For AES you have to search the entire keyspace, but for RSA ( and AFAIK any public key scheme) you can actually calculate the private key. The security of publi

For AES you have to search the entire keyspace, but for RSA ( and AFAIK any public key scheme) you can actually calculate the private key. The security of public key cryptography relies therefore on one-way functions, which are easy to calculate in one direction but very hard to calculate in the other direction. ( This is used to generate the public and private keys together, but the inverse operation, breaking the encryption, should be prohibitively hard to calculate in practice.) Because of this you can not really compare key length between symmetric and asymmetric encryption schemes.