer:
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.PP
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.Vb 1
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\& X509 *x;
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.Ve
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.PP
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.Vb 1
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\& unsigned char *buf, *p;
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.Ve
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.PP
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.Vb 1
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\& int len;
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.Ve
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.PP
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.Vb 1
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\& /* Something to setup buf and len */
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.Ve
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.PP
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.Vb 1
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\& p = buf;
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.Ve
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.PP
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.Vb 1
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\& x = d2i_X509(NULL, &p, len);
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.Ve
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.PP
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.Vb 2
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\& if (x == NULL)
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\& /* Some error */
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.Ve
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.PP
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Alternative technique:
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.PP
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.Vb 1
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\& X509 *x;
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.Ve
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.PP
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.Vb 1
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\& unsigned char *buf, *p;
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.Ve
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.PP
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.Vb 1
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\& int len;
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.Ve
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.PP
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.Vb 1
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\& /* Something to setup buf and len */
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.Ve
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.PP
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.Vb 1
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\& p = buf;
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.Ve
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.PP
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.Vb 1
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\& x = NULL;
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.Ve
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.PP
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.Vb 2
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\& if(!d2i_X509(&x, &p, len))
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\& /* Some error */
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.Ve
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.SH "WARNINGS"
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.IX Header "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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.PP
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.Vb 2
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\& int len;
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\& unsigned char *buf;
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.Ve
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.PP
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.Vb 1
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\& len = i2d_X509(x, NULL);
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.Ve
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.PP
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.Vb 1
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\& buf = OPENSSL_malloc(len);
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.Ve
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.PP
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.Vb 2
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\& if (buf == NULL)
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\& /* error */
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.Ve
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.PP
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.Vb 1
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\& i2d_X509(x, &buf);
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.Ve
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.PP
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.Vb 1
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\& /* Other stuff ... */
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.Ve
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.PP
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.Vb 1
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\& OPENSSL_free(buf);
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.Ve
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.PP
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This code will result in \fBbuf\fR 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 \fBbuf\fR will no longer contain the pointer allocated by \fB\f(BIOPENSSL_malloc()\fB\fR
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and the subsequent call to \fB\f(BIOPENSSL_free()\fB\fR may well crash.
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.PP
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The auto allocation feature (setting buf to \s-1NULL\s0) 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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.PP
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Another trap to avoid is misuse of the \fBxp\fR argument to \fB\f(BId2i_X509()\fB\fR:
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.PP
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.Vb 1
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\& X509 *x;
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.Ve
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.PP
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.Vb 2
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\& if (!d2i_X509(&x, &p, len))
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\& /* Some error */
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.Ve
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.PP
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This will probably crash somewhere in \fB\f(BId2i_X509()\fB\fR. The reason for this
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is that the variable \fBx\fR is uninitialized and an attempt will be made to
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interpret its (invalid) value as an \fBX509\fR structure, typically causing
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a segmentation violation. If \fBx\fR is set to \s-1NULL\s0 first then this will not
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happen.
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.SH "BUGS"
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.IX Header "BUGS"
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In some versions of OpenSSL the \*(L"reuse\*(R" behaviour of \fId2i_X509()\fR when
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\&\fB*px\fR 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 \*(L"reuse\*(R" behaviour is strongly discouraged.
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.PP
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\&\fIi2d_X509()\fR 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
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fields entirely and will not be parsed by \fId2i_X509()\fR. This may be
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fixed in future so code should not assume that \fIi2d_X509()\fR will
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always succeed.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fId2i_X509()\fR, \fId2i_X509_bio()\fR and \fId2i_X509_fp()\fR return a valid \fBX509\fR structure
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or \fB\s-1NULL\s0\fR if an error occurs. The error code that can be obtained by
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\&\fIERR_get_error\fR\|(3).
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.PP
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\&\fIi2d_X509()\fR, \fIi2d_X509_bio()\fR and \fIi2d_X509_fp()\fR return a the number of bytes
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successfully encoded or a negative value if an error occurs. The error code
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can be obtained by \fIERR_get_error\fR\|(3).
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.PP
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\&\fIi2d_X509_bio()\fR and \fIi2d_X509_fp()\fR returns 1 for success and 0 if an error
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occurs The error code can be obtained by \fIERR_get_error\fR\|(3).
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIERR_get_error\fR\|(3)
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.SH "HISTORY"
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.IX Header "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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