.\"	$OpenBSD: RSA_sign.3,v 1.6 2018/03/27 17:35:50 schwarze Exp $
.\"	OpenSSL aa90ca11 Aug 20 15:48:56 2016 -0400
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.Dd $Mdocdate: March 27 2018 $
.Dt RSA_SIGN 3
.Os
.Sh NAME
.Nm RSA_sign ,
.Nm RSA_verify
.Nd RSA signatures
.Sh SYNOPSIS
.In openssl/rsa.h
.Ft int
.Fo RSA_sign
.Fa "int type"
.Fa "const unsigned char *m"
.Fa "unsigned int m_len"
.Fa "unsigned char *sigret"
.Fa "unsigned int *siglen"
.Fa "RSA *rsa"
.Fc
.Ft int
.Fo RSA_verify
.Fa "int type"
.Fa "const unsigned char *m"
.Fa "unsigned int m_len"
.Fa "unsigned char *sigbuf"
.Fa "unsigned int siglen"
.Fa "RSA *rsa"
.Fc
.Sh DESCRIPTION
.Fn RSA_sign
signs the message digest
.Fa m
of size
.Fa m_len
using the private key
.Fa rsa
using RSASSA-PKCS1-v1_5 as specified in RFC 3447.
It stores the signature in
.Fa sigret
and the signature size in
.Fa siglen .
.Fa sigret
must point to
.Fn RSA_size rsa
bytes of memory.
Note that PKCS #1 adds meta-data, placing limits on the size of the key
that can be used.
See
.Xr RSA_private_encrypt 3
for lower-level operations.
.Pp
.Fa type
denotes the message digest algorithm that was used to generate
.Fa m .
If
.Fa type
is
.Sy NID_md5_sha1 ,
an SSL signature (MD5 and SHA1 message digests with PKCS #1 padding and
no algorithm identifier) is created.
.Pp
.Fn RSA_verify
verifies that the signature
.Fa sigbuf
of size
.Fa siglen
matches a given message digest
.Fa m
of size
.Fa m_len .
.Fa type
denotes the message digest algorithm that was used to generate the
signature.
.Fa rsa
is the signer's public key.
.Sh RETURN VALUES
.Fn RSA_sign
returns 1 on success.
.Fn RSA_verify
returns 1 on successful verification.
.Pp
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr ERR_get_error 3 ,
.Xr RSA_new 3 ,
.Xr RSA_private_encrypt 3 ,
.Xr RSA_public_decrypt 3
.Sh STANDARDS
SSL, PKCS #1 v2.0
.Sh HISTORY
.Fn RSA_sign
first appeared in SSLeay 0.4.4.
.Fn RSA_verify
first appeared in SSLeay 0.6.0.
Both functions have been available since
.Ox 2.4 .