PROVIDER-ASYM_CIPHER(7ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

💅 provider-asym_cipher(7ossl) 💅

okay so bestie, welcome to provider-asym_cipher(7ossl). this page is literally the manual for the asym_cipher library <-> provider functions, and we are keeping every signature exactly as it appears. no skipping, no paraphrasing the code, periodt.

✨ NAME ✨

provider-asym_cipher - The asym_cipher library <-> provider functions.

🦋 SYNOPSIS 🦋

first up, the includes — bestie, these are exact:

#include <openssl/core_dispatch.h>
#include <openssl/core_names.h>

then there’s this iconic comment, and it matters: none of these are actual functions, but they’re displayed like this for the function signatures for functions that are offered as function pointers in OSSL_DISPATCH arrays. so here’s the whole lineup, verbatim:

/*
 * None of these are actual functions, but are displayed like this for
 * the function signatures for functions that are offered as function
 * pointers in OSSL_DISPATCH arrays.
 */

/* Context management */
void *OSSL_FUNC_asym_cipher_newctx(void *provctx);
void OSSL_FUNC_asym_cipher_freectx(void *ctx);
void *OSSL_FUNC_asym_cipher_dupctx(void *ctx);

/* Encryption */
int OSSL_FUNC_asym_cipher_encrypt_init(void *ctx, void *provkey,
                                       const OSSL_PARAM params[]);
int OSSL_FUNC_asym_cipher_encrypt(void *ctx, unsigned char *out, size_t *outlen,
                                  size_t outsize, const unsigned char *in,
                                  size_t inlen);

/* Decryption */
int OSSL_FUNC_asym_cipher_decrypt_init(void *ctx, void *provkey,
                                       const OSSL_PARAM params[]);
int OSSL_FUNC_asym_cipher_decrypt(void *ctx, unsigned char *out, size_t *outlen,
                                  size_t outsize, const unsigned char *in,
                                  size_t inlen);

/* Asymmetric Cipher parameters */
int OSSL_FUNC_asym_cipher_get_ctx_params(void *ctx, OSSL_PARAM params[]);
const OSSL_PARAM *OSSL_FUNC_asym_cipher_gettable_ctx_params(void *provctx);
int OSSL_FUNC_asym_cipher_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
const OSSL_PARAM *OSSL_FUNC_asym_cipher_settable_ctx_params(void *provctx);

🌸 DESCRIPTION 🌸

Okay bestie, real talk: this whole page is mostly for provider authors — the people writing the actual crypto guts. If that's not you, go peek at provider(7) first for the bigger picture 💖

The asymmetric cipher operation, aka OSSL_OP_ASYM_CIPHER, is what lets providers implement asymmetric cipher algorithms and hand them over to applications through the API functions EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3), and the rest of that friend group ✨

Every "function" we talk about here is literally just a function pointer that travels between libcrypto and the provider inside OSSL_DISPATCH(3) arrays, which in turn live in OSSL_ALGORITHM(3) arrays, which get returned by the provider's provider_query_operation() function (see "Provider Functions" in provider-base(7)). It's giving delivery-chain realness 📦

Each of these "functions" has a matching function type definition named OSSL_FUNC_{name}_fn, plus a lil helper function to pull the function pointer out of an OSSL_DISPATCH(3) element, named OSSL_FUNC_{name}. Exhibit A, the "function" OSSL_FUNC_asym_cipher_newctx():

typedef void *(OSSL_FUNC_asym_cipher_newctx_fn)(void *provctx);
static ossl_inline OSSL_FUNC_asym_cipher_newctx_fn
    OSSL_FUNC_asym_cipher_newctx(const OSSL_DISPATCH *opf);

OSSL_DISPATCH(3) arrays are indexed by numbers, and those numbers are provided as macros in openssl-core_dispatch.h(7). Here's the whole lineup, no cap 👑

OSSL_FUNC_asym_cipher_newctx               OSSL_FUNC_ASYM_CIPHER_NEWCTX
OSSL_FUNC_asym_cipher_freectx              OSSL_FUNC_ASYM_CIPHER_FREECTX
OSSL_FUNC_asym_cipher_dupctx               OSSL_FUNC_ASYM_CIPHER_DUPCTX

