That's the usual confusion of "signing is like encrypting with
your private key". Just forget it. It is a terrible explanation
which does not work. It just seemed to work in days of yore,
when the very first digital signature algorithm (based on
asymmetric cryptography) was first described (I am talking about
RSA and it was in the Disco era); but even for RSA it is not
correct since it fails to take into account padding, which is
critical for security. Have a look at PKCS#1 to see how RSA is
used. In particular, when encrypting data with RSA and a
1024-bit key, the most you can encrypt in one go is 117 bytes,
but the encryption result is always 128 bytes, and that's what a
decryption engine expects. Regardless of how much you try, 128
bytes will not fit in less than 117 bytes... What must be
remembered is that a private key is what is used to do something
that should not be doable by everybody. This means data
decryption (anybody can encrypt a message to Bob, but only Bob
should bee able to read it) and signa