OPENSSL-RSAUTL(1ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

👑 OPENSSL-RSAUTL(1ossl) — the RSA command 👑

okay bestie, welcome to the OPENSSL-RSAUTL(1ossl) manual page 💖 this is the RSA command, and yes, it’s giving “legacy icon” because it’s deprecated — the page literally says: this command has been deprecated. The openssl-pkeyutl(1) command should be used instead. 🚨

✨ NAME ✨

openssl-rsautl — RSA command 🦋

🌸 SYNOPSIS 🌸

openssl rsautl [-help] [-in file] [-passin arg] [-rev] [-out file]
[-inkey filename|uri] [-keyform DER|PEM|P12|ENGINE] [-pubin] [-certin]
[-sign] [-verify] [-encrypt] [-decrypt] [-pkcs] [-x931] [-oaep] [-raw]
[-hexdump] [-asn1parse] [-engine id] [-rand files] [-writerand file]
[-provider name] [-provider-path path] [-provparam [name:]key=value]
[-propquery propq]

💅 DESCRIPTION 💅

So this command is deprecated — openssl-pkeyutl(1) is the one you should use instead. Periodt. 💀

That said, this command can be used to sign, verify, encrypt and decrypt data using the RSA algorithm. It’s literally in the name, bestie: RSA utility. 🎀

✨ OPTIONS ✨

  • -help — prints out a usage message. cute and useful 🫶
  • -in filename — specifies the input filename to read data from, or standard input if this option is not specified.
  • -passin arg — the passphrase used in the output file. The page says “See see openssl-passphrase-options(1)” — yes, “see see” is literally in there 😭 — so go check openssl-passphrase-options(1).
  • -rev — reverses the order of the input. iconique little flip 🔁
  • -out filename — specifies the output filename to write to, or standard output by default.
  • -inkey filename|uri — the input key; by default it should be an RSA private key. 🔑
  • -keyform DER|PEM|P12|ENGINE — the key format; unspecified by default. See openssl-format-options(1) for details.
  • -pubin — by default a private key is read from the key input. With this option a public key is read instead. If the input contains no public key but a private key, its public part is used. main character public-key energy ✨
  • -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. slay, but keep it private 🔐
  • -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 — PKCS#1 v1.5 padding — and this is the default.
  • -oaep — PKCS#1 OAEP padding.
  • -x931 — ANSI X9.31 padding.
  • -raw — no padding.
bestie, for signatures, only -pkcs and -raw can be used. no cap.
⚠️ Note: because of protection against Bleichenbacher attacks, decryption using PKCS#1 v1.5 mode will not return errors in case padding check failed. Use -raw and inspect the returned value manually to check if the padding is correct. this is one of those “read the fine print or perish” moments 💀
  • -hexdump — hex dump the output data. it’s giving hexadecimal fairy dust 🌈
  • -asn1parse — parse the ASN.1 output data; this is useful when combined with the -verify option.
  • -engine id — see “Engine Options” in openssl(1). This option is deprecated.
  • -rand files — see “Random State Options” in openssl(1) for details.
  • -writerand file — see “Random State Options” in openssl(1) for details.
  • -provider name — see “Provider Options” in openssl(1), provider(7), and property(7).
  • -provider-path path — see “Provider Options” in openssl(1), provider(7), and property(7).
  • -provparam [name:]key=value — see “Provider Options” in openssl(1), provider(7), and property(7).
  • -propquery propq — see “Provider Options” in openssl(1), provider(7), and property(7).

🦋 NOTES 🦋

Since this command uses the RSA algorithm directly, it can only be used to sign or verify small pieces of data. tiny data only, bestie — it’s not built for a whole vibe archive 😭

🎀 EXAMPLES 🎀

Examples equivalent to these can be found in the documentation for the non-deprecated openssl-pkeyutl(1) command.

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. look at those 0xff bytes go 🔥

It is possible to analyse the signature of certificates using this command in conjunction with openssl-asn1parse(1). Consider the self signed example in certs/pca-cert.pem. Running openssl-asn1parse(1) 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. ate and left no crumbs 💅

💜 SEE ALSO 💜

🌈 HISTORY 🌈

  • This command was deprecated in OpenSSL 3.0.
  • The -engine option was deprecated in OpenSSL 3.0.
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.

okay bestie that’s the whole page 💖 this was OPENSSL-RSAUTL(1ossl) from OpenSSL 3.5.6, dated 2026-04-07 — mwah, go forth and use openssl-pkeyutl(1) instead 😘✨

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