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131 .IX Title "RSA_private_encrypt 3"
132 .TH RSA_private_encrypt 3 "2018-03-27" "1.0.2o" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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138 RSA_private_encrypt, RSA_public_decrypt \- low level signature operations
140 .IX Header "SYNOPSIS"
142 \& #include <openssl/rsa.h>
144 \& int RSA_private_encrypt(int flen, const unsigned char *from,
145 \& unsigned char *to, RSA *rsa, int padding);
147 \& int RSA_public_decrypt(int flen, const unsigned char *from,
148 \& unsigned char *to, RSA *rsa, int padding);
151 .IX Header "DESCRIPTION"
152 These functions handle \s-1RSA\s0 signatures at a low level.
154 \&\fIRSA_private_encrypt()\fR signs the \fBflen\fR bytes at \fBfrom\fR (usually a
155 message digest with an algorithm identifier) using the private key
156 \&\fBrsa\fR and stores the signature in \fBto\fR. \fBto\fR must point to
157 \&\fBRSA_size(rsa)\fR bytes of memory.
159 \&\fBpadding\fR denotes one of the following modes:
160 .IP "\s-1RSA_PKCS1_PADDING\s0" 4
161 .IX Item "RSA_PKCS1_PADDING"
162 \&\s-1PKCS\s0 #1 v1.5 padding. This function does not handle the
163 \&\fBalgorithmIdentifier\fR specified in \s-1PKCS\s0 #1. When generating or
164 verifying \s-1PKCS\s0 #1 signatures, \fIRSA_sign\fR\|(3) and \fIRSA_verify\fR\|(3) should be
166 .IP "\s-1RSA_NO_PADDING\s0" 4
167 .IX Item "RSA_NO_PADDING"
168 Raw \s-1RSA\s0 signature. This mode should \fIonly\fR be used to implement
169 cryptographically sound padding modes in the application code.
170 Signing user data directly with \s-1RSA\s0 is insecure.
172 \&\fIRSA_public_decrypt()\fR recovers the message digest from the \fBflen\fR
173 bytes long signature at \fBfrom\fR using the signer's public key
174 \&\fBrsa\fR. \fBto\fR must point to a memory section large enough to hold the
175 message digest (which is smaller than \fBRSA_size(rsa) \-
176 11\fR). \fBpadding\fR is the padding mode that was used to sign the data.
178 .IX Header "RETURN VALUES"
179 \&\fIRSA_private_encrypt()\fR returns the size of the signature (i.e.,
180 RSA_size(rsa)). \fIRSA_public_decrypt()\fR returns the size of the
181 recovered message digest.
183 On error, \-1 is returned; the error codes can be
184 obtained by \fIERR_get_error\fR\|(3).
186 .IX Header "SEE ALSO"
187 \&\fIERR_get_error\fR\|(3), \fIrsa\fR\|(3),
188 \&\fIRSA_sign\fR\|(3), \fIRSA_verify\fR\|(3)
191 The \fBpadding\fR argument was added in SSLeay 0.8. \s-1RSA_NO_PADDING\s0 is
192 available since SSLeay 0.9.0.