EVP_PKEY_ASN1_METHOD(3ossl)

💅 EVP_PKEY_ASN1_METHOD — the OpenSSL manual page, part 1 💅

okay so bestie, buckle up 🎀 this is EVP_PKEY_ASN1_METHOD(3ossl) and it's literally the page about manipulating and registering the EVP_PKEY_ASN1_METHOD structure. it's giving "backend lore" and honestly? iconic. there's a LOT of names packed in here so let's meet the whole cast first 👑

✨ NAME ✨

say hi to the whole squad, because this page covers all of these babes:

EVP_PKEY_ASN1_METHOD
EVP_PKEY_asn1_new
EVP_PKEY_asn1_copy
EVP_PKEY_asn1_free
EVP_PKEY_asn1_add0
EVP_PKEY_asn1_add_alias
EVP_PKEY_asn1_set_public
EVP_PKEY_asn1_set_private
EVP_PKEY_asn1_set_param
EVP_PKEY_asn1_set_free
EVP_PKEY_asn1_set_ctrl
EVP_PKEY_asn1_set_item
EVP_PKEY_asn1_set_siginf
EVP_PKEY_asn1_set_check
EVP_PKEY_asn1_set_public_check
EVP_PKEY_asn1_set_param_check
EVP_PKEY_asn1_set_security_bits
EVP_PKEY_asn1_set_set_priv_key
EVP_PKEY_asn1_set_set_pub_key
EVP_PKEY_asn1_set_get_priv_key
EVP_PKEY_asn1_set_get_pub_key
EVP_PKEY_get0_asn1

and what's the vibe of the whole group? manipulating and registering EVP_PKEY_ASN1_METHOD structure. that's the assignment. periodt 💅

🌸 SYNOPSIS 🌸

first things first, you gotta pull in the header — no cap, nothing works without it:

#include <openssl/evp.h>

then we got this little typedef, which is lowkey just a struct with a glow-up:

typedef struct evp_pkey_asn1_method_st EVP_PKEY_ASN1_METHOD;

and here's every single function signature, copy-pasted exactly because these are not the vibe to get wrong 😭

EVP_PKEY_ASN1_METHOD *EVP_PKEY_asn1_new(int id, int flags,
                                        const char *pem_str,
                                        const char *info);
void EVP_PKEY_asn1_copy(EVP_PKEY_ASN1_METHOD *dst,
                        const EVP_PKEY_ASN1_METHOD *src);
void EVP_PKEY_asn1_free(EVP_PKEY_ASN1_METHOD *ameth);
int EVP_PKEY_asn1_add0(const EVP_PKEY_ASN1_METHOD *ameth);
int EVP_PKEY_asn1_add_alias(int to, int from);

void EVP_PKEY_asn1_set_public(EVP_PKEY_ASN1_METHOD *ameth,
                              int (*pub_decode) (EVP_PKEY *pk,
                                                 const X509_PUBKEY *pub),
                              int (*pub_encode) (X509_PUBKEY *pub,
                                                 const EVP_PKEY *pk),
                              int (*pub_cmp) (const EVP_PKEY *a,
                                              const EVP_PKEY *b),
                              int (*pub_print) (BIO *out,
                                                const EVP_PKEY *pkey,
                                                int indent, ASN1_PCTX *pctx),
                              int (*pkey_size) (const EVP_PKEY *pk),
                              int (*pkey_bits) (const EVP_PKEY *pk));
void EVP_PKEY_asn1_set_private(EVP_PKEY_ASN1_METHOD *ameth,
                               int (*priv_decode) (EVP_PKEY *pk,
                                                   const PKCS8_PRIV_KEY_INFO
                                                   *p8inf),
                               int (*priv_encode) (PKCS8_PRIV_KEY_INFO *p8,
                                                   const EVP_PKEY *pk),
                               int (*priv_print) (BIO *out,
                                                  const EVP_PKEY *pkey,
                                                  int indent,
                                                  ASN1_PCTX *pctx));
void EVP_PKEY_asn1_set_param(EVP_PKEY_ASN1_METHOD *ameth,
                             int (*param_decode) (EVP_PKEY *pkey,
                                                  const unsigned char **pder,
                                                  int derlen),
                             int (*param_encode) (const EVP_PKEY *pkey,
                                                  unsigned char **pder),
                             int (*param_missing) (const EVP_PKEY *pk),
                             int (*param_copy) (EVP_PKEY *to,
                                                const EVP_PKEY *from),
                             int (*param_cmp) (const EVP_PKEY *a,
                                               const EVP_PKEY *b),
                             int (*param_print) (BIO *out,
                                                 const EVP_PKEY *pkey,
                                                 int indent,
                                                 ASN1_PCTX *pctx));

