D2I_ASN1_NULL(3) | Library Functions Manual | D2I_ASN1_NULL(3)

# NAME

`d2i_ASN1_NULL`, `i2d_ASN1_NULL` — decode and encode an ASN.1 NULL type

# SYNOPSIS

library “libcrypto”
`#include <openssl/asn1.h>`

ASN1_NULL *
`d2i_ASN1_NULL`(ASN1_NULL **val_out, const unsigned char **der_in, long length);

int
`i2d_ASN1_NULL`(ASN1_NULL *val_in, unsigned char **der_out);

# DESCRIPTION

These functions decode and encode the ASN.1 value NULL of type NULL. For details about the semantics, examples, caveats, and bugs, see ASN1_item_d2i(3).

`d2i_ASN1_NULL`() verifies that the BER-encoded value at *der_in is NULL and of type NULL. It fails if length is less than 2 or if the first two bytes of *der_in differ from 0x05 and 0x00. In case of success, *der_in is advanced by two bytes and *val_out is set to a specific invalid pointer representing the unique ASN1_NULL object.

`i2d_ASN1_NULL`() ignores val_in and encodes the ASN.1 value NULL of type NULL using DER. Specifically, it writes the identifier octet for the type NULL, 0x05, followed by the length octet 0x00, and no content or end-of-content octets.

# RETURN VALUES

`d2i_ASN1_NULL`() returns a specific invalid pointer representing the unique ASN1_NULL object or `NULL` if an error occurs.

`i2d_ASN1_NULL`() returns 2 if successful or 0 if an error occurs.

# SEE ALSO

ASN1_item_d2i(3), ASN1_item_new(3), ASN1_NULL_new(3), ASN1_TYPE_get(3)

# STANDARDS

ITU-T Recommendation X.690, also known as ISO/IEC 8825-1: Information technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER), section 8.8: Encoding of a null value

# HISTORY

`d2i_ASN1_NULL`() and `i2d_ASN1_NULL`() first appeared in OpenSSL 0.9.5 and have been available since OpenBSD 2.7.

June 8, 2025 | Debian