RSAUTL(1) OpenSSL RSAUTL(1) NNAAMMEE openssl-rsautl, rsautl - RSA utility SSYYNNOOPPSSIISS ooppeennssssll rrssaauuttll [--iinn ffiillee] [--oouutt ffiillee] [--iinnkkeeyy ffiillee] [--ppuubbiinn] [--cceerrttiinn] [--ssiiggnn] [--vveerriiffyy] [--eennccrryypptt] [--ddeeccrryypptt] [--ppkkccss] [--ssssll] [--rraaww] [--hheexx-- dduummpp] [--aassnn11ppaarrssee] DDEESSCCRRIIPPTTIIOONN The rrssaauuttll command can be used to sign, verify, encrypt and decrypt data using the RSA algorithm. CCOOMMMMAANNDD OOPPTTIIOONNSS --iinn ffiilleennaammee This specifies the input filename to read data from or standard input if this option is not specified. --oouutt ffiilleennaammee specifies the output filename to write to or standard output by default. --iinnkkeeyy ffiillee the input key file, by default it should be an RSA private key. --ppuubbiinn the input file is an RSA public key. --cceerrttiinn the input is a certificate containing an RSA public key. --ssiiggnn sign the input data and output the signed result. This requires and RSA private key. --vveerriiffyy verify the input data and output the recovered data. --eennccrryypptt encrypt the input data using an RSA public key. --ddeeccrryypptt decrypt the input data using an RSA private key. --ppkkccss,, --ooaaeepp,, --ssssll,, --rraaww the padding to use: PKCS#1 v1.5 (the default), PKCS#1 OAEP, special padding used in SSL v2 backwards compatible handshakes, or no pad- ding, respectively. For signatures, only --ppkkccss and --rraaww can be used. --hheexxdduummpp hex dump the output data. --aassnn11ppaarrssee asn1parse the output data, this is useful when combined with the --vveerriiffyy option. NNOOTTEESS rrssaauuttll because it uses the RSA algorithm directly can only be used to sign or verify small pieces of data. EEXXAAMMPPLLEESS 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 sec- ond 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 aassnn11ppaarrssee. Consider the self signed example in certs/pca-cert.pem . Running aassnn11ppaarrssee 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. SSEEEE AALLSSOO _d_g_s_t(1), _r_s_a(1), _g_e_n_r_s_a(1) 1.0.2u 2019-12-20 RSAUTL(1)