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.\" ========================================================================
.\"
.IX Title "RSA_PUBLIC_ENCRYPT 3"
.TH RSA_PUBLIC_ENCRYPT 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.nh
.SH "NAME"
RSA_public_encrypt, RSA_private_decrypt \- RSA public key cryptography
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rsa.h>
\&
\& int RSA_public_encrypt(int flen, const unsigned char *from,
\& unsigned char *to, RSA *rsa, int padding);
\&
\& int RSA_private_decrypt(int flen, const unsigned char *from,
\& unsigned char *to, RSA *rsa, int padding);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBRSA_public_encrypt()\fR encrypts the \fBflen\fR bytes at \fBfrom\fR (usually a
session key) using the public key \fBrsa\fR and stores the ciphertext in
\&\fBto\fR. \fBto\fR must point to RSA_size(\fBrsa\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 currently is the most widely used mode.
However, it is highly recommended to use \s-1RSA_PKCS1_OAEP_PADDING\s0 in
new applications. \s-1SEE WARNING BELOW.\s0
.IP "\s-1RSA_PKCS1_OAEP_PADDING\s0" 4
.IX Item "RSA_PKCS1_OAEP_PADDING"
EME-OAEP as defined in \s-1PKCS\s0 #1 v2.0 with \s-1SHA\-1, MGF1\s0 and an empty
encoding parameter. This mode is recommended for all new applications.
.IP "\s-1RSA_SSLV23_PADDING\s0" 4
.IX Item "RSA_SSLV23_PADDING"
\&\s-1PKCS\s0 #1 v1.5 padding with an SSL-specific modification that denotes
that the server is \s-1SSL3\s0 capable.
.IP "\s-1RSA_NO_PADDING\s0" 4
.IX Item "RSA_NO_PADDING"
Raw \s-1RSA\s0 encryption. This mode should \fIonly\fR be used to implement
cryptographically sound padding modes in the application code.
Encrypting user data directly with \s-1RSA\s0 is insecure.
.PP
\&\fBflen\fR must not be more than RSA_size(\fBrsa\fR) \- 11 for the \s-1PKCS\s0 #1 v1.5
based padding modes, not more than RSA_size(\fBrsa\fR) \- 42 for
\&\s-1RSA_PKCS1_OAEP_PADDING\s0 and exactly RSA_size(\fBrsa\fR) for \s-1RSA_NO_PADDING.\s0
When a padding mode other than \s-1RSA_NO_PADDING\s0 is in use, then
\&\fBRSA_public_encrypt()\fR will include some random bytes into the ciphertext
and therefore the ciphertext will be different each time, even if the
plaintext and the public key are exactly identical.
The returned ciphertext in \fBto\fR will always be zero padded to exactly
RSA_size(\fBrsa\fR) bytes.
\&\fBto\fR and \fBfrom\fR may overlap.
.PP
\&\fBRSA_private_decrypt()\fR decrypts the \fBflen\fR bytes at \fBfrom\fR using the
private key \fBrsa\fR and stores the plaintext in \fBto\fR. \fBflen\fR should
be equal to RSA_size(\fBrsa\fR) but may be smaller, when leading zero
bytes are in the ciphertext. Those are not important and may be removed,
but \fBRSA_public_encrypt()\fR does not do that. \fBto\fR must point
to a memory section large enough to hold the maximal possible decrypted
data (which is equal to RSA_size(\fBrsa\fR) for \s-1RSA_NO_PADDING,\s0
RSA_size(\fBrsa\fR) \- 11 for the \s-1PKCS\s0 #1 v1.5 based padding modes and
RSA_size(\fBrsa\fR) \- 42 for \s-1RSA_PKCS1_OAEP_PADDING\s0).
\&\fBpadding\fR is the padding mode that was used to encrypt the data.
\&\fBto\fR and \fBfrom\fR may overlap.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBRSA_public_encrypt()\fR returns the size of the encrypted data (i.e.,
RSA_size(\fBrsa\fR)). \fBRSA_private_decrypt()\fR returns the size of the
recovered plaintext. A return value of 0 is not an error and
means only that the plaintext was empty.
.PP
On error, \-1 is returned; the error codes can be
obtained by \fBERR_get_error\fR\|(3).
.SH "WARNINGS"
.IX Header "WARNINGS"
Decryption failures in the \s-1RSA_PKCS1_PADDING\s0 mode leak information
which can potentially be used to mount a Bleichenbacher padding oracle
attack. This is an inherent weakness in the \s-1PKCS\s0 #1 v1.5 padding
design. Prefer \s-1RSA_PKCS1_OAEP_PADDING.\s0
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1SSL, PKCS\s0 #1 v2.0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBERR_get_error\fR\|(3), \fBRAND_bytes\fR\|(3),
\&\fBRSA_size\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-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>.
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