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.\"
.IX Title "RSA_padding_add_PKCS1_type_1 3"
.TH RSA_padding_add_PKCS1_type_1 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.
.if n .ad l
.nh
.SH NAME
RSA_padding_add_PKCS1_type_1, RSA_padding_check_PKCS1_type_1,
RSA_padding_add_PKCS1_type_2, RSA_padding_check_PKCS1_type_2,
RSA_padding_add_PKCS1_OAEP, RSA_padding_check_PKCS1_OAEP,
RSA_padding_add_SSLv23, RSA_padding_check_SSLv23,
RSA_padding_add_none, RSA_padding_check_none \- asymmetric encryption
padding
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rsa.h>
\&
\& int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
\&    unsigned char *f, int fl);
\&
\& int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
\&    unsigned char *f, int fl, int rsa_len);
\&
\& int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
\&    unsigned char *f, int fl);
\&
\& int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
\&    unsigned char *f, int fl, int rsa_len);
\&
\& int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
\&    unsigned char *f, int fl, unsigned char *p, int pl);
\&
\& int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
\&    unsigned char *f, int fl, int rsa_len, unsigned char *p, int pl);
\&
\& int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
\&    unsigned char *f, int fl);
\&
\& int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
\&    unsigned char *f, int fl, int rsa_len);
\&
\& int RSA_padding_add_none(unsigned char *to, int tlen,
\&    unsigned char *f, int fl);
\&
\& int RSA_padding_check_none(unsigned char *to, int tlen,
\&    unsigned char *f, int fl, int rsa_len);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
The \fBRSA_padding_xxx_xxx()\fR functions are called from the RSA encrypt,
decrypt, sign and verify functions. Normally they should not be called
from application programs.
.PP
However, they can also be called directly to implement padding for other
asymmetric ciphers. \fBRSA_padding_add_PKCS1_OAEP()\fR and
\&\fBRSA_padding_check_PKCS1_OAEP()\fR may be used in an application combined
with \fBRSA_NO_PADDING\fR in order to implement OAEP with an encoding
parameter.
.PP
\&\fBRSA_padding_add_xxx()\fR encodes \fBfl\fR bytes from \fBf\fR so as to fit into
\&\fBtlen\fR bytes and stores the result at \fBto\fR. An error occurs if \fBfl\fR
does not meet the size requirements of the encoding method.
.PP
The following encoding methods are implemented:
.IP PKCS1_type_1 4
.IX Item "PKCS1_type_1"
PKCS #1 v2.0 EMSA\-PKCS1\-v1_5 (PKCS #1 v1.5 block type 1); used for signatures
.IP PKCS1_type_2 4
.IX Item "PKCS1_type_2"
PKCS #1 v2.0 EME\-PKCS1\-v1_5 (PKCS #1 v1.5 block type 2)
.IP PKCS1_OAEP 4
.IX Item "PKCS1_OAEP"
PKCS #1 v2.0 EME-OAEP
.IP SSLv23 4
.IX Item "SSLv23"
PKCS #1 EME\-PKCS1\-v1_5 with SSL-specific modification
.IP none 4
.IX Item "none"
simply copy the data
.PP
The random number generator must be seeded prior to calling
\&\fBRSA_padding_add_xxx()\fR.
.PP
\&\fBRSA_padding_check_xxx()\fR verifies that the \fBfl\fR bytes at \fBf\fR contain
a valid encoding for a \fBrsa_len\fR byte RSA key in the respective
encoding method and stores the recovered data of at most \fBtlen\fR bytes
(for \fBRSA_NO_PADDING\fR: of size \fBtlen\fR)
at \fBto\fR.
.PP
For \fBRSA_padding_xxx_OAEP()\fR, \fBp\fR points to the encoding parameter
of length \fBpl\fR. \fBp\fR may be \fBNULL\fR if \fBpl\fR is 0.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
The \fBRSA_padding_add_xxx()\fR functions return 1 on success, 0 on error.
The \fBRSA_padding_check_xxx()\fR functions return the length of the
recovered data, \-1 on error. Error codes can be obtained by calling
\&\fBERR_get_error\fR\|(3).
.SH WARNING
.IX Header "WARNING"
The \fBRSA_padding_check_PKCS1_type_2()\fR padding check leaks timing
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 PKCS1_OAEP padding. Otherwise it can
be recommended to pass zero-padded \fBf\fR, so that \fBfl\fR equals to
\&\fBrsa_len\fR, and if fixed by protocol, \fBtlen\fR being set to the
expected length. In such case leakage would be minimal, it would
take attacker's ability to observe memory access pattern with byte
granilarity as it occurs, post-factum timing analysis won't do.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBRSA_public_encrypt\fR\|(3),
\&\fBRSA_private_decrypt\fR\|(3),
\&\fBRSA_sign\fR\|(3), \fBRSA_verify\fR\|(3)
.SH HISTORY
.IX Header "HISTORY"
\&\fBRSA_padding_add_PKCS1_type_1()\fR, \fBRSA_padding_check_PKCS1_type_1()\fR,
\&\fBRSA_padding_add_PKCS1_type_2()\fR, \fBRSA_padding_check_PKCS1_type_2()\fR,
\&\fBRSA_padding_add_SSLv23()\fR, \fBRSA_padding_check_SSLv23()\fR,
\&\fBRSA_padding_add_none()\fR and \fBRSA_padding_check_none()\fR appeared in
SSLeay 0.9.0.
.PP
\&\fBRSA_padding_add_PKCS1_OAEP()\fR and \fBRSA_padding_check_PKCS1_OAEP()\fR were
added in OpenSSL 0.9.2b.