If --hidden-encrypt-to is used, there still will be signs of that. Specifically, the message addressed to 0x0000000 and the recipient will basically brute force

If --hidden-encrypt-to is used, there still will be signs of that. Specifically, the message addressed to 0x0000000 and the recipient will basically brute force it uses every key he/she has. Having said, that, according to PGP Dump Old: Public-Key Encrypted Session Key Packet(tag 1)(524 bytes) New version(3) Key ID - 0x5B50940B79DEBE35 Pub alg - RSA Encrypt or Sign(pub 1) RSA m^e mod n(4096 bits) - ... -> m = sym alg(1 byte) + checksum(2 bytes) + PKCS-1 block type 02 New: Symmetrically Encrypted and MDC Packet(tag 18)(4096 bytes) partial start Ver 1 Encrypted data [sym alg is specified in pub-key encrypted session key] (plain text + MDC SHA1(20 bytes)) New: (1024 bytes) partial continue New: (18 bytes) partial end It looks like we can merely see that the message is destined to 0x5B50940B79DEBE35. We won't be able to tell who's signer until it is decrypted.