ASN1_ITEM_D2I_BIO(3ossl)

💅 ASN1_ITEM_D2I_BIO(3ossl) — bestie, let's talk DER

okay so this one is the ASN1_ITEM_D2I_BIO(3ossl) page, which is a whole family of functions that decode and encode DER-encoded ASN.1 structures. Sounds scary, it's not, come sit with me 🫶

✨ NAME ✨

ASN1_item_d2i_ex, ASN1_item_d2i, ASN1_item_d2i_bio_ex, ASN1_item_d2i_bio, ASN1_item_d2i_fp_ex, ASN1_item_d2i_fp, ASN1_item_i2d_mem_bio, ASN1_item_pack, ASN1_item_unpack_ex, ASN1_item_unpack — decoding and encoding DER-encoded ASN.1 structures, the whole girl squad 💖

🌸 SYNOPSIS 🌸

#include <openssl/asn1.h>

ASN1_VALUE *ASN1_item_d2i_ex(ASN1_VALUE **pval, const unsigned char **in,
                             long len, const ASN1_ITEM *it,
                             OSSL_LIB_CTX *libctx, const char *propq);
ASN1_VALUE *ASN1_item_d2i(ASN1_VALUE **pval, const unsigned char **in,
                          long len, const ASN1_ITEM *it);

void *ASN1_item_d2i_bio_ex(const ASN1_ITEM *it, BIO *in, void *x,
                           OSSL_LIB_CTX *libctx, const char *propq);
void *ASN1_item_d2i_bio(const ASN1_ITEM *it, BIO *in, void *x);

void *ASN1_item_d2i_fp_ex(const ASN1_ITEM *it, FILE *in, void *x,
                          OSSL_LIB_CTX *libctx, const char *propq);
void *ASN1_item_d2i_fp(const ASN1_ITEM *it, FILE *in, void *x);

BIO *ASN1_item_i2d_mem_bio(const ASN1_ITEM *it, const ASN1_VALUE *val);

ASN1_STRING *ASN1_item_pack(void *obj, const ASN1_ITEM *it, ASN1_STRING **oct);

void *ASN1_item_unpack(const ASN1_STRING *oct, const ASN1_ITEM *it);

void *ASN1_item_unpack_ex(const ASN1_STRING *oct, const ASN1_ITEM *it,
                         OSSL_LIB_CTX *libctx, const char *propq);

💜 DESCRIPTION 💜

🎀 the `d2i` girlies (decoding)

ASN1_item_d2i_ex() decodes the contents of the data stored in *in of length len, which must be a DER-encoded ASN.1 structure, using the ASN.1 template it. It places the result in *pval unless pval is NULL. If *pval is non-NULL on entry, then the ASN1_VALUE present there gets reused (no cap, recycling is iconic ♻️). Otherwise a brand new ASN1_VALUE gets allocated. If any algorithm fetches are required during the process, they use the OSSL_LIB_CTX provided in the libctx parameter and the property query string in propq. See "ALGORITHM FETCHING" in crypto(7) for more info about algorithm fetching. On exit, *in gets updated to point to the next byte in the buffer after the decoded structure. 👑

ASN1_item_d2i() is the same as ASN1_item_d2i_ex() except that the default OSSL_LIB_CTX is used (i.e. NULL) and with a NULL property query string.

🦋 the BIO + FILE variants

ASN1_item_d2i_bio_ex() decodes the contents of its input BIO in, which must be a DER-encoded ASN.1 structure, using the ASN.1 template it, and places the result in *pval unless pval is NULL. If in is NULL it returns NULL, else a pointer to the parsed structure. If any algorithm fetches are required during the process, they'll use the OSSL_LIB_CTX provided in the libctx parameter and the property query string in propq. See "ALGORITHM FETCHING" in crypto(7) for more info about algorithm fetching.

ASN1_item_d2i_bio() is the same as ASN1_item_d2i_bio_ex() except that the default OSSL_LIB_CTX is used (i.e. NULL) and with a NULL property query string.

ASN1_item_d2i_fp_ex() is the same as ASN1_item_d2i_bio_ex() except that a FILE pointer is provided instead of a BIO.

ASN1_item_d2i_fp() is the same as ASN1_item_d2i_fp_ex() except that the default OSSL_LIB_CTX is used (i.e. NULL) and with a NULL property query string.

🌈 now the encoding side, we love her

ASN1_item_i2d_mem_bio() encodes the given ASN.1 value val using the ASN.1 template it and returns the result in a memory BIO. literally so convenient ✨

ASN1_item_pack() encodes the given ASN.1 value in obj using the ASN.1 template it and returns an ASN1_STRING object. If the passed-in *oct is not NULL, then that gets used to store the returned result, otherwise a new ASN1_STRING object is created. If oct is not NULL and *oct is NULL, then the return value also gets set into *oct.

⚠️ ok important caveat bestie: if there's an error, the optional passed-in ASN1_STRING will not be freed — but the previous value may be cleared when ASN1_STRING_set0(*oct, NULL, 0) is called internally. noted. don't come for me 💀

ASN1_item_unpack() uses ASN1_item_d2i() to decode the DER-encoded ASN1_STRING oct using the ASN.1 template it.

ASN1_item_unpack_ex() is similar to ASN1_item_unpack(), but uses ASN1_item_d2i_ex() so that the libctx and propq can be used when doing algorithm fetching.

🔥 RETURN VALUES 🔥

ASN1_item_d2i_bio(), ASN1_item_unpack_ex() and ASN1_item_unpack() — return a pointer to an ASN1_VALUE, or NULL on error.
ASN1_item_i2d_mem_bio() — returns a pointer to a memory BIO, or NULL on error.
ASN1_item_pack() — returns a pointer to an ASN1_STRING, or NULL on error.

⭐ HISTORY ⭐

The functions ASN1_item_d2i_ex(), ASN1_item_d2i_bio_ex(), ASN1_item_d2i_fp_ex() and ASN1_item_i2d_mem_bio() were added in OpenSSL 3.0.
The function ASN1_item_unpack_ex() was added in OpenSSL 3.2.

👑 COPYRIGHT 👑

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

and that's the whole page bestie, you ate that 💅✨ — this was version 3.5.0, dated 2026-09-25, brought to you by the ASN1_ITEM_D2I_BIO(3ossl) manual. go decode something 🎀

📦 where this page comes from

opensuse-leap 16.0: openssl-3-doc 3.5.0-160000.11.1 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms

ASN1_ITEM_D2I_BIO(3ossl)