OSSL_FUNC_asym_cipher_encrypt_init         OSSL_FUNC_ASYM_CIPHER_ENCRYPT_INIT
OSSL_FUNC_asym_cipher_encrypt              OSSL_FUNC_ASYM_CIPHER_ENCRYPT

OSSL_FUNC_asym_cipher_decrypt_init         OSSL_FUNC_ASYM_CIPHER_DECRYPT_INIT
OSSL_FUNC_asym_cipher_decrypt              OSSL_FUNC_ASYM_CIPHER_DECRYPT

OSSL_FUNC_asym_cipher_get_ctx_params       OSSL_FUNC_ASYM_CIPHER_GET_CTX_PARAMS
OSSL_FUNC_asym_cipher_gettable_ctx_params  OSSL_FUNC_ASYM_CIPHER_GETTABLE_CTX_PARAMS
OSSL_FUNC_asym_cipher_set_ctx_params       OSSL_FUNC_ASYM_CIPHER_SET_CTX_PARAMS
OSSL_FUNC_asym_cipher_settable_ctx_params  OSSL_FUNC_ASYM_CIPHER_SETTABLE_CTX_PARAMS

Now, an asymmetric cipher algorithm implementation doesn't have to implement all of these — but there are rules, bestie, and the vibe check is strict 🚨 In order to be a consistent set of functions, a provider must implement OSSL_FUNC_asym_cipher_newctx and OSSL_FUNC_asym_cipher_freectx. It must also implement both of OSSL_FUNC_asym_cipher_encrypt_init and OSSL_FUNC_asym_cipher_encrypt, or both of OSSL_FUNC_asym_cipher_decrypt_init and OSSL_FUNC_asym_cipher_decrypt. Like, pick a lane, but commit to it 💅

OSSL_FUNC_asym_cipher_get_ctx_params is optional — but if it shows up, then OSSL_FUNC_asym_cipher_gettable_ctx_params has to be there too. Same energy for OSSL_FUNC_asym_cipher_set_ctx_params: optional, but if it's present then so must OSSL_FUNC_asym_cipher_settable_ctx_params. They're a package deal, iykyk 🫶

One more thing: an asymmetric cipher algorithm must also implement some mechanism for generating, loading or importing keys via the key management (OSSL_OP_KEYMGMT) operation. See provider-keymgmt(7) for the deets 🔑

🎀 Context Management Functions 🎀

  • OSSL_FUNC_asym_cipher_newctx() — should create and return a pointer to a provider side structure that holds context information during an asymmetric cipher operation. A pointer to this context gets passed back in a bunch of the other asymmetric cipher operation function calls. The parameter provctx is the provider context generated during provider initialisation (see provider(7)). It's the birth of a context, iconic ✨
  • OSSL_FUNC_asym_cipher_freectx() — gets passed a pointer to the provider side asymmetric cipher context in the ctx parameter. This function should free any resources associated with that context. Cleanup era 🧹
  • OSSL_FUNC_asym_cipher_dupctx() — should duplicate the provider side asymmetric cipher context in the ctx parameter and return the duplicate copy. Two contexts, same fit 🦋

🔥 Encryption Functions 🔥

OSSL_FUNC_asym_cipher_encrypt_init() initialises a context for an asymmetric encryption, given a provider side asymmetric cipher context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_asym_cipher_set_ctx_params(). That key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)) — no fresh-out-of-nowhere keys allowed 💀

OSSL_FUNC_asym_cipher_encrypt() performs the actual encryption itself, the main character moment 🫶 A previously initialised asymmetric cipher context is passed in the ctx parameter. The data to be encrypted is pointed to by the in parameter, which is inlen bytes long. Unless out is NULL, the encrypted data should be written to the location pointed to by the out parameter and it should not exceed outsize bytes in length. The length of the encrypted data should be written to *outlen. And if out is NULL, then the maximum length of the encrypted data should be written to *outlen. So literally: out NULL means "just tell me how much room I need" 📏

