When Symmetrically encrypting a file, (not signing, not an asymmetric encryption question), is it possible to conceal the encryption algorithm used, or is it already concealed, but just showing on systems as a result of being cached somehow?
Analogy: When signing an encrypted file, it is possible to conceal the recipient ID. But how do you conceal the encryption algorithm used when using Symmetrical encryption using GnuPG, (gpg4win, in this case)?
gpg --armor --symmetric --cipher-algo AES256 --output encryptedOutputFile.asc unencryptedInputFile.txt
gpg --decrypt plaintextfile.txt
gpg: AES256 Encrypted Data
gpg: encrypted with 1 passphrase
Somehow, gpg4win is using Space Magic to infer what the symmetric algorithm is even before the passphrase is entered. How is this occurring? I tried to eliminate the possibility of the algorithm being present in the cache, but it still is being inferred. GPG uses CAST5 by default, so how is it inferring AES256?
So, how is GPG inferring that AES256 is used, even before the passphrase is specified?
Is there any way to conceal the algorithm used with a gpg -- flag?