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.\" $OpenBSD: RSA_private_encrypt.3,v 1.10 2019/06/10 14:58:48 schwarze Exp $
.\" OpenSSL RSA_private_encrypt.pod b41f6b64 Mar 10 15:49:04 2017 +0000
.\"
.\" This file was written by Ulf Moeller <ulf@openssl.org>.
.\" Copyright (c) 2000 The OpenSSL Project. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in
.\" the documentation and/or other materials provided with the
.\" distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\" software must display the following acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
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.\" endorse or promote products derived from this software without
.\" prior written permission. For written permission, please contact
.\" openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\" nor may "OpenSSL" appear in their names without prior written
.\" permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\" acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
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.Dd $Mdocdate: June 10 2019 $
.Dt RSA_PRIVATE_ENCRYPT 3
.Os
.Sh NAME
.Nm RSA_private_encrypt ,
.Nm RSA_public_decrypt
.Nd low level signature operations
.Sh SYNOPSIS
.In openssl/rsa.h
.Ft int
.Fo RSA_private_encrypt
.Fa "int flen"
.Fa "const unsigned char *from"
.Fa "unsigned char *to"
.Fa "RSA *rsa"
.Fa "int padding"
.Fc
.Ft int
.Fo RSA_public_decrypt
.Fa "int flen"
.Fa "const unsigned char *from"
.Fa "unsigned char *to"
.Fa "RSA *rsa"
.Fa "int padding"
.Fc
.Sh DESCRIPTION
These functions handle RSA signatures at a low level.
.Pp
.Fn RSA_private_encrypt
signs the
.Fa flen
bytes at
.Fa from
(usually a message digest with an algorithm identifier) using the
private key
.Fa rsa
and stores the signature in
.Fa to .
.Fa to
must point to
.Fn RSA_size rsa
bytes of memory.
.Pp
.Fa padding
denotes one of the following modes:
.Bl -tag -width Ds
.It Dv RSA_PKCS1_PADDING
PKCS #1 v1.5 padding.
This function does not handle the
.Sy algorithmIdentifier
specified in PKCS #1.
When generating or verifying PKCS #1 signatures,
.Xr RSA_sign 3
and
.Xr RSA_verify 3
should be used.
.It Dv RSA_NO_PADDING
Raw RSA signature.
This mode should only be used to implement cryptographically sound
padding modes in the application code.
Signing user data directly with RSA is insecure.
.El
.Pp
.Fn RSA_public_decrypt
recovers the message digest from the
.Fa flen
bytes long signature at
.Fa from
using the signer's public key
.Fa rsa .
.Fa to
must point to a memory section large enough to hold the message digest
(which is smaller than
.Fn RSA_size rsa
- 11).
.Fa padding
is the padding mode that was used to sign the data.
.Sh RETURN VALUES
.Fn RSA_private_encrypt
returns the size of the signature (i.e.\&
.Fn RSA_size rsa ) .
.Fn RSA_public_decrypt
returns the size of the recovered message digest.
.Pp
On error, -1 is returned; the error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr RSA_meth_set_priv_enc 3 ,
.Xr RSA_new 3 ,
.Xr RSA_sign 3 ,
.Xr RSA_verify 3
.Sh HISTORY
.Fn RSA_private_encrypt
and
.Fn RSA_public_decrypt
appeared in SSLeay 0.4 or earlier and have been available since
.Ox 2.4 .
.Pp
.Dv RSA_NO_PADDING
is available since SSLeay 0.9.0.
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