[openssl-users] RSA Digital Signing

[Viktor Dukhovni]

> On Jan 27, 2019, at 12:43 PM, prithiraj das <prithiraj.das at gmail.com> wrote:
> 
> Using OpenSSL, I need to implement digital signing. My approach as of now is:
> 1)  At the sender side, generate the hash of the data using sha256.
> 2)  Encrypt the hash of the data using RSA Private key for the purpose of signing. Send this encrypted hash and the data from Step 1 to the receiverr side.
> 3)  At the receiver's end, Decrypt the signed data(encrypted hash) using the corresponding RSA Public key.
> 4)  Generate hash of the data and verify the decrypted content against this hash to verify the signature
> 
> I was thinking of using RSA_private_encrypt() method to do the signing and RSA_public_decrypt() method to decrypt the signed hash using the corresponding RSA public key. Would the above be a bad approach especially when it comes to using the methods mentioned ? Please recommend the methods to be used that would be better for the purpose of digital signing and verification using sha256 and RSA keys

Do not invent your own RSA-based signature scheme.  Use a standard
RSA signature primitive.  Either RSA-PSS, or PKCS#1 v1.5

   https://en.wikipedia.org/wiki/PKCS_1#Schemes

Typically, you would use CMS, which handles all the details internally.

   https://www.openssl.org/docs/man1.1.0/apps/cms.html

-- 
	Viktor.