EVP_VERIFYINIT(3ossl)

💖 EVP_VERIFYINIT 💖

okay bestie, gather round, because we're about to talk about OpenSSL signature verification and honestly? it's giving main character energy. this is the 3ossl manual page for EVP_VerifyInit_ex, EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal_ex, and EVP_VerifyFinal — the EVP signature verification functions. yes, all five of them, they're a little friend group 🫶

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✨ NAME ✨

EVP_VerifyInit_ex, EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal_ex, EVP_VerifyFinal — EVP signature verification functions. no cap, that's the whole squad.

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✨ SYNOPSIS ✨

#include <openssl/evp.h>

int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
int EVP_VerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
int EVP_VerifyFinal_ex(EVP_MD_CTX *ctx, const unsigned char *sigbuf,
                       unsigned int siglen, EVP_PKEY *pkey,
                       OSSL_LIB_CTX *libctx, const char *propq);
int EVP_VerifyFinal(EVP_MD_CTX *ctx, unsigned char *sigbuf, unsigned int siglen,
                    EVP_PKEY *pkey);

int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);

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✨ DESCRIPTION ✨

so. the EVP signature verification routines are a high-level interface to digital signatures. that's the whole vibe. you don't gotta touch the scary low-level stuff, EVP handles it 💅

EVP_VerifyInit_ex() sets up verification context ctx to use digest type from ENGINE impl. and listen — ctx must be created by calling EVP_MD_CTX_new() before you call this function. don't skip that step bestie, it will not go well 😭

EVP_VerifyUpdate() hashes cnt bytes of data at d into the verification context ctx. you can call this function several times on the same ctx to include additional data. it's a "keep adding to the pile" situation, iconic behavior honestly 🎀

EVP_VerifyFinal_ex() verifies the data in ctx using the public key pkey and siglen bytes in sigbuf. the library context libctx and property query propq are used when creating a context to use with the key pkey. very demure, very mindful, very configurable ✨

EVP_VerifyFinal() is similar to EVP_VerifyFinal_ex() but uses default values of NULL for the library context libctx and the property query propq. it's the low-effort version and honestly? valid.

EVP_VerifyInit() initializes verification context ctx to use the default implementation of digest type.

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✨ RETURN VALUES ✨

okay so here's the scoreboard 🏆

• EVP_VerifyInit_ex() and EVP_VerifyUpdate() return 1 for success and 0 for failure.
• EVP_VerifyFinal_ex() and EVP_VerifyFinal() return 1 for a correct signature, 0 for failure and a negative value if some other error occurred. so like, three different outcomes, it's giving "it's complicated" 💀

the error codes can be obtained by ERR_get_error(3).

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✨ 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. glow-up behavior fr fr 🌈

the call to EVP_VerifyFinal() internally finalizes a copy of the digest context. this means that calls to 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).

⚠️ since only a copy of the digest context is ever finalized, the context must be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak will occur. bestie. please. free your context. do it for me 🙈

note that not all providers support continuation. in case the selected provider does not allow to duplicate contexts, EVP_VerifyFinal() will finalize the digest context and attempting to process additional data via EVP_VerifyUpdate() will result in an error. so like, read the room and check your provider 💅

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✨ BUGS ✨

• older versions of this documentation wrongly stated that calls to EVP_VerifyUpdate() could not be made after calling EVP_VerifyFinal(). the docs lied, we've moved on, it's fine 💀
• since the public key is passed in the call to EVP_SignFinal() any error relating to the private key (for example an unsuitable key and digest combination) will not be indicated until after potentially large amounts of data have been passed through EVP_SignUpdate(). yeah that's a lot of processing before you find out something's wrong, tragic honestly 😭
• it is not possible to change the signing parameters using these function.

the previous two bugs are fixed in the newer EVP_DigestVerify*() function. so if you want the upgraded version, that's where it's at ✨

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✨ SEE ALSO ✨

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

(yes, evp(7) is in there twice. that's the original. we don't edit, we preserve 🫶)

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✨ HISTORY ✨

the function EVP_VerifyFinal_ex() was added in OpenSSL 3.0. baby of the family, new gen, we love to see it 🌸

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✨ COPYRIGHT ✨

Copyright 2000-2023 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>.

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and that's a wrap on the whole thing, bestie 🎀 this was OpenSSL version 3.5.9, dated 2026-09-29, and yes the manpage title is EVP_VERIFYINIT(3ossl) because of course it is. go verify some signatures, free your EVP_MD_CTX, and slay 💖✨👑