114 Indirect re-encryption scheme for sender and recipient anonymity MIX 1 MIX 2 MIX 3 MIX 4 MIX 5 S R unobservable transfer c5 k5c4 k4cs ksc5 k5c4 k4cs ks d 4 k 4 ds ksds ks d 5 k 5 ksk4k5ksk4k5 d 2 k 2 d 3 k 3 d 1 k 1 1 5 3 4 6 8 7 9 7 8 encryption observable transfer decryption message header message content k4k4 k5k5 c 3 k 3 c 2 k 2 c 1 k 1 ksk3k2k1ksk3k2k1 k2k2 k3k3 k1k1 4 6 5 3 for sender anonymityfor recipient anonymity 2 3 rd party, to hold the anonymous return addresses for anonymous query delivery using sender anonymity scheme pickup using recipient anonymity scheme, initiated using sender anonymity scheme