rsautl(1)
RSAUTL(1) 0.9.6h (2001-04-25) RSAUTL(1)
NAME
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) 0.9.6h (2001-04-25) 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 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 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) 0.9.6h (2001-04-25) 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 -pubout -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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SEE ALSO
dgst(1), rsa(1), genrsa(1)
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