Final answer:
For the transmission of classified materials, an encryption method such as the Advanced Encryption Standard (AES) with a 256-bit key length is typically required, as part of the Secure Classified Information Handling (SCIH) protocols.
Step-by-step explanation:
The type of crypto standard required for the transmission of classified materials is typically a very robust and secure encryption method. For classified information, governments often mandate the use of encryption standards and protocols that have been rigorously tested and approved for sensitive communication. This would commonly be a suite of standards known as Secure Classified Information Handling (SCIH), which encompasses various protocols for different classification levels. The Advanced Encryption Standard (AES) is a widely recognized encryption method that may be utilized in these circumstances, particularly with a 256-bit key length, often considered one of the strongest encryption levels for classified communication.