.\" $OpenBSD: EVP_PKEY_verify.3,v 1.7 2018/03/23 04:34:23 schwarze Exp $
.\" full merge up to: OpenSSL 48e5119a Jan 19 10:49:22 2018 +0100
.\"
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.Dd $Mdocdate: March 23 2018 $
.Dt EVP_PKEY_VERIFY 3
.Os
.Sh NAME
.Nm EVP_PKEY_verify_init ,
.Nm EVP_PKEY_verify
.Nd signature verification using a public key algorithm
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_PKEY_verify_init
.Fa "EVP_PKEY_CTX *ctx"
.Fc
.Ft int
.Fo EVP_PKEY_verify
.Fa "EVP_PKEY_CTX *ctx"
.Fa "const unsigned char *sig"
.Fa "size_t siglen"
.Fa "const unsigned char *tbs"
.Fa "size_t tbslen"
.Fc
.Sh DESCRIPTION
The
.Fn EVP_PKEY_verify_init
function initializes a public key algorithm context using key
.Fa ctx->pkey
for a signature verification operation.
.Pp
The
.Fn EVP_PKEY_verify
function performs a public key verification operation using
.Fa ctx .
The signature is specified using the
.Fa sig
and
.Fa siglen
parameters.
The verified data (i.e. the data believed originally signed) is
specified using the
.Fa tbs
and
.Fa tbslen
parameters.
.Pp
After the call to
.Fn EVP_PKEY_verify_init ,
algorithm specific control operations can be performed to set any
appropriate parameters for the operation.
.Pp
The function
.Fn EVP_PKEY_verify
can be called more than once on the same context if several operations
are performed using the same parameters.
.Sh RETURN VALUES
.Fn EVP_PKEY_verify_init
and
.Fn EVP_PKEY_verify
return 1 if the verification was successful and 0 if it failed.
Unlike other functions the return value 0 from
.Fn EVP_PKEY_verify
only indicates that the signature did not verify successfully.
That is,
.Fa tbs
did not match the original data or the signature was of invalid form.
It is not an indication of a more serious error.
.Pp
A negative value indicates an error other that signature verification
failure.
In particular, a return value of -2 indicates the operation is not
supported by the public key algorithm.
.Sh EXAMPLES
Verify signature using PKCS#1 and SHA256 digest:
.Bd -literal -offset 3n
#include <openssl/evp.h>
#include <openssl/rsa.h>

EVP_PKEY_CTX *ctx;
unsigned char *md, *sig;
size_t mdlen, siglen;
EVP_PKEY *verify_key;

/*
 * Assumes that verify_key, sig, siglen, md, and mdlen 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_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 */

/* Perform operation */
ret = EVP_PKEY_verify(ctx, sig, siglen, md, mdlen);

/*
 * ret == 1 indicates success, 0 verify failure,
 * and < 0 some other error.
 */
.Ed
.Sh SEE ALSO
.Xr EVP_PKEY_CTX_new 3 ,
.Xr EVP_PKEY_decrypt 3 ,
.Xr EVP_PKEY_derive 3 ,
.Xr EVP_PKEY_encrypt 3 ,
.Xr EVP_PKEY_meth_set_verify 3 ,
.Xr EVP_PKEY_sign 3 ,
.Xr EVP_PKEY_verify_recover 3
.Sh HISTORY
.Fn EVP_PKEY_verify_init
and
.Fn EVP_PKEY_verify
first appeared in OpenSSL 1.0.0 and have been available since
.Ox 4.9 .