PROVIDER-DIGEST(7ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💖 NAME 💖

Okay so, bestie: PROVIDER-DIGEST(7ossl) is the OpenSSL manual page for provider-digest, aka the digest library <-> provider functions. This is the provider-side glow-up guide for digest algorithms, and I'm obsessed. 💅

✨ SYNOPSIS ✨

No cap, this is the literal shape of the dispatch table, so copy it exactly. The synopsis ate and left no crumbs:

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

        /*
         * Digests support the following function signatures in OSSL_DISPATCH arrays.
         * (The function signatures are not actual functions).
         */

        /* Context management */
        void *OSSL_FUNC_digest_newctx(void *provctx);
        void OSSL_FUNC_digest_freectx(void *dctx);
        void *OSSL_FUNC_digest_dupctx(void *dctx);
        void OSSL_FUNC_digest_copyctx(void *voutctx, void *vinctx);

        /* Digest generation */
        int OSSL_FUNC_digest_init(void *dctx, const OSSL_PARAM params[]);
        int OSSL_FUNC_digest_update(void *dctx, const unsigned char *in, size_t inl);
        int OSSL_FUNC_digest_final(void *dctx, unsigned char *out, size_t *outl,
                                   size_t outsz);
        int OSSL_FUNC_digest_digest(void *provctx, const unsigned char *in, size_t inl,
                                    unsigned char *out, size_t *outl, size_t outsz);

        /* Digest parameter descriptors */
        const OSSL_PARAM *OSSL_FUNC_digest_gettable_params(void *provctx);

        /* Digest operation parameter descriptors */
        const OSSL_PARAM *OSSL_FUNC_digest_gettable_ctx_params(void *dctx,
                                                               void *provctx);
        const OSSL_PARAM *OSSL_FUNC_digest_settable_ctx_params(void *dctx,
                                                               void *provctx);

        /* Digest parameters */
        int OSSL_FUNC_digest_get_params(OSSL_PARAM params[]);

        /* Digest operation parameters */
        int OSSL_FUNC_digest_set_ctx_params(void *dctx, const OSSL_PARAM params[]);
        int OSSL_FUNC_digest_get_ctx_params(void *dctx, OSSL_PARAM params[]);

🦋 DESCRIPTION 🦋

Fr fr, this documentation is primarily aimed at provider authors. See provider(7) for further information. 🫶

The DIGEST operation lets providers implement digest algorithms and make them available to applications via the API functions EVP_DigestInit_ex(3), EVP_DigestUpdate(3), and EVP_DigestFinal(3) (and other related functions). It's giving "provider plugs in, OpenSSL slays". 👑

All the "functions" mentioned here are passed as function pointers between libcrypto and the provider in OSSL_DISPATCH(3) arrays via OSSL_ALGORITHM(3) arrays that are returned by the provider's provider_query_operation() function (see "Provider Functions" in provider-base(7)). Lowkey the whole provider wiring situation. 💜

All these "functions" have a corresponding function type definition named OSSL_FUNC_{name}_fn, plus a helper function to retrieve the function pointer from an OSSL_DISPATCH(3) element named OSSL_FUNC_{name}. For example, the "function" OSSL_FUNC_digest_newctx() has these:

        typedef void *(OSSL_FUNC_digest_newctx_fn)(void *provctx);
        static ossl_inline OSSL_FUNC_digest_newctx_fn
            OSSL_FUNC_digest_newctx(const OSSL_DISPATCH *opf);

OSSL_DISPATCH(3) arrays are indexed by numbers that are provided as macros in openssl-core_dispatch.h(7), as follows. The way that these line up is iconic:

        OSSL_FUNC_digest_newctx               OSSL_FUNC_DIGEST_NEWCTX
        OSSL_FUNC_digest_freectx              OSSL_FUNC_DIGEST_FREECTX
        OSSL_FUNC_digest_dupctx               OSSL_FUNC_DIGEST_DUPCTX
        OSSL_FUNC_digest_copyctx              OSSL_FUNC_DIGEST_COPYCTX

        OSSL_FUNC_digest_init                 OSSL_FUNC_DIGEST_INIT
        OSSL_FUNC_digest_update               OSSL_FUNC_DIGEST_UPDATE
        OSSL_FUNC_digest_final                OSSL_FUNC_DIGEST_FINAL
        OSSL_FUNC_digest_digest               OSSL_FUNC_DIGEST_DIGEST

