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.\"
.IX Title "RSA_public_encrypt 3"
.TH RSA_public_encrypt 3 "2019-12-20" "1.0.2u" "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.
.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 be less than RSA_size(\fBrsa\fR) \- 11 for the \s-1PKCS\s0 #1 v1.5
based padding modes, less than RSA_size(\fBrsa\fR) \- 41 for
\&\s-1RSA_PKCS1_OAEP_PADDING\s0 and exactly RSA_size(\fBrsa\fR) for \s-1RSA_NO_PADDING.\s0
The random number generator must be seeded prior to calling
\&\fBRSA_public_encrypt()\fR.
.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. \fBto\fR must point
to a memory section large enough to hold the decrypted data (which is
smaller than RSA_size(\fBrsa\fR)). \fBpadding\fR is the padding mode that
was used to encrypt the data.
.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.
.PP
On error, \-1 is returned; the error codes can be
obtained by \fBERR_get_error\fR\|(3).
.SH "WARNING"
.IX Header "WARNING"
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\fR\|(3), \fBrsa\fR\|(3),
\&\fBRSA_size\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, \s-1OAEP\s0 was added in OpenSSL 0.9.2b.
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