void EVP_PKEY_asn1_set_free(EVP_PKEY_ASN1_METHOD *ameth,
                            void (*pkey_free) (EVP_PKEY *pkey));
void EVP_PKEY_asn1_set_ctrl(EVP_PKEY_ASN1_METHOD *ameth,
                            int (*pkey_ctrl) (EVP_PKEY *pkey, int op,
                                              long arg1, void *arg2));
void EVP_PKEY_asn1_set_item(EVP_PKEY_ASN1_METHOD *ameth,
                            int (*item_verify) (EVP_MD_CTX *ctx,
                                                const ASN1_ITEM *it,
                                                void *asn,
                                                X509_ALGOR *a,
                                                ASN1_BIT_STRING *sig,
                                                EVP_PKEY *pkey),
                            int (*item_sign) (EVP_MD_CTX *ctx,
                                              const ASN1_ITEM *it,
                                              void *asn,
                                              X509_ALGOR *alg1,
                                              X509_ALGOR *alg2,
                                              ASN1_BIT_STRING *sig));

void EVP_PKEY_asn1_set_siginf(EVP_PKEY_ASN1_METHOD *ameth,
                              int (*siginf_set) (X509_SIG_INFO *siginf,
                                                 const X509_ALGOR *alg,
                                                 const ASN1_STRING *sig));

void EVP_PKEY_asn1_set_check(EVP_PKEY_ASN1_METHOD *ameth,
                             int (*pkey_check) (const EVP_PKEY *pk));

void EVP_PKEY_asn1_set_public_check(EVP_PKEY_ASN1_METHOD *ameth,
                                    int (*pkey_pub_check) (const EVP_PKEY *pk));

void EVP_PKEY_asn1_set_param_check(EVP_PKEY_ASN1_METHOD *ameth,
                                   int (*pkey_param_check) (const EVP_PKEY *pk));

void EVP_PKEY_asn1_set_security_bits(EVP_PKEY_ASN1_METHOD *ameth,
                                     int (*pkey_security_bits) (const EVP_PKEY
                                                                *pk));

void EVP_PKEY_asn1_set_set_priv_key(EVP_PKEY_ASN1_METHOD *ameth,
                                    int (*set_priv_key) (EVP_PKEY *pk,
                                                         const unsigned char
                                                            *priv,
                                                         size_t len));

void EVP_PKEY_asn1_set_set_pub_key(EVP_PKEY_ASN1_METHOD *ameth,
                                   int (*set_pub_key) (EVP_PKEY *pk,
                                                       const unsigned char *pub,
                                                       size_t len));

void EVP_PKEY_asn1_set_get_priv_key(EVP_PKEY_ASN1_METHOD *ameth,
                                    int (*get_priv_key) (const EVP_PKEY *pk,
                                                         unsigned char *priv,
                                                         size_t *len));

void EVP_PKEY_asn1_set_get_pub_key(EVP_PKEY_ASN1_METHOD *ameth,
                                   int (*get_pub_key) (const EVP_PKEY *pk,
                                                       unsigned char *pub,
                                                       size_t *len));

const EVP_PKEY_ASN1_METHOD *EVP_PKEY_get0_asn1(const EVP_PKEY *pkey);

like… look at all those function pointers 🫶 pub_decode, pub_encode, priv_decode, item_verify, set_priv_key, get_pub_key… it's a whole roster of callbacks and honestly they ate. keep this block close, bestie, because everything that comes next is about what all of them actually do 👀

and yeah — that's only part 1. more is coming, so don't go anywhere 🌈

💖 DESCRIPTION 💖

Okay so picture this: EVP_PKEY_ASN1_METHOD is a struct that holds a whole little toolkit of ASN.1 conversion, printing, and info methods for one specific public key algorithm. It's giving "backstage pass for one algorithm" energy.

