AES is only defined for 128, 192, or 256 bit keys. You'd need to switch to a different block cipher like Blowfish (up to 448 bit keys), RC2 (up to 1024 bit keys

AES is only defined for 128, 192, or 256 bit keys. You'd need to switch to a different block cipher like Blowfish (up to 448 bit keys), RC2 (up to 1024 bit keys), or RC5 (up to 2048 bit keys) to have a larger keyspace.