💜 Decryption Functions 💜

OSSL_FUNC_asym_cipher_decrypt_init() initialises a context for an asymmetric decryption, given a provider side asymmetric cipher context in the ctx parameter and a pointer to a provider key object in the provkey parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_asym_cipher_set_ctx_params(). The key object should have been previously generated, loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)). Same rules, opposite direction 🔄

OSSL_FUNC_asym_cipher_decrypt() performs the actual decryption itself. A previously initialised asymmetric cipher context is passed in the ctx parameter. The data to be decrypted is pointed to by the in parameter, which is inlen bytes long. Unless out is NULL, the decrypted data should be written to the location pointed to by the out parameter and it should not exceed outsize bytes in length. The length of the decrypted data should be written to *outlen. And if out is NULL, then the maximum length of the decrypted data should be written to *outlen. Same *outlen dance, no notes 💃

🦋 Asymmetric Cipher Parameters 🦋

Check out OSSL_PARAM(3) for the full scoop on the parameters structure that OSSL_FUNC_asym_cipher_get_ctx_params() and OSSL_FUNC_asym_cipher_set_ctx_params() roll with.

  • OSSL_FUNC_asym_cipher_get_ctx_params() — gets asymmetric cipher parameters associated with the given provider side asymmetric cipher context ctx and stores them in params. Passing NULL for params should return true. Lowkey a vibe check on its own ✨
  • OSSL_FUNC_asym_cipher_set_ctx_params() — sets the asymmetric cipher parameters associated with the given provider side asymmetric cipher context ctx to params. Any parameter settings are additional to any that were previously set — it adds, it does not replace, bestie. Passing NULL for params should return true 🎀

Parameters currently recognised by built-in asymmetric cipher algorithms are as follows. Heads up though: not all parameters are relevant to, or are understood by, all asymmetric cipher algorithms. Read the room 👀

  • "pad-mode" (OSSL_ASYM_CIPHER_PARAM_PAD_MODE) <UTF8 string> OR <integer> — the type of padding to be used. The interpretation of this value will depend on the algorithm in use. Mysterious, adaptable, we love her 💅
  • "digest" (OSSL_ASYM_CIPHER_PARAM_OAEP_DIGEST) <UTF8 string> — gets or sets the name of the OAEP digest algorithm used when OAEP padding is in use.
  • "digest" (OSSL_ASYM_CIPHER_PARAM_DIGEST) <UTF8 string> — gets or sets the name of the digest algorithm used by the algorithm (where applicable).
  • "digest-props" (OSSL_ASYM_CIPHER_PARAM_OAEP_DIGEST_PROPS) <UTF8 string> — gets or sets the properties to use when fetching the OAEP digest algorithm.
  • "digest-props" (OSSL_ASYM_CIPHER_PARAM_DIGEST_PROPS) <UTF8 string> — gets or sets the properties to use when fetching the cipher digest algorithm.
  • "mgf1-digest" (OSSL_ASYM_CIPHER_PARAM_MGF1_DIGEST) <UTF8 string> — gets or sets the name of the MGF1 digest algorithm used when OAEP or PSS padding is in use.
  • "mgf1-digest-props" (OSSL_ASYM_CIPHER_PARAM_MGF1_DIGEST_PROPS) <UTF8 string> — gets or sets the properties to use when fetching the MGF1 digest algorithm.
  • "oaep-label" (OSSL_ASYM_CIPHER_PARAM_OAEP_LABEL) <octet string ptr> — gets the OAEP label used when OAEP padding is in use.
  • "oaep-label" (OSSL_ASYM_CIPHER_PARAM_OAEP_LABEL) <octet string> — sets the OAEP label used when OAEP padding is in use. Yes, same name twice, one gets and one sets — that's just how it is 🫠
  • "tls-client-version" (OSSL_ASYM_CIPHER_PARAM_TLS_CLIENT_VERSION) <unsigned integer> — the TLS protocol version first requested by the client.
  • "tls-negotiated-version" (OSSL_ASYM_CIPHER_PARAM_TLS_CLIENT_VERSION) <unsigned integer> — the negotiated TLS protocol version. (Yep, it's literally the same macro string up there in the docs — copying it exactly, don't come for me 🙈)
  • "implicit-rejection" (OSSL_ASYM_CIPHER_PARAM_IMPLICIT_REJECTION) <unsigned integer> — gets or sets the use of the implicit rejection mechanism for RSA PKCS#1 v1.5 decryption. When set (non zero value), the decryption API will return a deterministically random value if the PKCS#1 v1.5 padding check fails. This makes exploitation of the Bleichenbacher significantly harder, even if the code using the RSA decryption API is not implemented in side-channel free manner. Set by default in OpenSSL providers. This one's a genuine hero, honestly 👑
Ngl, "implicit-rejection" is doing serious heavy lifting for security. Set by default in OpenSSL providers, and that's a slay for everyone.

