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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_SIGN 3"
.TH EVP_PKEY_SIGN 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
EVP_PKEY_sign_init, EVP_PKEY_sign \- sign using a public key algorithm
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& int EVP_PKEY_sign_init(EVP_PKEY_CTX *ctx);
\& int EVP_PKEY_sign(EVP_PKEY_CTX *ctx,
\&                   unsigned char *sig, size_t *siglen,
\&                   const unsigned char *tbs, size_t tbslen);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBEVP_PKEY_sign_init()\fR function initializes a public key algorithm
context using key \fBpkey\fR for a signing operation.
.PP
The \fBEVP_PKEY_sign()\fR function performs a public key signing operation
using \fBctx\fR. The data to be signed is specified using the \fBtbs\fR and
\&\fBtbslen\fR parameters. If \fBsig\fR is \fB\s-1NULL\s0\fR then the maximum size of the output
buffer is written to the \fBsiglen\fR parameter. If \fBsig\fR is not \fB\s-1NULL\s0\fR then
before the call the \fBsiglen\fR parameter should contain the length of the
\&\fBsig\fR buffer, if the call is successful the signature is written to
\&\fBsig\fR and the amount of data written to \fBsiglen\fR.
.SH "NOTES"
.IX Header "NOTES"
\&\fBEVP_PKEY_sign()\fR does not hash the data to be signed, and therefore is
normally used to sign digests. For signing arbitrary messages, see the
\&\fBEVP_DigestSignInit\fR\|(3) and
\&\fBEVP_SignInit\fR\|(3) signing interfaces instead.
.PP
After the call to \fBEVP_PKEY_sign_init()\fR algorithm specific control
operations can be performed to set any appropriate parameters for the
operation (see \fBEVP_PKEY_CTX_ctrl\fR\|(3)).
.PP
The function \fBEVP_PKEY_sign()\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_sign_init()\fR and \fBEVP_PKEY_sign()\fR 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.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Sign data using \s-1RSA\s0 with PKCS#1 padding and \s-1SHA256\s0 digest:
.PP
.Vb 2
\& #include <openssl/evp.h>
\& #include <openssl/rsa.h>
\&
\& EVP_PKEY_CTX *ctx;
\& /* md is a SHA\-256 digest in this example. */
\& unsigned char *md, *sig;
\& size_t mdlen = 32, siglen;
\& EVP_PKEY *signing_key;
\&
\& /*
\&  * NB: assumes signing_key and md are set up before the next
\&  * step. signing_key must be an RSA private key and md must
\&  * point to the SHA\-256 digest to be signed.
\&  */
\& ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);
\& if (!ctx)
\&     /* Error occurred */
\& if (EVP_PKEY_sign_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_sign(ctx, NULL, &siglen, md, mdlen) <= 0)
\&     /* Error */
\&
\& sig = OPENSSL_malloc(siglen);
\&
\& if (!sig)
\&     /* malloc failure */
\&
\& if (EVP_PKEY_sign(ctx, sig, &siglen, md, mdlen) <= 0)
\&     /* Error */
\&
\& /* Signature is siglen bytes written to buffer sig */
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_CTX_ctrl\fR\|(3),
\&\fBEVP_PKEY_encrypt\fR\|(3),
\&\fBEVP_PKEY_decrypt\fR\|(3),
\&\fBEVP_PKEY_verify\fR\|(3),
\&\fBEVP_PKEY_verify_recover\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
These functions were added in OpenSSL 1.0.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2006\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.