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¶
The
EVP_PKEY_verify_recover_init() function initializes a public key
algorithm context using key
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.
NOTES¶
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.
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.
EXAMPLE¶
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);
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 */
SEE ALSO¶
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)
HISTORY¶
These functions were first added to OpenSSL 1.0.0.