EVP_VERIFYINIT(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💖 EVP_VERIFYINIT(3ossl) — the OpenSSL bestie verification era 💖

okay so this is the tea on EVP_VERIFYINIT from the OpenSSL manual (3ossl, yes we're fancy) — it's the whole signature-verification friend group and honestly they're iconic. Let's get into it 🫶

✨ NAME ✨

EVP_VerifyInit_ex, EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal_ex, EVP_VerifyFinal — the EVP signature verification functions, aka the girlies who check that a signature is actually valid 💅

🦋 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);

like, copy-paste these exactly bestie, sigbuf is unsigned char * in EVP_VerifyFinal but const unsigned char * in EVP_VerifyFinal_ex and that is NOT a typo, that's just how it is 🙈

🌸 DESCRIPTION 🌸

The EVP signature verification routines are a high-level interface to digital signatures. high-level meaning the main character energy version — you don't gotta deal with the low-level mess 🎀

  • 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. no skipping steps bestie, the context has to already exist ✨
  • EVP_VerifyUpdate() — hashes cnt bytes of data at d into the verification context ctx. you can call this several times on the same ctx to pile on more data, so go off, feed her data in chunks, she can take it 💪
  • 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 get used when creating a context to use with the key pkey 🦋
  • EVP_VerifyFinal() — literally the same vibe as EVP_VerifyFinal_ex() except it uses the default values of NULL for the library context libctx and the property query propq. so like, the no-frills version 💅
  • EVP_VerifyInit() — initializes verification context ctx to use the default implementation of digest type 🌈

🔥 RETURN VALUES 🔥

  • EVP_VerifyInit_ex() and EVP_VerifyUpdate() — return 1 for success and 0 for failure. simple. binary. slay ✨
  • EVP_VerifyFinal_ex() and EVP_VerifyFinal() — return 1 for a correct signature, 0 for failure, and a negative value if some other error occurred. yes she has three moods, get used to it 😭

you can grab the error codes with ERR_get_error(3) — that's your receipts, keep them 🧾

💜 NOTES 💜

okay important stuff, pay attention:

  • 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. it's giving "write once, algorithm-agnostic, unbothered" 👑
  • The call to EVP_VerifyFinal() internally finalizes a copy of the digest context. which means calls to EVP_VerifyUpdate() and EVP_VerifyFinal() can be called later to digest and verify additional data. so you're not locked out after the finale, periodt 💅
  • Applications may disable this behavior by setting the EVP_MD_CTX_FLAG_FINALISE context flag via EVP_MD_CTX_set_flags(3). your choice bestie, but know what you're doing 🎀
⚠️ 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. no cap, that's a leak. she will haunt you. free her 💀
  • Note that not all providers support continuation. in case the selected provider does not allow duplicating contexts, EVP_VerifyFinal() will finalize the digest context and attempting to process additional data via EVP_VerifyUpdate() will result in an error. so like, vibe check your provider first 🙈

💀 BUGS 💀

the lore, gather round:

  • Older versions of this documentation wrongly stated that calls to EVP_VerifyUpdate() could not be made after calling EVP_VerifyFinal(). that was a lie, the docs were lying, we're all healing 🫶
  • 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(). awkward. iconic. terrible 😭
  • It is not possible to change the signing parameters using these function. (their grammar, not mine, we keep it verbatim, we respect the source 💅)
  • The previous two bugs are fixed in the newer EVP_DigestVerify*() functions. glow-up confirmed ✨

⭐ 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, and no I'm not fixing it, the source said what it said 👑)

🧚 HISTORY 🧚

The function EVP_VerifyFinal_ex() was added in OpenSSL 3.0. she's the newer sister, show some respect 🌸

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>.

and that's the whole page bestie 💖 mwah, go verify something. this one's stamped 3.5.0 and dated 2026-09-25, so like, future energy, we love to see it 🦋✨🎀

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