-help

Print out a usage message.

-in

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

-out

specifies the output filename to write to or standard output by default.

-inkey

the input key file, by default it should be an RSA private key.

-keyform

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.

-pkcs

the padding to use: PKCS#1 v1.5 (the default), PKCS#1 OAEP, special padding used in SSL v2 backwardscompatible handshakes, or no padding, respectively. For signatures, only -pkcs and -raw can be used.

-hexdump

hex dump the output data.

-asn1parse

asn1parse the output data, this is useful when combined with the -verify option.NOTESrsautl because it uses the RSA algorithm directly can only be used to sign or verify small pieces of data.EXAMPLESSign some data using a private key:openssl rsautl -sign -in file -inkey key.pem -out sigRecover the signed dataopenssl rsautl -verify -in sig -inkey key.pemExamine the raw signed data:openssl rsautl -verify -in sig -inkey key.pem -raw -hexdump0000 - 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 worldThe PKCS#1 block formatting is evident from this. If this was done using encrypt and decrypt the block wouldhave 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.pem0:d=0 hl=4 l= 742 cons: SEQUENCE4:d=1 hl=4 l= 591 cons: SEQUENCE8:d=2 hl=2 l= 3 cons: cont [ 0 ]10:d=3 hl=2 l= 1 prim: INTEGER :0213:d=2 hl=2 l= 1 prim: INTEGER :0016:d=2 hl=2 l= 13 cons: SEQUENCE18:d=3 hl=2 l= 9 prim: OBJECT :md5WithRSAEncryption29:d=3 hl=2 l= 0 prim: NULL31:d=2 hl=2 l= 92 cons: SEQUENCE33:d=3 hl=2 l= 11 cons: SET35:d=4 hl=2 l= 9 cons: SEQUENCE37:d=5 hl=2 l= 3 prim: OBJECT :countryName42:d=5 hl=2 l= 2 prim: PRINTABLESTRING :AU....599:d=1 hl=2 l= 13 cons: SEQUENCE601:d=2 hl=2 l= 9 prim: OBJECT :md5WithRSAEncryption612:d=2 hl=2 l= 0 prim: NULL614:d=1 hl=3 l= 129 prim: BIT STRINGThe final BIT STRING contains the actual signature. It can be extracted with:openssl asn1parse -in pca-cert.pem -out sig -noout -strparse 614The certificate public key can be extracted with:openssl x509 -in test/testx509.pem -pubkey -noout >pubkey.pemThe signature can be analysed with:openssl rsautl -in sig -verify -asn1parse -inkey pubkey.pem -pubin0:d=0 hl=2 l= 32 cons: SEQUENCE2:d=1 hl=2 l= 12 cons: SEQUENCE4:d=2 hl=2 l= 8 prim: OBJECT :md514:d=2 hl=2 l= 0 prim: NULL16:d=1 hl=2 l= 16 prim: OCTET STRING0000 - 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. Theactual part of the certificate that was signed can be extracted with:openssl asn1parse -in pca-cert.pem -out tbs -noout -strparse 4and its digest computed with:openssl md5 -c tbsMD5(tbs)= f3:46:9e:aa:1a:4a:73:c9:37:ea:93:00:48:25:08:b5which it can be seen agrees with the recovered value above.