PROVIDER-ASYM_CIPHER(7ossl)

📦 version 3.5.0, in opensuse-leap 16.0

✨ NAME ✨

okay bestie, welcome to provider-asym_cipher — the 7ossl manual page — and it's literally all about The asym_cipher library <-> provider functions. that's the whole vibe: it's the bridge between the asym_cipher library and the provider-side functions, iykyk 💅

🦋 SYNOPSIS 🦋

so first things first, you gotta pull in these headers:

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

and here's the full function-pointer lineup, copied exactly, no cap:

/*
 * 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);

quick vibe check, bestie: those aren't actual functions you call directly — they're displayed like this to show the function signatures for stuff that gets offered as function pointers inside OSSL_DISPATCH arrays. that's the whole point, and it's kind of iconic honestly 🫶

part 2 is coming with more deets, so keep reading ✨

💖 DESCRIPTION 💖

okay so bestie, real talk: this whole page is for provider authors, like the people actually building the crypto guts. If that's not you yet, go peek at provider(7) first, k? 🫶

The asymmetric cipher operation (OSSL_OP_ASYM_CIPHER) is literally what lets providers implement asymmetric cipher algorithms and serve them up to applications through the API functions EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3), and all their little friends.

Every single "function" we talk about here gets passed as a function pointer between libcrypto and the provider inside OSSL_DISPATCH(3) arrays, which come back through OSSL_ALGORITHM(3) arrays returned by the provider's provider_query_operation() function (peep "Provider Functions" in provider-base(7) for the deets). ✨

Each of these "functions" has a matching function type definition named OSSL_FUNC_{name}_fn, plus a helper to grab the function pointer out of an OSSL_DISPATCH(3) element named OSSL_FUNC_{name}. Like, for the "function" OSSL_FUNC_asym_cipher_newctx() you get these:

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 that show up as macros in openssl-core_dispatch.h(7), like this 👇

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 implementation doesn't have to implement every single one of these — but there are rules, and the vibes must be consistent. A provider must implement OSSL_FUNC_asym_cipher_newctx and OSSL_FUNC_asym_cipher_freectx. It must also implement both OSSL_FUNC_asym_cipher_encrypt_init and OSSL_FUNC_asym_cipher_encrypt, or both OSSL_FUNC_asym_cipher_decrypt_init and OSSL_FUNC_asym_cipher_decrypt. OSSL_FUNC_asym_cipher_get_ctx_params is optional, but if it's there then OSSL_FUNC_asym_cipher_gettable_ctx_params has to be there too. Same story: OSSL_FUNC_asym_cipher_set_ctx_params is optional, but if it's present then OSSL_FUNC_asym_cipher_settable_ctx_params must be too. package deal, no splitting the set 💅

Also, an asymmetric cipher algorithm has to implement some mechanism for generating, loading, or importing keys via the key management (OSSL_OP_KEYMGMT) operation. provider-keymgmt(7) has the full tea. 🫖

🎀 Context Management Functions 🎀

OSSL_FUNC_asym_cipher_newctx() should create and return a pointer to a provider-side structure that holds context info during an asymmetric cipher operation. That pointer gets passed back into a bunch of the other asymmetric cipher operation function calls. The provctx parameter is the provider context created during provider initialisation (see provider(7)). ✨

OSSL_FUNC_asym_cipher_freectx() gets handed a pointer to the provider-side asymmetric cipher context in the ctx parameter. This function should free any resources tied to that context. 🧹

OSSL_FUNC_asym_cipher_dupctx() should duplicate the provider-side asymmetric cipher context in the ctx parameter and return the duplicate copy. 🦋

🔥 Encryption Functions 🔥

OSSL_FUNC_asym_cipher_encrypt_init() initialises a context for 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 previously been generated, loaded, or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

OSSL_FUNC_asym_cipher_encrypt() does the actual encryption itself. A previously initialised asymmetric cipher context comes in via the ctx parameter. The data to encrypt is pointed to by the in parameter, which is inlen bytes long. Unless out is NULL, the encrypted data should be written to where the out parameter points, 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. 👑

🌸 Decryption Functions 🌸

OSSL_FUNC_asym_cipher_decrypt_init() initialises a context for 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 previously been generated, loaded, or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)).

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 decrypt 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. If out is NULL, then the maximum length of the decrypted data should be written to *outlen.

💜 Asymmetric Cipher Parameters 💜

Check out OSSL_PARAM(3) for more details on the parameters structure used by OSSL_FUNC_asym_cipher_get_ctx_params() and OSSL_FUNC_asym_cipher_set_ctx_params().

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.

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 anything previously set. Passing NULL for params should return true. ✨

The parameters currently recognised by built-in asymmetric cipher algorithms are these. Heads up though: not all parameters are relevant to, or understood by, all asymmetric cipher algorithms. 🙈

  • "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.
  • "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.
  • "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.
  • "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 a side-channel free manner. Set by default in OpenSSL providers. 🔥

The OpenSSL FIPS provider also supports these 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.
⚠️ bestie this one matters: this option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0. 😭

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. parameters that can be used with OSSL_FUNC_asym_cipherget_ctx_params() and OSSL_FUNC_asym_cipher_set_ctx_params() respectively. 📋

⭐ 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. 💀

All other functions should return 1 for success or 0 on error.

🌈 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. 🎀

Okay bestie, legal era incoming, but it's actually short so stay with me 💅

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

That's the whole vibe: the OpenSSL Project Authors hold the rights, the years are 2019 through 2025, and that "All Rights Reserved" is doing its little iconic thing at the end. 🔥

Then the licensing bit — and this one's important, so no skimming 🙈

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, that's the actual rule: use it outside the License and you're not in compliance. Lowkey the whole point of the sentence. The LICENSE file lives in the source distribution, and the URL is the online copy — both paths are right there for you 🫶

And that's the page, bestie — you made it to the very end!! 🎉🦋 This was PROVIDER-ASYM_CIPHER(7ossl), the OpenSSL 3.5.0 edition, dated 2026-09-25. Go forth and encrypt asymmetrically, you absolute main character 👑✨💖

📦 where this page comes from