Files
darkfi/proof/encrypt.zk
parazyd 6a024ab801 zkas: Add a field definition on top of the circuit file.
Currently unused, but will probably be expanded to define proofs over
different fields.
2023-08-14 17:09:18 +02:00

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# Verifiable encryption inside ZK
# Normally this algo will be hardened due to malleability attacks
# on the ciphertext, but the ZK proof ensures that the ciphertext
# cannot be modified.
#
# This is basically the el gamal scheme in ZK
k = 13;
field = "pallas";
constant "Encrypt" {}
witness "Encrypt" {
# We are encrypting values to this public key
EcNiPoint pubkey,
# Emphemeral secret value
Base ephem_secret,
# Values we are encrypting
Base value_1,
Base value_2,
Base value_3,
}
circuit "Encrypt" {
################################################
# 1. Derive shared secret using DH
################################################
ephem_pub = ec_mul_var_base(ephem_secret, pubkey);
ephem_pub_x = ec_get_x(ephem_pub);
ephem_pub_y = ec_get_y(ephem_pub);
# Used by the receiver to also derive the same shared secret
constrain_instance(ephem_pub_x);
constrain_instance(ephem_pub_y);
shared_secret = poseidon_hash(ephem_pub_x, ephem_pub_y);
################################################
# 2. Derive blinding factors for witness values
################################################
N1 = witness_base(1);
N2 = witness_base(2);
N3 = witness_base(3);
blind_1 = poseidon_hash(shared_secret, N1);
blind_2 = poseidon_hash(shared_secret, N2);
blind_3 = poseidon_hash(shared_secret, N3);
################################################
# 3. Encrypt the values by applying blinds
################################################
# This could be add or mul
enc_value_1 = base_mul(value_1, blind_1);
enc_value_2 = base_mul(value_2, blind_2);
enc_value_3 = base_mul(value_3, blind_3);
constrain_instance(enc_value_1);
constrain_instance(enc_value_2);
constrain_instance(enc_value_3);
}