EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover_init_ex,
EVP_PKEY_verify_recover - recover signature using a public key algorithm
#include <openssl/evp.h>
int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
int EVP_PKEY_verify_recover_init_ex(EVP_PKEY_CTX *ctx,
const OSSL_PARAM params[]);
int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
unsigned char *rout, size_t *routlen,
const unsigned char *sig, size_t siglen);
EVP_PKEY_verify_recover_init() initializes a public key algorithm context
ctx for signing using the algorithm given when the context was created
using
EVP_PKEY_CTX_new(3) or variants thereof. The algorithm is used to
fetch a
EVP_SIGNATURE method implicitly, see "Implicit fetch"
in
provider(7) for more information about implicit fetches.
EVP_PKEY_verify_recover_init_ex() is the same as
EVP_PKEY_verify_recover_init() but additionally sets the passed
parameters
params on the context before returning.
The
EVP_PKEY_verify_recover() function recovers signed data using
ctx. The signature is specified using the
sig and
siglen
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
rout buffer, if the call is successful recovered data is written to
rout and the amount of data written to
routlen.
Normally an application is only interested in whether a signature verification
operation is successful in those cases the
EVP_verify() function should
be used.
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.
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.
EVP_PKEY_verify_recover_init() and
EVP_PKEY_verify_recover()
return 1 for success and 0 or a negative value for failure. In particular a
return value of -2 indicates the operation is not supported by the public key
algorithm.
Recover digest originally signed using PKCS#1 and SHA256 digest:
#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 */
EVP_PKEY_CTX_new(3),
EVP_PKEY_encrypt(3),
EVP_PKEY_decrypt(3),
EVP_PKEY_sign(3),
EVP_PKEY_verify(3),
EVP_PKEY_derive(3)
The
EVP_PKEY_verify_recover_init() and
EVP_PKEY_verify_recover()
functions were added in OpenSSL 1.0.0.
The
EVP_PKEY_verify_recover_init_ex() function was added in OpenSSL 3.0.
Copyright 2013-2021 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>.