Chosen Message Attack The attacker tries to find a pair(m,s )from several pairs of signature (mi, Si)and the public key MS) Chosen Message public key pair of message Attacker and signature (d: secret key messages m Sa(m): signatures Signing oracle If the attacker can choose new messages dependent to obtained signatures is called the adaptive chosen message attack 1818 Chosen Message Attack The attacker tries to find a pair (m,s) from several pairs of signature (mi ,si ) and the public key. Chosen Message Attacker public key (m,s): pair of message and signature. (d: secret key ) Signing Oracle messages m Sd (m): signatures If the attacker can choose new messages dependent to obtained signatures, it is called the adaptive chosen message attack