D2I_X509(3) | Library Functions Manual | D2I_X509(3)

# NAME

`d2i_X509`, `i2d_X509`, `d2i_X509_bio`, `d2i_X509_fp`, `i2d_X509_bio`, `i2d_X509_fp`, `d2i_X509_AUX`, `i2d_X509_AUX`, `d2i_X509_CERT_AUX`, `i2d_X509_CERT_AUX`, `d2i_X509_CINF`, `i2d_X509_CINF`, `d2i_X509_VAL`, `i2d_X509_VAL`, `i2d_re_X509_tbs`, `i2d_re_X509_CRL_tbs`, `i2d_re_X509_REQ_tbs` — decode and encode X.509 certificates

# SYNOPSIS

library “libcrypto”
`#include <openssl/x509.h>`

X509 *
`d2i_X509`(X509 **val_out, const unsigned char **der_in, long length);

int
`i2d_X509`(X509 *val_in, unsigned char **der_out);

X509 *
`d2i_X509_bio`(BIO *in_bio, X509 **val_out);

X509 *
`d2i_X509_fp`(FILE *in_fp, X509 **val_out);

int
`i2d_X509_bio`(BIO *out_bio, X509 *val_in);

int
`i2d_X509_fp`(FILE *out_fp, X509 *val_in);

X509 *
`d2i_X509_AUX`(X509 **val_out, const unsigned char **der_in, long length);

int
`i2d_X509_AUX`(X509 *val_in, unsigned char **der_out);

X509_CERT_AUX *
`d2i_X509_CERT_AUX`(X509_CERT_AUX **val_out, const unsigned char **der_in, long length);

int
`i2d_X509_CERT_AUX`(X509_CERT_AUX *val_in, unsigned char **der_out);

X509_CINF *
`d2i_X509_CINF`(X509_CINF **val_out, const unsigned char **der_in, long length);

int
`i2d_X509_CINF`(X509_CINF *val_in, unsigned char **der_out);

X509_VAL *
`d2i_X509_VAL`(X509_VAL **val_out, const unsigned char **der_in, long length);

int
`i2d_X509_VAL`(X509_VAL *val_in, unsigned char **der_out);

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

int
`i2d_re_X509_CRL_tbs`(X509_CRL *crl, unsigned char **pp);

int
`i2d_re_X509_REQ_tbs`(X509_REQ *req, unsigned char **pp);

# DESCRIPTION

These functions decode and encode X.509 certificates and some of their substructures. For details about the semantics, examples, caveats, and bugs, see ASN1_item_d2i(3).

`d2i_X509`() and `i2d_X509`() decode and encode an ASN.1 Certificate structure defined in RFC 5280 section 4.1.

`d2i_X509_bio`(), `d2i_X509_fp`(), `i2d_X509_bio`(), and `i2d_X509_fp`() are similar except that they decode or encode using a BIO or FILE pointer.

`d2i_X509_AUX`() is similar to `d2i_X509`(), but the input is expected to consist of an X.509 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_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 that this is a non-standard OpenSSL-specific data format.

`d2i_X509_CERT_AUX`() and `i2d_X509_CERT_AUX`() decode and encode optional non-standard auxiliary data appended to a certificate, for example friendly alias names and trust data.

`d2i_X509_CINF`() and `i2d_X509_CINF`() decode and encode an ASN.1 TBSCertificate structure defined in RFC 5280 section 4.1.

`d2i_X509_VAL`() and `i2d_X509_VAL`() decode and encode an ASN.1 Validity structure defined in RFC 5280 section 4.1.

`i2d_re_X509_tbs`() is similar to `i2d_X509`(), except it encodes only the TBSCertificate portion of the certificate. `i2d_re_X509_CRL_tbs`() and `i2d_re_X509_REQ_tbs`() are analogous for CRL and certificate request, respectively. 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.

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.

If, after modification, the X509 object is re-signed with X509_sign(3), 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`(), `d2i_X509_fp`(), and `d2i_X509_AUX`() return a valid X509 structure or `NULL` if an error occurs.

`d2i_X509_CERT_AUX`(), `d2i_X509_CINF`(), and `d2i_X509_VAL`() return an X509_CERT_AUX, X509_CINF, or X509_VAL object, respectively, or `NULL` if an error occurs.

`i2d_X509`(), `i2d_X509_AUX`(), `i2d_X509_CERT_AUX`(), `i2d_X509_CINF`(), and `i2d_X509_VAL`() return the number of bytes successfully encoded or a negative value if an error occurs.

`i2d_X509_bio`() and `i2d_X509_fp`() return 1 for success or 0 if an error occurs.

`i2d_re_X509_tbs`(), `i2d_re_X509_CRL_tbs`(), and `i2d_re_X509_REQ_tbs`() return the number of bytes successfully encoded or 0 if an error occurs.

For all functions, the error code can be obtained by ERR_get_error(3).

# SEE ALSO

ASN1_item_d2i(3), X509_CINF_new(3), X509_new(3)

# STANDARDS

RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

# HISTORY

`d2i_X509`(), `i2d_X509`(), `d2i_X509_fp`(), `i2d_X509_fp`(), `d2i_X509_CINF`(), `i2d_X509_CINF`(), `d2i_X509_VAL`(), and `i2d_X509_VAL`() first appeared in SSLeay 0.5.1. `d2i_X509_bio`() and `i2d_X509_bio`() first appeared in SSLeay 0.6.0. These functions have been available since OpenBSD 2.4.

`d2i_X509_AUX`(), `i2d_X509_AUX`(), `d2i_X509_CERT_AUX`(), and `i2d_X509_CERT_AUX`() first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7.

`i2d_re_X509_tbs`(), `i2d_re_X509_CRL_tbs`(), and `i2d_re_X509_REQ_tbs`() first appeared in OpenSSL 1.1.0 and have been available since OpenBSD 7.1.

June 8, 2025 | Debian