openssl command line to verify the signature

Question

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?

Spencerspencerian

your method is correct, I was missing digest part, trying to sign the whole document! Thanks for your help! I also found out some useful links I use it to do the X.509 CA thing: sandbox.rulemaker.net/ngps/m2/howto.ca.html octaldream.com/~scottm/talks/ssl/opensslca.html – Spencerspencerian

Answer 1

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.

Hovercraft

When using this very command line to verify the signature of a given data, I get the following error output : Verification failure\n Error in dgst does this mean the verification failed because of an error or because the files didn't match correctly ? – Limb

There is no real reason for signature decoding to fail, so I'd say mismatch. – Karp

Do you happen to know if the format of the signature is important ? I think the format .sign is not handled – Limb

You should really look at the documentation. Signature files are text files, extensions does not matter. Yes there is a format for the content of the file, but without looking at it, I can't say if it's ok. Test it first with the command I put here and a random text file, it should work, then test your own files. – Karp

Answer 2

Verify using public key:

echo "plop" > "helloworld.txt"
openssl rsautl -sign -in helloworld.txt -inkey private.pem -out sig
openssl rsautl -verify -in sig -inkey public.pem -pubin
> plop

Midkiff

Answer 3

your method is basically correct. What you miss is to tell rsautl that the inut key file file is a public key by add "-pubin". The item "-pubin" OpenSSL rsautl document isn't accurate " -pubin the input file is an RSA public key. " should be " -pubin the input key file is an RSA public key. " Since the input file should be a signature file.

Bethina

Answer 4

You can check the doc for rsautl

In your example, this would give :

openssl rsautl -verify -in sig -inkey aa.pem

I have copied my full history below :

echo "plop" > "helloworld.txt"
openssl rsautl -sign -in helloworld.txt -inkey aa.pem -out sig
openssl rsautl -verify -in sig -inkey aa.pem
> plop

Corporation

Hi, thanks, I did read the manual, But I need to use a public key to verify. not private key. – Spencerspencerian

use -pubin and pass the public key as an argument to -inkey – Fandango