signature - Generating, Signing and Verifying Digital Certificates - Ask Ubuntu

so here's question project.

in task, use openssl generate digital signatures. please prepare file (example.txt) of size. prepare rsa public/private key pair. following:  1.  sign sha256 hash of example.txt; save output in example.sha256. 2.  verify digital signature in example.sha256. 3.  modify example.txt, , verify digital signature again.  please describe how performed above 3 operations (e.g., exact commands used, etc.). describe observed , explain observations. please explain why digital signatures useful in general. 

so, following.

1.create private/public key pair

openssl genrsa -out private.pem 1024 

2. extracting public key.

openssl rsa -in private.pem -out public.pem -outform pem -pubout 

3. create hash of data.

echo 'data sign' > example.txt  openssl dgst -sha256 < example.txt > hash 

4. sign hash using private key file called example.sha256

openssl rsautl -sign -inkey private.pem -keyform pem -in hash  > example.sha256 

5. verify file (example.txt)and digital signature (example.sha256)

openssl dgst -sha256 -verify public.pem -signature example.sha256 example.txt 

after doing this, error message saying "verification failure"

please correct me if went wrong somewhere.

 generating private/public key pair. 1. openssl genrsa -out private.pem 1024 2. openssl rsa -in private.pem -out public.pem -outform pem -pubout   sign. openssl dgst -sha256 -sign private.pem -out sla.txt.sha256 sla.txt   verify openssl dgst -sha256 -verify public.pem -signature sla.txt.sha256 sla.txt