Here is the context: to transmit FATCA data to US IRS service the IDES protocol defines the following steps
- sign the XML
Payload.xmlfile with enveloping signature, SHA-256 with RSA private key, as
- pack the signed XML
Payload-signed.xmlfile into a zip file
- generate a single-usage 32 bytes key for AES-256
- encrypt the Zip archive
Payload.zipwith AES-256 as
- encrypt the AES with RSA public key for exchange as
- bundle encrypted AES key
Keyand encrypted zip file
Payloadin a Zip archive
Is there any security reason not to encrypt directly
Payload.zipwith RSA public key designed for exchange ?
How to compare security of RSA encryption between a (really small) 32 bytes (the AES key) file and a larger Zip file ?