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EVP_PKEY_VERIFY_RECOVER(3) | Library Functions Manual | EVP_PKEY_VERIFY_RECOVER(3) |
NAME
EVP_PKEY_verify_recover_init
,
EVP_PKEY_verify_recover
—
recover signature using a public key algorithm
SYNOPSIS
#include
<openssl/evp.h>
int
EVP_PKEY_verify_recover_init
(EVP_PKEY_CTX
*ctx);
int
EVP_PKEY_verify_recover
(EVP_PKEY_CTX
*ctx, unsigned char *rout,
size_t *routlen,
const unsigned char *sig,
size_t siglen);
DESCRIPTION
TheEVP_PKEY_verify_recover_init
() function
initializes a public key algorithm context using key
ctx->pkey for a verify recover operation.
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_PKEY_verify(3)
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.
RETURN VALUES
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.
EXAMPLES
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; /* * Assumes that 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); 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 = 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 */
SEE ALSO
EVP_PKEY_CTX_new(3), EVP_PKEY_decrypt(3), EVP_PKEY_derive(3), EVP_PKEY_encrypt(3), EVP_PKEY_meth_set_verify_recover(3), EVP_PKEY_sign(3), EVP_PKEY_verify(3)HISTORY
EVP_PKEY_verify_recover_init
() and
EVP_PKEY_verify_recover
() first appeared in
OpenSSL 1.0.0 and have been available since OpenBSD
4.9.March 23, 2018 | Debian |