openssl 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: specifies the input file name to read data from or standard input if this option is not specified.
-out filename: specifies the output file name to write to or standard output by default.
-inkey file: specifies the input key file, by default it should be an RSA private key.
-pubin: specifies the input file is an RSA public key.
-keyform PEM|DER|ENGINE: The key format PEM, DER or ENGINE.
-certin: indicates that the input is a certificate containing an RSA public key.
-sign: signs the input data and output the signed result. This requires an RSA private key.
-verify: verifies the input data and output the recovered data.
-encrypt: encrypts the input data using an RSA public key.
-decrypt: decrypts 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: specifies 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 dumps 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.

COPYRIGHT

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 here: OpenSSL.

AVAILABILITY

PTC MKS Toolkit for System Administrators
PTC MKS Toolkit for Developers
PTC MKS Toolkit for Interoperability
PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition

openssl rsautl
RSA utility

openssl command