# Digital signatures under plain RSA

Show that digital signatures under plain RSA are insecure (Plain RSA means that signing is done by calculating $m^d\bmod n$, with $0\le m<n$, and no padding or hashing of $m$).

Write an algorithm that, given someone’s public signature verification key ($e$, $n$), can easily generate a (message, signature) pair for some message that the private key holder never intended to sign. For full credit your algorithm should not require a signing oracle and your algorithm should generate “signed” messages where your message is different than its signature (Hints: The message need not have any meaning to count as a forgery. Think backwards).

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We rather expect you to do your own homework. What have you tried? –  poncho Feb 18 '14 at 3:43
This is, in fact, answered in another related question of the forum. You just need to work a little and look for it. Posting your homework without even explaining which are your doubts is not fair. –  izaera Feb 18 '14 at 7:42
Here it is: crypto.stackexchange.com/questions/2474/… –  izaera Feb 18 '14 at 8:19