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Title "EVP_PKEY_VERIFY_RECOVER 3ossl"
way too many mistakes in technical documents.
\fBEVP_PKEY_verify_recover_init_ex() is the same as \fBEVP_PKEY_verify_recover_init() but additionally sets the passed parameters \fIparams on the context before returning.
\fBEVP_PKEY_verify_recover_init_ex2() is the same as EVP_PKEY_verify_recover_init_ex(), but works with an explicitly fetched EVP_SIGNATURE algo. A context ctx without a pre-loaded key cannot be used with this function. Depending on what algorithm was fetched, certain details revolving around the treatment of the input to EVP_PKEY_verify() may be pre-determined, and in that case, those details may normally not be changed. See "NOTES" below for a deeper explanation.
The EVP_PKEY_verify_recover() function recovers signed data using ctx. The signature is specified using the sig and \fIsiglen parameters. If rout is NULL then the maximum size of the output buffer is written to the routlen parameter. If rout is not NULL then before the call the routlen parameter should contain the length of the \fIrout buffer, if the call is successful recovered data is written to \fIrout and the amount of data written to routlen.
Sometimes however it is useful to obtain the data originally signed using a signing operation. Only certain public key algorithms can recover a signature in this way (for example RSA in PKCS padding mode).
After the call to EVP_PKEY_verify_recover_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation.
After the call to EVP_PKEY_verify_recover_init_ex2(), algorithm specific control operations may not be needed if the chosen algorithm implies that those controls pre-set (and immutable).
The function EVP_PKEY_verify_recover() can be called more than once on the same context if several operations are performed using the same parameters.
.Vb 2 #include <openssl/evp.h> #include <openssl/rsa.h> \& EVP_PKEY_CTX *ctx; unsigned char *rout, *sig; size_t routlen, siglen; EVP_PKEY *verify_key; \& /* * NB: assumes verify_key, sig and siglen are already set up * and that verify_key is an RSA public key */ ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */); if (!ctx) /* Error occurred */ if (EVP_PKEY_verify_recover_init(ctx) <= 0) /* Error */ if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0) /* Error */ if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0) /* Error */ \& /* Determine buffer length */ if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0) /* Error */ \& rout = OPENSSL_malloc(routlen); \& if (!rout) /* malloc failure */ \& if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0) /* Error */ \& /* Recovered data is routlen bytes written to buffer rout */ .Ve
The EVP_PKEY_verify_recover_init_ex() function was added in OpenSSL 3.0.
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>.