rsautl

RSAUTL(1SSL)                        OpenSSL                       RSAUTL(1SSL)

NAME
       openssl-rsautl, rsautl - RSA utility

SYNOPSIS
       openssl rsautl [-help] [-in file] [-out file] [-inkey file] [-keyform
       PEM|DER|ENGINE] [-pubin] [-certin] [-sign] [-verify] [-encrypt]
       [-decrypt] [-rand file...]  [-writerand file] [-pkcs] [-ssl] [-raw]
       [-hexdump] [-asn1parse]

DESCRIPTION
       The rsautl command can be used to sign, verify, encrypt and decrypt
       data using the RSA algorithm.

OPTIONS
       -help
           Print out a usage message.

       -in filename
           This specifies the input filename to read data from or standard
           input if this option is not specified.

       -out filename
           Specifies the output filename to write to or standard output by
           default.

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

       -keyform PEM|DER|ENGINE
           The key format PEM, DER or ENGINE.

       -pubin
           The input file is an RSA public key.

       -certin
           The input is a certificate containing an RSA public key.

       -sign
           Sign the input data and output the signed result. This requires an
           RSA private key.

       -verify
           Verify the input data and output the recovered data.

       -encrypt
           Encrypt the input data using an RSA public key.

       -decrypt
           Decrypt the input data using an RSA private key.

       -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 ; for MS-Windows, , for
           OpenVMS, and : for all others.

       [-writerand file]
           Writes random data to the specified file upon exit.  This can be
           used with a subsequent -rand flag.

       -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 -pkcs and -raw can be
           used.

       -hexdump
           Hex dump the output data.

       -asn1parse
           Parse the ASN.1 output data, this is useful when combined with the
           -verify option.

NOTES
       rsautl because it uses the RSA algorithm directly can only be used to
       sign or verify small pieces of data.

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 asn1parse. Consider the self signed example
       in certs/pca-cert.pem . Running 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.

SEE ALSO
       dgst(1), rsa(1), genrsa(1)

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

1.1.1f                            2023-10-10                      RSAUTL(1SSL)