ASN1_ITEM_PACK(3)

📦 version 4.4.0, in alpine 3.24, arch rolling

💜 ASN1_ITEM_PACK(3) — the libcrypto glow-up for your ASN.1 objects

okay so this page lives in section 3 of the manual, bestie — it's ASN1_ITEM_PACK(3), a Library Functions Manual situation, and it's all about squishing an ASN.1 object into an ASN1_STRING and then getting it back out again. two little functions, one very important job. let's go ✨

🌸 NAME 🌸

ASN1_item_pack, ASN1_item_unpack — pack an ASN.1 object into an ASN1_STRING

like, that's literally the whole thing. pack it up, unpack it back. iconic behavior honestly 🎀

🦋 SYNOPSIS 🦋

the library is “libcrypto” and you're gonna want this include, no cap:

#include <openssl/asn1.h>

here are the two function signatures, exactly, character for character, because we do not mess with the code 💅

ASN1_STRING *
ASN1_item_pack(void *val_in, const ASN1_ITEM *it,
    ASN1_STRING **string_out);

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

🧚 DESCRIPTION 🧚

🍓 ASN1_item_pack()

so ASN1_item_pack() takes the object that val_in points to and encodes it into DER format — it does that using ASN1_item_i2d(3), which is doing the actual heavy lifting behind the scenes — and then it stores the encoded form in **string_out. ✨

and here's the cute part: if string_out or *string_out is a NULL pointer, a brand-new ASN1_STRING object gets allocated and returned to you. main character energy — it makes its own container. 🫶

🌈 ASN1_item_unpack()

meanwhile ASN1_item_unpack() looks at the data inside string_in, treats it as a DER- or BER-encoded byte array, and decodes one value of the type into a freshly allocated object using ASN1_item_d2i(3). new object, who dis 😭

notice the vibe check here: packing always produces DER, but unpacking is chill and accepts either DER or BER. iykyk.

👑 RETURN VALUES 👑

  • ASN1_item_pack() — returns the modified or new object, or NULL if memory allocation or encoding fails. 💀
  • ASN1_item_unpack() — returns the new object, or NULL if memory allocation or decoding fails. 🙈

so like... if you get NULL back, something went wrong. don't ignore it, bestie.

💖 SEE ALSO 💖

go read these next, they're the friend group:

⭐ HISTORY ⭐

ASN1_item_pack() and ASN1_item_unpack() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2. og functions fr fr 🧚‍♀️

🎀 BUGS 🎀

not me having to point you at another page for the drama 😭 — see the BUGS section in ASN1_item_i2d(3). that's where the tea is.

and that's the whole page, bestie — slay, you now understand ASN1_item_pack(3) 🦋💅

this one's from the Debian build, dated June 8, 2025 — mwah, catch you in the next manpage 💜✨

📦 where this page comes from