US
RFC 8551: Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification
https://www.rfc-editor.org/rfc/rfc8551
…ion functions for the key wrap and content- encryption algorithms [ RFC3370 ] [ RFC3565 ] and the key sizes for the two algorithms MUST be the same (e.g., AES-128 key wrap algorithm with AES-128 content-encryption algorithm). As both 128-bit and 256-bit AES modes are mandatory to…