        OSSL_FUNC_digest_get_params           OSSL_FUNC_DIGEST_GET_PARAMS
        OSSL_FUNC_digest_get_ctx_params       OSSL_FUNC_DIGEST_GET_CTX_PARAMS
        OSSL_FUNC_digest_set_ctx_params       OSSL_FUNC_DIGEST_SET_CTX_PARAMS

        OSSL_FUNC_digest_gettable_params      OSSL_FUNC_DIGEST_GETTABLE_PARAMS
        OSSL_FUNC_digest_gettable_ctx_params  OSSL_FUNC_DIGEST_GETTABLE_CTX_PARAMS
        OSSL_FUNC_digest_settable_ctx_params  OSSL_FUNC_DIGEST_SETTABLE_CTX_PARAMS

A digest algorithm implementation may not implement all of these functions. In order to be usable, all or none of OSSL_FUNC_digest_newctx, OSSL_FUNC_digest_freectx, OSSL_FUNC_digest_init, OSSL_FUNC_digest_update, OSSL_FUNC_digest_final, and OSSL_FUNC_digest_get_params should be implemented. Ngl, that all-or-none part is highkey important. 😭 Vibe check: all other functions are optional. 💖

🫶 Context Management Functions 🫶

OSSL_FUNC_digest_newctx() should create and return a pointer to a provider side structure for holding context information during a digest operation. A pointer to this context will be passed back in a number of the other digest operation function calls. The parameter provctx is the provider context generated during provider initialisation (see provider(7)). ✨

OSSL_FUNC_digest_freectx() is passed a pointer to the provider side digest context in the dctx parameter. This function should free any resources associated with that context. 💀

OSSL_FUNC_digest_dupctx() should duplicate the provider side digest context in the dctx parameter and return the duplicate copy. 💖

OSSL_FUNC_digest_copyctx() should copy the provider side digest context in the vinctx parameter to the voutctx parameter, which is another provider side context. The OSSL_FUNC_digest_copyctx function is used in the EVP_MD_CTX_copy_ex function to speed up HMAC operations in the PBKDF2. This function is optional, and dupctx will be used if there is no EVP_MD_CTX_copy_ex function. Iykyk. 🌀

🌸 Digest Generation Functions 🌸

OSSL_FUNC_digest_init() initialises a digest operation given a newly created provider side digest context in the dctx parameter. The params, if not NULL, should be set on the context in a manner similar to using OSSL_FUNC_digest_set_ctx_params(). 🎀

OSSL_FUNC_digest_update() is called to supply data to be digested as part of a previously initialised digest operation. The dctx parameter contains a pointer to a previously initialised provider side context. OSSL_FUNC_digest_update() should digest inl bytes of data at the location pointed to by in. OSSL_FUNC_digest_update() may be called multiple times for a single digest operation. 🔥

OSSL_FUNC_digest_final() generates a digest started through previous OSSL_FUNC_digest_init() and OSSL_FUNC_digest_update() calls. The dctx parameter contains a pointer to the provider side context. The digest should be written to *out and the length of the digest to *outl. The digest should not exceed outsz bytes. 🎀

OSSL_FUNC_digest_digest() is a "oneshot" digest function. No provider side digest context is used. Instead the provider context that was created during provider initialisation is passed in the provctx parameter (see provider(7)). inl bytes at in should be digested and the result should be stored at out. The length of the digest should be stored in *outl which should not exceed outsz bytes. ⭐

🍓 Digest Parameters 🍓

See OSSL_PARAM(3) for further details on the parameters structure used by these functions. 🫶

OSSL_FUNC_digest_get_params() gets details of the algorithm implementation and stores them in params. 💅

OSSL_FUNC_digest_set_ctx_params() sets digest operation parameters for the provider side digest context dctx to params. Any parameter settings are additional to any that were previously set. Passing NULL for params should return true. ✨

OSSL_FUNC_digest_get_ctx_params() gets digest operation details-details (yes, twice, that's the vibe) from the given provider side digest context dctx and stores them in params. Passing NULL for params should return true. 🙈

OSSL_FUNC_digest_gettable_params() returns a constant OSSL_PARAM(3) array containing descriptors of the parameters that OSSL_FUNC_digest_get_params() can handle. 🎀

OSSL_FUNC_digest_gettable_ctx_params() and OSSL_FUNC_digest_settable_ctx_params() both return constant OSSL_PARAM(3) arrays as descriptors of the parameters that OSSL_FUNC_digest_get_ctx_params() and OSSL_FUNC_digest_set_ctx_params() can handle, respectively. The array is based on the current state of the provider side context if dctx is not NULL and on the provider side algorithm provctx otherwise. 💜

