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command-lineubuntuopenssldigital-signature

openssl command line to verify the signature

Hi I have generated a key pair and used the private key to generate a signature.

openssl rsautl -sign -in helloworld.txt -inkey aa.pem -out sig

However I am unable to verify the signature with my public key:

openssl rsautl -verify -in helloworld.txt -inkey aa.pub -sigfile sig

I know there -sigfile is deprecated. and some of the online doc from openssl.org is wrong.

Whats the command I should use to verify the sig with my public key?

Solution

  • I found two solutions to your problem.

    You can use rsautl this way: (with private key: my.key and public key my-pub.pem)

    $ openssl rsautl -sign -inkey my.key -out in.txt.rsa -in in.txt
Enter pass phrase for my.key:
$ openssl rsautl -verify -inkey my-pub.pem -in in.txt.rsa -pubin
Bonjour

    With this method, the whole document is included within the signature file and is output by the final command.

    But in my case, my certificate says: Signature Algorithm: sha1WithRSAEncryption. So I would recommend that you use the standard way of signing documents in 4 steps: (This method is used for all asymmetric electronic signatures in order not to overload the signature file and/or CPU usage)

    1. Create digest of document to sign (sender)
    2. Sign digest with private key (sender)
    3. Create digest of document to verify (recipient)
    4. Verify signature with public key (recipient)

    OpenSSL does this in two steps:

    $ openssl dgst -sha256 -sign my.key -out in.txt.sha256 in.txt 
Enter pass phrase for my.key:
$ openssl dgst -sha256 -verify my-pub.pem -signature in.txt.sha256 in.txt  
Verified OK

    With this method, you send the recipient two documents: the original file plain text, the signature file signed digest. Attention: the signature file does not include the whole document! Only the digest.