EVP_DIGESTVERIFYINIT(3ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

🎀 NAME 🎀

EVP_DigestVerifyInit_ex, EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal, EVP_DigestVerify — the EVP signature verification functions. This is the EVP_DIGESTVERIFYINIT(3ossl) manual page, 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 the high-level interface to digital signatures, and bestie, that is the moment. Input data gets digested first, and then signature verification happens. Periodt.

EVP_DigestVerifyInit_ex() sets up the verification context ctx to use a digest named mdname and public key pkey. The digest name is passed to the provider of the signature algorithm in use, and how that provider interprets the digest name is provider specific. 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 supports fetching the digest, it may use the props argument for the properties to be used during the fetch. Finally, the passed parameters params, if not NULL, are set on the context before returning. Slay.

The pkey algorithm is used to fetch an EVP_SIGNATURE method implicitly, to be used for the actual signing. Peep “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 it will only fetch digests that are themselves implemented inside the FIPS provider. No cap.

ctx must be created with EVP_MD_CTX_new() before calling this function. If pctx is not NULL, the EVP_PKEY_CTX of the verification operation will be written to *pctx — this can be used 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).

Not all digests can be used for all key types, bestie. 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. That's the rule, bestie.

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.

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. Very much “add it to the group chat” energy.

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.

🌈 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).
🚨 Bestie, do not read 0 from EVP_DigestVerifyFinal() or EVP_DigestVerify() as success. 1 is success. Anything else is failure, and some of those failures are extra serious.

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. This is because the code then becomes transparent to the algorithm used and much more flexible. Iconic behavior, 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.

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 have moved on, and honestly, good for us 💅

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 duplicating contexts, EVP_DigestVerifyFinal() will finalize the digest context, and attempting to process additional data via EVP_DigestVerifyUpdate() will result in an error.

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.

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(). Like, fr fr, check the return value.

👑 SEE ALSO 👑

⭐ 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>.

That's the whole page, bestie 🫶 This cuteness was brought to you by OpenSSL 3.5.6, dated 2026-04-07, and the manual page name is EVP_DIGESTVERIFYINIT(3ossl). Stay verified, stay iconic ✨

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