Parameters currently recognised by built-in digests with this function are as follows. Not all parameters are relevant to, or are understood by all digests: 🌈

  • "blocksize" (OSSL_DIGEST_PARAM_BLOCK_SIZE) <unsigned integer> — the digest block size. The length of the "blocksize" parameter should not exceed that of a size_t. 🍓
  • "size" (OSSL_DIGEST_PARAM_SIZE) <unsigned integer> — the digest output size. The length of the "size" parameter should not exceed that of a size_t. 🍓
  • "flags" (OSSL_DIGEST_PARAM_FLAGS) <unsigned integer> — diverse flags that describe exceptional behaviour for the digest:
    • EVP_MD_FLAG_ONESHOT — this digest method can only handle one block of input.
    • EVP_MD_FLAG_XOF — this digest method is an extensible-output function (XOF).
    • EVP_MD_FLAG_DIGALGID_NULL — when setting up a DigestAlgorithmIdentifier, this flag will have the parameter set to NULL by default. Use this for PKCS#1. Note: if combined with EVP_MD_FLAG_DIGALGID_ABSENT, the latter will override.
    • EVP_MD_FLAG_DIGALGID_ABSENT — when setting up a DigestAlgorithmIdentifier, this flag will have the parameter be left absent by default. Note: if combined with EVP_MD_FLAG_DIGALGID_NULL, the latter will be overridden.
    • EVP_MD_FLAG_DIGALGID_CUSTOM — custom DigestAlgorithmIdentifier handling via ctrl, with EVP_MD_FLAG_DIGALGID_ABSENT as default. Note: if combined with EVP_MD_FLAG_DIGALGID_NULL, the latter will be overridden. Currently unused.

The length of the "flags" parameter should equal that of an unsigned long int. 💅

🧚 Digest Context Parameters 🧚

OSSL_FUNC_digest_set_ctx_params() sets digest parameters associated with the given provider side digest context dctx to params. Any parameter settings are additional to any that were previously set. See OSSL_PARAM(3) for further details on the parameters structure. 🫶

OSSL_FUNC_digest_get_ctx_params() gets details of currently set parameter values associated with the given provider side digest context dctx and stores them in params. See OSSL_PARAM(3) for further details on the parameters structure. ✨

🌈 RETURN VALUES 🌈

  • OSSL_FUNC_digest_newctx() and OSSL_FUNC_digest_dupctx() should return the newly created provider side digest context, or NULL on failure. 💖
  • OSSL_FUNC_digest_init(), OSSL_FUNC_digest_update(), OSSL_FUNC_digest_final(), OSSL_FUNC_digest_digest(), OSSL_FUNC_digest_set_params(), and OSSL_FUNC_digest_get_params() should return 1 for success or 0 on error. ⭐
  • OSSL_FUNC_digest_size() should return the digest size. 🍓
  • OSSL_FUNC_digest_block_size() should return the block size of the underlying digest algorithm. 🎀

🐛 BUGS 🐛

okay so this is the part where we have to be real with each other 💀

  • EVP_Q_digest(), EVP_Digest() and EVP_DigestFinal_ex() literally do not expect the digest size to be bigger than EVP_MAX_MD_SIZE. like, they just don't.
  • which means any algorithm that produces larger digests is unusable with those API calls. periodt. no workaround, no sneaky fix, it's just not happening bestie 😭
fr fr read this before you go picking some giant-digest algorithm and wondering why nothing works. that's not a vibe, that's a bug.

👀 SEE ALSO 👀

go read these next, i promise they're worth it 🫶

like that's the whole squad 💅 every single one of them, no skips, we don't do that here.

📜 HISTORY 📜

a lil lore drop for you, bestie ✨

  • the provider DIGEST interface was introduced in OpenSSL 3.0
  • OSSL_FUNC_digest_copyctx() was added in 3.5 version

so yeah, if you're on something older than 3.5 and you're looking for OSSL_FUNC_digest_copyctx(), that's why it's giving invisible 😭 it's not you, it's the version.

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

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.

ngl the "except in compliance with the License" part is the legal version of "read the rules before you post". iconic behavior, honestly 👑

aaaand that's a wrap on PROVIDER-DIGEST(7ossl) 🎀 this page is version 3.5.0, dated 2026-09-25 — go forth and digest responsibly, bestie 💖✨🦋

📦 where this page comes from