=pod

=head1 NAME

openssl-rsautl,

rsautl - RSA utility

=head1 SYNOPSIS

B<openssl> B<rsautl>

[B<-help>]

[B<-in file>]

[B<-out file>]

[B<-inkey file>]

[B<-keyform PEM|DER|ENGINE>]

[B<-pubin>]

[B<-certin>]

[B<-sign>]

[B<-verify>]

[B<-encrypt>]

[B<-decrypt>]

[B<-rand file...>]

[B<-writerand file>]

[B<-pkcs>]

[B<-ssl>]

[B<-raw>]

[B<-hexdump>]

[B<-asn1parse>]

=head1 DESCRIPTION

The B<rsautl> command can be used to sign, verify, encrypt and decrypt

data using the RSA algorithm.

=head1 OPTIONS

=over 4

=item B<-help>

Print out a usage message.

=item B<-in filename>

This specifies the input filename to read data from or standard input

if this option is not specified.

=item B<-out filename>

Specifies the output filename to write to or standard output by

default.

=item B<-inkey file>

The input key file, by default it should be an RSA private key.

=item B<-keyform PEM|DER|ENGINE>

The key format PEM, DER or ENGINE.

=item B<-pubin>

The input file is an RSA public key.

=item B<-certin>

The input is a certificate containing an RSA public key.

=item B<-sign>

Sign the input data and output the signed result. This requires

an RSA private key.

=item B<-verify>

Verify the input data and output the recovered data.

=item B<-encrypt>

Encrypt the input data using an RSA public key.

=item B<-decrypt>

Decrypt the input data using an RSA private key.

=item B<-rand file...>

A file or files containing random data used to seed the random number

generator.

Multiple files can be specified separated by an OS-dependent character.

The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for

all others.

=item [B<-writerand file>]

Writes random data to the specified I<file> upon exit.

This can be used with a subsequent B<-rand> flag.

=item B<-pkcs, -oaep, -ssl, -raw>

The padding to use: PKCS#1 v1.5 (the default), PKCS#1 OAEP,

special padding used in SSL v2 backwards compatible handshakes,

or no padding, respectively.

For signatures, only B<-pkcs> and B<-raw> can be used.

=item B<-hexdump>

Hex dump the output data.

=item B<-asn1parse>

Parse the ASN.1 output data, this is useful when combined with the

B<-verify> option.

=back

=head1 NOTES

B<rsautl> because it uses the RSA algorithm directly can only be

used to sign or verify small pieces of data.

=head1 EXAMPLES

Sign some data using a private key:

 openssl rsautl -sign -in file -inkey key.pem -out sig

Recover the signed data

 openssl rsautl -verify -in sig -inkey key.pem

Examine the raw signed data:

 openssl rsautl -verify -in sig -inkey key.pem -raw -hexdump

 0000 - 00 01 ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0010 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0020 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0030 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0040 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0050 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0060 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff   ................

 0070 - ff ff ff ff 00 68 65 6c-6c 6f 20 77 6f 72 6c 64   .....hello world

The PKCS#1 block formatting is evident from this. If this was done using

encrypt and decrypt the block would have been of type 2 (the second byte)

and random padding data visible instead of the 0xff bytes.

It is possible to analyse the signature of certificates using this

utility in conjunction with B<asn1parse>. Consider the self signed

example in certs/pca-cert.pem . Running B<asn1parse> as follows yields:

 openssl asn1parse -in pca-cert.pem

    0:d=0  hl=4 l= 742 cons: SEQUENCE

    4:d=1  hl=4 l= 591 cons:  SEQUENCE

    8:d=2  hl=2 l=   3 cons:   cont [ 0 ]

   10:d=3  hl=2 l=   1 prim:    INTEGER           :02

   13:d=2  hl=2 l=   1 prim:   INTEGER           :00

   16:d=2  hl=2 l=  13 cons:   SEQUENCE

   18:d=3  hl=2 l=   9 prim:    OBJECT            :md5WithRSAEncryption

   29:d=3  hl=2 l=   0 prim:    NULL

   31:d=2  hl=2 l=  92 cons:   SEQUENCE

   33:d=3  hl=2 l=  11 cons:    SET

   35:d=4  hl=2 l=   9 cons:     SEQUENCE

   37:d=5  hl=2 l=   3 prim:      OBJECT            :countryName

   42:d=5  hl=2 l=   2 prim:      PRINTABLESTRING   :AU

  ....

  599:d=1  hl=2 l=  13 cons:  SEQUENCE

  601:d=2  hl=2 l=   9 prim:   OBJECT            :md5WithRSAEncryption

  612:d=2  hl=2 l=   0 prim:   NULL

  614:d=1  hl=3 l= 129 prim:  BIT STRING

The final BIT STRING contains the actual signature. It can be extracted with:

 openssl asn1parse -in pca-cert.pem -out sig -noout -strparse 614

The certificate public key can be extracted with:

 openssl x509 -in test/testx509.pem -pubkey -noout >pubkey.pem

The signature can be analysed with:

 openssl rsautl -in sig -verify -asn1parse -inkey pubkey.pem -pubin

    0:d=0  hl=2 l=  32 cons: SEQUENCE

    2:d=1  hl=2 l=  12 cons:  SEQUENCE

    4:d=2  hl=2 l=   8 prim:   OBJECT            :md5

   14:d=2  hl=2 l=   0 prim:   NULL

   16:d=1  hl=2 l=  16 prim:  OCTET STRING

      0000 - f3 46 9e aa 1a 4a 73 c9-37 ea 93 00 48 25 08 b5   .F...Js.7...H%..

This is the parsed version of an ASN1 DigestInfo structure. It can be seen that

the digest used was md5. The actual part of the certificate that was signed can

be extracted with:

 openssl asn1parse -in pca-cert.pem -out tbs -noout -strparse 4

and its digest computed with:

 openssl md5 -c tbs

 MD5(tbs)= f3:46:9e:aa:1a:4a:73:c9:37:ea:93:00:48:25:08:b5

which it can be seen agrees with the recovered value above.

=head1 SEE ALSO

L<dgst(1)>, L<rsa(1)>, L<genrsa(1)>

=head1 COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.

=cut