ASN1_ITEM_VERIFY(3)

💅 ASN1_ITEM_VERIFY(3) — signature verification for ASN.1 values

okay so bestie, you know how a signature is like a little wax seal that proves something is really from who it says it's from? this page is about the function that does the seal-checking for ASN.1 values, and it's giving very much "trust but verify" energy ✨

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🎀 SYNOPSIS 🎀

it lives in library “libcrypto” and you gotta pull in the header first, no skipping:

#include <openssl/x509.h>

and here's the whole signature (yes, a function about signatures, iconic):

int
ASN1_item_verify(const ASN1_ITEM *it, X509_ALGOR *algor1,
    ASN1_BIT_STRING *sig_in, void *val_in, EVP_PKEY *pkey);

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🦋 DESCRIPTION 🦋

okay so ASN1_item_verify() is literally out here trusting you on one (1) thing: that val_in is an ASN1_VALUE of the type that it says it is. no vibe check on that, it just assumes. 🫶

from there it does the whole routine:

• it encodes that value into DER format by calling ASN1_item_i2d(3)
• then it verifies, in a way similar to EVP_DigestVerify(3), that sig_in contains a valid signature of the resulting byte array

and whose signature is it checking for, you ask? a signature that was created with:

• the signature algorithm algor1, and
• the private key corresponding to the public key pkey

so like, algor1 is the "how", pkey is the "who", and sig_in is the "proof". match made in heaven if everything lines up 💖

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🌸 RETURN VALUES 🌸

the numbers here are doing a lot, so pay attention bestie:

• 1 — signature verification succeeds. slay! 🎉
• 0 — signature verification fails. not slay. 😭
• -1 — something was wrong with the inputs, specifically if:
  • pkey is NULL
  • sig_in contains invalid flags
  • or algor1 requests an invalid or unsupported digest algorithm, or doesn't work with the given pkey

so like, 0 means "the signature is bad" and -1 means "girl, the arguments are bad". different problems, don't mix them up 💀

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🔥 SEE ALSO 🔥

your reading list, go off:

• ASN1_BIT_STRING_new(3)
• ASN1_item_i2d(3)
• ASN1_item_sign(3)
• EVP_DigestVerify(3)
• EVP_PKEY_new(3)
• OBJ_find_sigid_algs(3)
• X509_ALGOR_new(3)

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👑 HISTORY 👑

ASN1_item_verify() first appeared in OpenSSL 0.9.7 and has been available since OpenBSD 3.1. elder icon behavior, honestly ⭐

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and that's the whole page, bestie! this served Debian, June 8, 2025, Library Functions Manual, ASN1_ITEM_VERIFY(3) — go verify something responsibly 🧚💜