OPENSSL-RSAUTL(1ossl)

📦
version 3.5.9 · 8 versions
, in alpine 3.23, alpine 3.24

💅 OPENSSL-RSAUTL(1ossl) — the RSA command, bestie edition 🎀

okay so first things first: this is openssl-rsautl, an OpenSSL command, and it's the RSA one. That's the whole vibe. ✨

💖 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 🌸

Bestie, I have to be the one to tell you: this command has been deprecated. You're supposed to use openssl-pkeyutl(1) instead, okay? Like, that's the main character now. 😭

But for the record, what this one does is sign, verify, encrypt and decrypt data using the RSA algorithm. That's the whole gig. 💅

✨ OPTIONS ✨

  • -help — prints out a usage message. Cute little "here's how you use me" moment. 🫶
  • -in filename — tells it which input filename to read data from. No option given? It just reads standard input, nbd.
  • -passin arg — the passphrase used in the output file. See openssl-passphrase-options(1). (yes, the original really does say "see see" — I'm not fixing it, I'm just reporting the news 💀)
  • -rev — reverses the order of the input. Backwards slay.
  • -out filename — the output filename to write to. Default is standard output, obvs.
  • -inkey filename|uri — the input key. By default it should be an RSA private key, fyi.
  • -keyform DER|PEM|P12|ENGINE — the key format. Unspecified by default. See openssl-format-options(1) for the details, iykyk.
  • -pubin — so by default a private key gets read from the key input. With this option, a public key gets read instead. And if the input has no public key but does have a private key, then its public part is used. flexible icon behavior. ✨
  • -certin — the input is a certificate containing an RSA public key. 🎀
  • -sign — signs the input data and outputs the signed result. This one requires an RSA private key, no cap.
  • -verify — verifies the input data and outputs 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, -x931, -raw — the padding to use, respectively: PKCS#1 v1.5 (that's the default), PKCS#1 OAEP, ANSI X9.31, or no padding at all. For signatures, only -pkcs and -raw can be used. 😤
Note, and this one's important: because of protection against Bleichenbacher attacks, decryption using PKCS#1 v1.5 mode will not return errors in case the padding check failed. So if you actually wanna check whether the padding is correct, use -raw and inspect the returned value manually. Like, with your own eyeballs. 👀
  • -hexdump — hex dumps the output data. Very "let me see the raw truth of it" of it.
  • -asn1parse — parses the ASN.1 output data. Super useful when you combine it with the -verify option. 🧚
  • -engine id — see "Engine Options" in openssl(1). Heads up: this option is deprecated.
  • -rand files, -writerand file — see "Random State Options" in openssl(1) for the deets.
  • -provider name, -provider-path path, -provparam [name:]key=value, -propquery propq — see "Provider Options" in openssl(1), provider(7), and property(7).

🦋 NOTES 🦋

Because this command uses the RSA algorithm directly, it can only be used to sign or verify small pieces of data. Like, small small. Don't come at it with a whole video file, bestie. 🙈

⭐ EXAMPLES ⭐

Examples equivalent to these can be found in the documentation for the non-deprecated openssl-pkeyutl(1) command. (go check that one out too, it's giving successor energy 👑)

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. So like, different bytes, different story. 💅

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. slay, the math checks out. 🔥

🌈 SEE ALSO 🌈

openssl(1), openssl-pkeyutl(1), openssl-dgst(1), openssl-rsa(1), openssl-genrsa(1)

💜 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 that's the whole page, bestie 💖 written by the OpenSSL crew, version 3.5.9, dated 2026-09-29, and this manual page goes by OPENSSL-RSAUTL(1ossl). go forth and use openssl-pkeyutl(1) like the responsible icon you are 👑✨

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