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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_verify 3"
.TH EVP_PKEY_verify 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_PKEY_verify_init, EVP_PKEY_verify \- signature verification using a public key algorithm
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& int EVP_PKEY_verify_init(EVP_PKEY_CTX *ctx);
\& int EVP_PKEY_verify(EVP_PKEY_CTX *ctx,
\&                        const unsigned char *sig, size_t siglen,
\&                        const unsigned char *tbs, size_t tbslen);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBEVP_PKEY_verify_init()\fR function initializes a public key algorithm
context using key \fBpkey\fR for a signature verification operation.
.PP
The \fBEVP_PKEY_verify()\fR function performs a public key verification operation
using \fBctx\fR. The signature is specified using the \fBsig\fR and
\&\fBsiglen\fR parameters. The verified data (i.e. the data believed originally
signed) is specified using the \fBtbs\fR and \fBtbslen\fR parameters.
.SH "NOTES"
.IX Header "NOTES"
After the call to \fBEVP_PKEY_verify_init()\fR algorithm specific control
operations can be performed to set any appropriate parameters for the
operation.
.PP
The function \fBEVP_PKEY_verify()\fR can be called more than once on the same
context if several operations are performed using the same parameters.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_verify_init()\fR and \fBEVP_PKEY_verify()\fR return 1 if the verification was
successful and 0 if it failed. Unlike other functions the return value 0 from
\&\fBEVP_PKEY_verify()\fR only indicates that the signature did not not verify
successfully (that is 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 "EXAMPLE"
.IX Header "EXAMPLE"
Verify signature using PKCS#1 and \s-1SHA256\s0 digest:
.PP
.Vb 2
\& #include <openssl/evp.h>
\& #include <openssl/rsa.h>
\&
\& EVP_PKEY_CTX *ctx;
\& unsigned char *md, *sig;
\& size_t mdlen, siglen; 
\& EVP_PKEY *verify_key;
\& /* NB: assumes 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);
\& 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 for some
\&  * other error.
\&  */
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_encrypt\fR\|(3),
\&\fBEVP_PKEY_decrypt\fR\|(3),
\&\fBEVP_PKEY_sign\fR\|(3),
\&\fBEVP_PKEY_verify_recover\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
These functions were first added to OpenSSL 1.0.0.
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