This is how I understand digital signature verification to work in general:
- Plaintext gets run through a hashing mechanism to make a message digest (IBM's terminology, there appear to be plenty of other terms for the hashed data).
- Message digest is encrypted using sender's private key.
- Both encrypted message digest and plaintext are sent to recipient.
- Recipient decrypts message digest using sender's public key.
- Plaintext gets run through hashing mechanism to make message digest, as in step 1.
- If hashed plaintext and decrypted message digest are equivalent, test passes.
What I can't figure out is how this process is specifically applied in RSA verification of a digital certificate. I can't find the plaintext! If it's generated at random for each request, then what's the point of having a digital signature from the assigning CA in the certificate? If it isn't, then where does whoever is verifying the certificate get the plaintext to compare the signature to? I don't see that it's part of the certificate.
So, first, do I understand the general signature verification process as it applies to digital certificate verification? And if I do, can someone solve the "mystery of the missing plaintext" for me?