There are two places where these EVP_PKEY_ASN1_METHOD objects live:

one is a built-in array representing the standard methods for different algorithms 🧚
the other is a stack of user-defined application-specific methods, and you can manipulate that stack with EVP_PKEY_asn1_add0(3) 💅

🛠️ Methods 🛠️

The methods are the underlying implementations of a particular public key algorithm present by the EVP_PKEY object. Yes bestie, this is where the algorithm actually does its thing.

int (*pub_decode) (EVP_PKEY *pk, const X509_PUBKEY *pub);
int (*pub_encode) (X509_PUBKEY *pub, const EVP_PKEY *pk);
int (*pub_cmp) (const EVP_PKEY *a, const EVP_PKEY *b);
int (*pub_print) (BIO *out, const EVP_PKEY *pkey, int indent,
                  ASN1_PCTX *pctx);

pub_decode() and pub_encode() — these are called to decode / encode X509_PUBKEY ASN.1 parameters to / from pk. They MUST return 0 on error, 1 on success. They're called by X509_PUBKEY_get0(3) and X509_PUBKEY_set(3).
pub_cmp() — called when two public keys are compared. It MUST return 1 when the keys are equal, 0 otherwise. It's called by EVP_PKEY_eq(3).
pub_print() — called to print a public key in humanly readable text to out, indented indent spaces. It MUST return 0 on error, 1 on success. It's called by EVP_PKEY_print_public(3).

int (*priv_decode) (EVP_PKEY *pk, const PKCS8_PRIV_KEY_INFO *p8inf);
int (*priv_encode) (PKCS8_PRIV_KEY_INFO *p8, const EVP_PKEY *pk);
int (*priv_print) (BIO *out, const EVP_PKEY *pkey, int indent,
                   ASN1_PCTX *pctx);

priv_decode() and priv_encode() — these decode / encode the PKCS8_PRIV_KEY_INFO form private key to / from pk. They MUST return 0 on error, 1 on success. They're called by EVP_PKCS82PKEY(3) and EVP_PKEY2PKCS8(3).
priv_print() — called to print a private key in humanly readable text to out, indented indent spaces. It MUST return 0 on error, 1 on success. It's called by EVP_PKEY_print_private(3).

int (*pkey_size) (const EVP_PKEY *pk);
int (*pkey_bits) (const EVP_PKEY *pk);
int (*pkey_security_bits) (const EVP_PKEY *pk);

pkey_size() — returns the key size in bytes. It's called by EVP_PKEY_get_size(3).
pkey_bits() — returns the key size in bits. It's called by EVP_PKEY_get_bits(3).
pkey_security_bits() — also part of this trio! The page lists it right here but doesn't give it a separate little blurb, and I'm not out here inventing facts, bestie 🫶

int (*param_decode) (EVP_PKEY *pkey,
                     const unsigned char **pder, int derlen);
int (*param_encode) (const EVP_PKEY *pkey, unsigned char **pder);
int (*param_missing) (const EVP_PKEY *pk);
int (*param_copy) (EVP_PKEY *to, const EVP_PKEY *from);
int (*param_cmp) (const EVP_PKEY *a, const EVP_PKEY *b);
int (*param_print) (BIO *out, const EVP_PKEY *pkey, int indent,
                    ASN1_PCTX *pctx);

param_decode() and param_encode() — these decode / encode DER formatted parameters to / from pk. They MUST return 0 on error, 1 on success. They're called by PEM_read_bio_Parameters(3) and the file: OSSL_STORE_LOADER(3).
param_missing() — returns 0 if a key parameter is missing, otherwise 1. It's called by EVP_PKEY_missing_parameters(3).
param_copy() — copies key parameters from from to to. It MUST return 0 on error, 1 on success. It's called by EVP_PKEY_copy_parameters(3).
param_cmp() — compares the parameters of keys a and b. It MUST return 1 when the keys are equal, 0 when not equal, or a negative number on error. It's called by EVP_PKEY_parameters_eq(3).
param_print() — prints the private key parameters in humanly readable text to out, indented indent spaces. It MUST return 0 on error, 1 on success. It's called by EVP_PKEY_print_params(3).

