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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 RSA_PKCS1_PADDING 4
.IX Item "RSA_PKCS1_PADDING"
PKCS #1 v1.5 padding. This currently is the most widely used mode.
.IP RSA_PKCS1_OAEP_PADDING 4
.IX Item "RSA_PKCS1_OAEP_PADDING"
EME-OAEP as defined in PKCS #1 v2.0 with SHA\-1, MGF1 and an empty
encoding parameter. This mode is recommended for all new applications.
.IP RSA_SSLV23_PADDING 4
.IX Item "RSA_SSLV23_PADDING"
PKCS #1 v1.5 padding with an SSL-specific modification that denotes
that the server is SSL3 capable.
.IP RSA_NO_PADDING 4
.IX Item "RSA_NO_PADDING"
Raw RSA encryption. This mode should \fIonly\fR be used to implement
cryptographically sound padding modes in the application code.
Encrypting user data directly with RSA is insecure.
.PP
\&\fBflen\fR must be less than RSA_size(\fBrsa\fR) \- 11 for the PKCS #1 v1.5
based padding modes, less than RSA_size(\fBrsa\fR) \- 41 for
RSA_PKCS1_OAEP_PADDING and exactly RSA_size(\fBrsa\fR) for RSA_NO_PADDING.
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 RSA_PKCS1_PADDING mode leak information
which can potentially be used to mount a Bleichenbacher padding oracle
attack. This is an inherent weakness in the PKCS #1 v1.5 padding
design. Prefer RSA_PKCS1_OAEP_PADDING.
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
SSL, PKCS #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. RSA_NO_PADDING is
available since SSLeay 0.9.0, OAEP was added in OpenSSL 0.9.2b.