EVP_DIGESTVERIFYINIT(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 NAME 💅

EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal, EVP_DigestVerify — the EVP signature verification girlies ✨ (this is from the OpenSSL manual, section 3ossl, bestie)

🌸 SYNOPSIS 🌸

#include <openssl/evp.h>

int EVP_DigestVerifyInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                            const char *mdname, OSSL_LIB_CTX *libctx,
                            const char *props, EVP_PKEY *pkey,
                            const OSSL_PARAM params[]);
int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                         const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig,
                          size_t siglen);
int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sig,
                     size_t siglen, const unsigned char *tbs, size_t tbslen);

🦋 DESCRIPTION 🦋

okay so the EVP signature routines are like the high-level, main-character interface to digital signatures 💖. The input data gets digested first, and then the signature verification happens. Order matters, bestie.

✨ EVP_DigestVerifyInit_ex() ✨

This one sets up your verification context ctx to use a digest with the name mdname and public key pkey. The name of the digest to be used gets passed to the provider of the signature algorithm in use — and how that provider interprets the digest name is, like, provider specific (iykyk). The provider may implement that digest directly itself, or it may (optionally) choose to fetch it — which could result in a digest from a different provider being selected 👀. If the provider does support fetching the digest, then it may use the props argument for the properties to be used during the fetch. And finally, the passed parameters params, if not NULL, are set on the context before returning.

The pkey algorithm is used to fetch an EVP_SIGNATURE method implicitly, to be used for the actual signing. See "Implicit fetch" in provider(7) for more info about implicit fetches 🫶.

The OpenSSL default and legacy providers support fetching digests and can fetch those digests from any available provider. The OpenSSL FIPS provider also supports fetching digests, but will only fetch digests that are themselves implemented inside the FIPS provider. no cap, that's the rule 🔥.

ctx must be created with EVP_MD_CTX_new() before calling this function. Not optional, bestie.

If pctx is not NULL, the EVP_PKEY_CTX of the verification operation will be written to *pctx — which you can use to set alternative verification options 💅. Note that any existing value in *pctx is overwritten. The EVP_PKEY_CTX value returned must not be freed directly by the application if ctx is not assigned an EVP_PKEY_CTX value before being passed to EVP_DigestVerifyInit_ex() (which means the EVP_PKEY_CTX is created inside EVP_DigestVerifyInit_ex() and it will be freed automatically when the EVP_MD_CTX is freed). If the EVP_PKEY_CTX to be used is created by EVP_DigestVerifyInit_ex then it will use the OSSL_LIB_CTX specified in libctx and the property query string specified in props.

No EVP_PKEY_CTX will be created by EVP_DigestVerifyInit_ex() if the passed ctx has already been assigned one via EVP_MD_CTX_set_pkey_ctx(3). See also SM2(7) 🌸.

🎀 the digest × key type compatibility chart 🎀

Not all digests can be used for all key types — it's giving exclusive guest list. The following combinations apply:

  • DSA — Supports SHA1, SHA224, SHA256, SHA384 and SHA512
  • ECDSA — Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3
  • RSA with no padding — Supports no digests (the digest type must be NULL)
  • RSA with X931 padding — Supports SHA1, SHA256, SHA384 and SHA512
  • All other RSA padding types — Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2, MD4, MDC2, SHA3-224, SHA3-256, SHA3-384, SHA3-512
  • Ed25519 and Ed448 — Support no digests (the digest type must be NULL)
  • HMAC — Supports any digest
  • CMAC, Poly1305 and Siphash — Will ignore any digest provided.

If RSA-PSS is used and restrictions apply then the digest must match. periodt.

💜 EVP_DigestVerifyInit() 💜

Works in the same way as EVP_DigestVerifyInit_ex() except that the mdname parameter will be inferred from the supplied digest type, and props will be NULL. Where supplied, the ENGINE e will be used for the signature verification and digest algorithm implementations. e may be NULL — no pressure.

🧚 the rest of the crew 🧚

  • EVP_DigestVerifyUpdate() — hashes cnt bytes of data at d into the verification context ctx. This function can be called several times on the same ctx to include additional data (slay, streaming).
  • EVP_DigestVerifyFinal() — verifies the data in ctx against the signature in sig of length siglen.
  • EVP_DigestVerify() — verifies tbslen bytes at tbs against the signature in sig of length siglen. one shot, one opportunity.

⭐ RETURN VALUES ⭐

  • EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0 for failure.
  • EVP_DigestVerifyFinal() and EVP_DigestVerify() return 1 for success; any other value indicates failure.

A return value of zero indicates that the signature did not verify successfully (that is, tbs did not match the original data or the signature had an invalid form), while other values indicate a more serious error (and sometimes also indicate an invalid signature form). 😭

The error codes can be obtained from ERR_get_error(3).

🌈 NOTES 🌈

The EVP interface to digital signatures should almost always be used in preference to the low-level interfaces. Why? Because the code then becomes transparent to the algorithm used and much more flexible. main character energy, honestly 👑.

EVP_DigestVerify() is a one shot operation which verifies a single block of data in one function. For algorithms that support streaming it is equivalent to calling EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal(). For algorithms which do not support streaming (e.g. PureEdDSA) it is the only way to verify data. fact check: true 💀.

In previous versions of OpenSSL there was a link between message digest types and public key algorithms. This meant that "clone" digests such as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no longer necessary and the use of clone digest is now discouraged 🙈 (we don't do that anymore).

For some key types and parameters the random number generator must be seeded. If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances (see RAND(7)), the operation will fail.

The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest context. This means that EVP_VerifyUpdate() and EVP_VerifyFinal() can be called later to digest and verify additional data. Applications may disable this behavior by setting the EVP_MD_CTX_FLAG_FINALISE context flag via EVP_MD_CTX_set_flags(3) 🎀.

Note that not all providers support continuation — in case the selected provider does not allow to duplicate contexts, EVP_DigestVerifyFinal() will finalize the digest context and attempting to process additional data via EVP_DigestVerifyUpdate() will result in an error. rude, but okay 💅.

EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex() functions can be called multiple times on a context and the parameters set by previous calls should be preserved if the pkey parameter is NULL. The call then just resets the state of the ctx. cute, low-maintenance.

EVP_DigestVerify() can only be called once, and cannot be used again without reinitialising the EVP_MD_CTX by calling EVP_DigestVerifyInit_ex().

⚠️ Ignoring failure returns of EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex() functions can lead to subsequent undefined behavior when calling EVP_DigestVerifyUpdate(), EVP_DigestVerifyFinal(), or EVP_DigestVerify(). fr fr, check your returns bestie 😭

🌸 SEE ALSO 🌸

EVP_DigestSignInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3), MD5(3), MDC2(3), RIPEMD160(3), SHA1(3), openssl-dgst(1), RAND(7)

🦋 HISTORY 🦋

  • EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() were added in OpenSSL 1.0.0.
  • EVP_DigestVerifyInit_ex() was added in OpenSSL 3.0.
  • EVP_DigestVerifyUpdate() was converted from a macro to a function in OpenSSL 3.0.

Copyright 2006-2024 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>.

okay that's the whole thing bestie, go verify some signatures 💅✨

mwah 💋 — this was page EVP_DIGESTVERIFYINIT(3ossl) from OpenSSL 3.5.0, dated 2026-09-25. it's giving iconic. 🎀

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