int (*sig_print) (BIO *out,
                  const X509_ALGOR *sigalg, const ASN1_STRING *sig,
                  int indent, ASN1_PCTX *pctx);

sig_print() — prints a signature in humanly readable text to out, indented indent spaces. sigalg contains the exact signature algorithm. If the signature in sig doesn't correspond to what this method expects, X509_signature_dump() must be used as a last resort. It MUST return 0 on error, 1 on success. It's called by X509_signature_print(3).

void (*pkey_free) (EVP_PKEY *pkey);

pkey_free() — helps freeing the internals of pkey. It's called by EVP_PKEY_free(3), EVP_PKEY_set_type(3), EVP_PKEY_set_type_str(3), and EVP_PKEY_assign(3).

int (*pkey_ctrl) (EVP_PKEY *pkey, int op, long arg1, void *arg2);

pkey_ctrl() — adds extra algorithm specific control. It's called by EVP_PKEY_get_default_digest_nid(3), EVP_PKEY_set1_encoded_public_key(3), EVP_PKEY_get1_encoded_public_key(3), PKCS7_SIGNER_INFO_set(3), PKCS7_RECIP_INFO_set(3), ...

int (*old_priv_decode) (EVP_PKEY *pkey,
                        const unsigned char **pder, int derlen);
int (*old_priv_encode) (const EVP_PKEY *pkey, unsigned char **pder);

old_priv_decode() and old_priv_encode() — these decode / encode the private key pkey from / to a DER formatted array. These are exclusively used to help decoding / encoding older (pre PKCS#8) PEM formatted encrypted private keys. old_priv_decode() MUST return 0 on error, 1 on success. old_priv_encode() MUST return the same kind of values as i2d_PrivateKey(). They're called by d2i_PrivateKey(3) and i2d_PrivateKey(3).

int (*item_verify) (EVP_MD_CTX *ctx, const ASN1_ITEM *it, void *asn,
                    X509_ALGOR *a, ASN1_BIT_STRING *sig, EVP_PKEY *pkey);
int (*item_sign) (EVP_MD_CTX *ctx, const ASN1_ITEM *it, void *asn,
                  X509_ALGOR *alg1, X509_ALGOR *alg2,
                  ASN1_BIT_STRING *sig);

item_sign() and item_verify() — these methods make it possible to have algorithm specific signatures and verification of them. Iconic behavior, honestly.

item_sign() MUST return one of:

<=0 — error
1 — item_sign() did everything, OpenSSL internals just needs to pass the signature length back.
2 — item_sign() did nothing, OpenSSL internal standard routines are expected to continue with the default signature production.
3 — item_sign() set the algorithm identifier algor1 and algor2, OpenSSL internals should just sign using those algorithms.

item_verify() MUST return one of:

<=0 — error
1 — item_sign() did everything, OpenSSL internals just needs to pass the signature length back.
2 — item_sign() did nothing, OpenSSL internal standard routines are expected to continue with the default signature production.

item_verify() and item_sign() are called by ASN1_item_verify(3) and ASN1_item_sign(3), and by extension, X509_verify(3), X509_REQ_verify(3), X509_sign(3), X509_REQ_sign(3), ...

int (*siginf_set) (X509_SIG_INFO *siginf, const X509_ALGOR *alg,
                   const ASN1_STRING *sig);

siginf_set() — used to set custom X509_SIG_INFO parameters. It MUST return 0 on error, or 1 on success. It's called as part of X509_check_purpose(3), X509_check_ca(3) and X509_check_issued(3).

int (*pkey_check) (const EVP_PKEY *pk);
int (*pkey_public_check) (const EVP_PKEY *pk);
int (*pkey_param_check) (const EVP_PKEY *pk);

pkey_check(), pkey_public_check() and pkey_param_check() — used to check the validity of pk for key-pair, public component and parameters, respectively. They MUST return 0 for an invalid key, or 1 for a valid key. They are called by EVP_PKEY_check(3), EVP_PKEY_public_check(3) and EVP_PKEY_param_check(3) respectively.