The OpenSSL FIPS provider also supports the following parameters:

  • "fips-indicator" (OSSL_ASYM_CIPHER_PARAM_FIPS_APPROVED_INDICATOR) <integer> — a getter that returns 1 if the operation is FIPS approved, or 0 otherwise. This may be used after calling either OSSL_FUNC_asym_cipher_encrypt() or OSSL_FUNC_asym_cipher_decrypt(). It may return 0 if "key-check" is set to 0.
  • "key-check" (OSSL_ASYM_CIPHER_PARAM_FIPS_KEY_CHECK) <integer> — if required, this parameter should be set using either OSSL_FUNC_asym_cipher_encrypt_init() or OSSL_FUNC_asym_cipher_decrypt_init(). The default value of 1 causes an error during the init if the key is not FIPS approved (e.g. The key has a security strength of less than 112 bits). Setting this to 0 will ignore the error and set the approved "fips-indicator" to 0.
⚠️ Careful, bestie: this option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0. That's not a vibe, that's a compliance problem. 💀

OSSL_FUNC_asym_cipher_gettable_ctx_params() and OSSL_FUNC_asym_cipher_settable_ctx_params() get a constant OSSL_PARAM(3) array that describes the gettable and settable parameters — i.e. the parameters that can be used with OSSL_FUNC_asym_cipherget_ctx_params() and OSSL_FUNC_asym_cipher_set_ctx_params() respectively. Think of it as the menu 📋

⭐ RETURN VALUES ⭐

OSSL_FUNC_asym_cipher_newctx() and OSSL_FUNC_asym_cipher_dupctx() should return the newly created provider side asymmetric cipher context, or NULL on failure. No context, no party 😭

All other functions should return 1 for success or 0 on error. That's it, that's the whole scoring system 🎯

🌈 SEE ALSO 🌈

provider(7)

👑 HISTORY 👑

The provider ASYM_CIPHER interface was introduced in OpenSSL 3.0. The Asymmetric Cipher Parameters "fips-indicator" and "key-check" were added in OpenSSL 3.4. Glow-up timeline, honestly ✨

Okay bestie, we have to do the boring-but-important part now — the receipts, the paperwork, the "yes my lawyer knows my Unix" moment. But it's short, so sip your iced coffee and let's get through it together 💖

Copyright 2019-2025 The OpenSSL Project Authors. All Rights Reserved.

That's the whole squad holding the rights, no cap. And it's licensed under the Apache License 2.0 (the "License"). The exact wording matters here, so read it slow:

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>.

Like, that's not a suggestion, that's the rules 💅 — use it outside the License and you're not in compliance, periodt. The full text lives in the LICENSE file in the source distribution, or you can grab it at the URL above (https://www.openssl.org/source/license.html). Go get it, it's free, it's iconic, it's giving responsible open source citizen 🦋

And that's a wrap on the whole page, bestie! 🎀 You made it through every section — proud of you fr fr. This one came from OpenSSL version 3.5.6, dated 2026-04-07 (yes, that's the date on the tin — don't come for me 🙈). Go forth, encrypt asymmetrically, and remember: reading the manpage is the most main character energy thing you can do ✨👑💜

📦 where this page comes from