/usr/man/cat.1/rsautl.1

RSAUTL(1)                    OpenSSL                    RSAUTL(1)

NAME

     openssl-rsautl, rsautl - RSA utility

SYNOPSIS

     openssl rsautl [-in file] [-out file] [-inkey file] [-pubin]
     [-certin] [-sign] [-verify] [-encrypt] [-decrypt] [-pkcs]
     [-ssl] [-raw] [-hexdump] [-asn1parse]

DESCRIPTION

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

COMMAND OPTIONS

     -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.

     -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 and 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.

     -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.

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RSAUTL(1)                    OpenSSL                    RSAUTL(1)

     -asn1parse
         asn1parse the 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

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RSAUTL(1)                    OpenSSL                    RSAUTL(1)

         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.

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RSAUTL(1)                    OpenSSL                    RSAUTL(1)

SEE ALSO

     dgst(1), rsa(1), genrsa(1)

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See also openssl-rsautl(1)