int (*set_priv_key) (EVP_PKEY *pk, const unsigned char *priv, size_t len);
int (*set_pub_key) (EVP_PKEY *pk, const unsigned char *pub, size_t len);

set_priv_key() and set_pub_key() — used to set the raw private and public key data for an EVP_PKEY. They MUST return 0 on error, or 1 on success. They are called by EVP_PKEY_new_raw_private_key(3), and EVP_PKEY_new_raw_public_key(3) respectively.

size_t (*dirty) (const EVP_PKEY *pk);
void *(*export_to) (const EVP_PKEY *pk, EVP_KEYMGMT *keymgmt);

dirty / dirty_cnt() — the page says dirty_cnt() returns the internal key's dirty count (yep, the member right above is listed as dirty, keeping it exactly as written 👀). This can be used to synchronise different copies of the same keys.
export_to() — exports the key material from the given key to a provider, through the EVP_KEYMGMT(3) interface, if that provider supports importing key material.

✨ Functions ✨

EVP_PKEY_asn1_new() — creates and returns a new EVP_PKEY_ASN1_METHOD object, and associates the given id, flags, pem_str and info. id is a NID, pem_str is the PEM type string, info is a descriptive string. The following flags are supported:
- ASN1_PKEY_SIGPARAM_NULL — if ASN1_PKEY_SIGPARAM_NULL is set, then the signature algorithm parameters are given the type V_ASN1_NULL by default, otherwise they will be given the type V_ASN1_UNDEF (i.e. the parameter is omitted). See X509_ALGOR_set0(3) for more information.
EVP_PKEY_asn1_copy() — copies an EVP_PKEY_ASN1_METHOD object from src to dst. This function is not thread safe, it's recommended to only use this when initializing the application.
EVP_PKEY_asn1_free() — frees an existing EVP_PKEY_ASN1_METHOD pointed by ameth. If the argument is NULL, nothing is done.
EVP_PKEY_asn1_add0() — adds ameth to the user defined stack of methods unless another EVP_PKEY_ASN1_METHOD with the same NID is already there. This function is not thread safe, it's recommended to only use this when initializing the application.
EVP_PKEY_asn1_add_alias() — creates an alias with the NID to for the EVP_PKEY_ASN1_METHOD with NID from unless another EVP_PKEY_ASN1_METHOD with the same NID is already added. This function is not thread safe, it's recommended to only use this when initializing the application.
EVP_PKEY_asn1_set_public(), EVP_PKEY_asn1_set_private(), EVP_PKEY_asn1_set_param(), EVP_PKEY_asn1_set_free(), EVP_PKEY_asn1_set_ctrl(), EVP_PKEY_asn1_set_item(), EVP_PKEY_asn1_set_siginf(), EVP_PKEY_asn1_set_check(), EVP_PKEY_asn1_set_public_check(), EVP_PKEY_asn1_set_param_check(), EVP_PKEY_asn1_set_security_bits(), EVP_PKEY_asn1_set_set_priv_key(), EVP_PKEY_asn1_set_set_pub_key(), EVP_PKEY_asn1_set_get_priv_key() and EVP_PKEY_asn1_set_get_pub_key() — these set the diverse methods of the given EVP_PKEY_ASN1_METHOD object.
EVP_PKEY_get0_asn1() — finds the EVP_PKEY_ASN1_METHOD associated with the key pkey.

🌸 HISTORY 🌸

Okay so bestie, tiny lil' glow-up moment in the history books 📖✨ — the signature of the pub_decode functional argument of EVP_PKEY_asn1_set_public() has changed in OpenSSL 3.0 so its pub parameter is now constified. That's it, that's the lore 🫶 (const-ified, iconic behavior honestly 💅).

💖 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>. 📜💖

Fr fr, read the license before you go doing stuff — it's giving "required reading" energy, no cap 🙈✨

And that's a wrap on this whole page, bestie!! 🎀 You made it to the very end — main character energy fr fr 👑💅. This lil' beauty is from 3.5.0, dated 2026-09-25, and it lives at EVP_PKEY_ASN1_METHOD(3ossl) — go forth and slay those ASN.1 methods 🌈🦋💜

📦 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