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.\" ========================================================================
.\"
.IX Title "RSA_private_encrypt 3"
.TH RSA_private_encrypt 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.
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.nh
.SH "NAME"
RSA_private_encrypt, RSA_public_decrypt \- low level signature operations
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rsa.h>
\&
\& int RSA_private_encrypt(int flen, const unsigned char *from,
\&    unsigned char *to, RSA *rsa, int padding);
\&
\& int RSA_public_decrypt(int flen, const unsigned char *from,
\&    unsigned char *to, RSA *rsa, int padding);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
These functions handle \s-1RSA\s0 signatures at a low level.
.PP
\&\fBRSA_private_encrypt()\fR signs the \fBflen\fR bytes at \fBfrom\fR (usually a
message digest with an algorithm identifier) using the private key
\&\fBrsa\fR and stores the signature in \fBto\fR. \fBto\fR must point to
\&\fBRSA_size(rsa)\fR bytes of memory.
.PP
\&\fBpadding\fR denotes one of the following modes:
.IP "\s-1RSA_PKCS1_PADDING\s0" 4
.IX Item "RSA_PKCS1_PADDING"
\&\s-1PKCS\s0 #1 v1.5 padding. This function does not handle the
\&\fBalgorithmIdentifier\fR specified in \s-1PKCS\s0 #1. When generating or
verifying \s-1PKCS\s0 #1 signatures, \fBRSA_sign\fR\|(3) and \fBRSA_verify\fR\|(3) should be
used.
.IP "\s-1RSA_NO_PADDING\s0" 4
.IX Item "RSA_NO_PADDING"
Raw \s-1RSA\s0 signature. This mode should \fIonly\fR be used to implement
cryptographically sound padding modes in the application code.
Signing user data directly with \s-1RSA\s0 is insecure.
.PP
\&\fBRSA_public_decrypt()\fR recovers the message digest from the \fBflen\fR
bytes long signature at \fBfrom\fR using the signer's public key
\&\fBrsa\fR. \fBto\fR must point to a memory section large enough to hold the
message digest (which is smaller than \fBRSA_size(rsa) \-
11\fR). \fBpadding\fR is the padding mode that was used to sign the data.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBRSA_private_encrypt()\fR returns the size of the signature (i.e.,
RSA_size(rsa)). \fBRSA_public_decrypt()\fR returns the size of the
recovered message digest.
.PP
On error, \-1 is returned; the error codes can be
obtained by \fBERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBERR_get_error\fR\|(3), \fBrsa\fR\|(3),
\&\fBRSA_sign\fR\|(3), \fBRSA_verify\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
The \fBpadding\fR argument was added in SSLeay 0.8. \s-1RSA_NO_PADDING\s0 is
available since SSLeay 0.9.0.