rsautl(1ssl) — Commands

NAME

rsautl − RSA utility

SYNOPSIS

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

OPTIONS

−infilename
Specifies the input filename to read data from or standard input if this option is not specified.

−outfilename
Specifies the output filename to write to or standard output by default.

−inkey−file
Input key file. By default it should be an RSA private key.

−pubinThe input file is an RSA public key.

−certinThe input is a certificate containing an RSA public key.

−signSigns the input data and outputs the signed result. This requires and RSA private key.

−verifyVerifies 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.

−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 dumps the output data.

−asn1parse
Asn1parses the output data. This is useful when combined with the −verify option.

DESCRIPTION

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

NOTES

Because rsautl uses the RSA algorithm directly, it 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 file -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 analyze the signature of certificates using this utility in conjunction with asn1parse. Consider the self-signed example in certs/pca-cert.pem. Running asn1parse yields the following:

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 using the following command:

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

The certificate public key can be extracted using the following command:

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

The signature can be analyzed 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. The digest used was md5. The part of the certificate that was signed can be extracted with the following command:

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

Its digest can be computed with the following command:

openssl md5 -c tbs
MD5(tbs)= f3:46:9e:aa:1a:4a:73:c9:37:ea:93:00:48:25:08:b5

This agrees with the recovered value above.

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