darkfi/proofs/sapling3.prf

# You will need this repo:
# https://github.com/zcash/librustzcash/
# Then compare this code to the file:
# librustzcash/zcash_proofs/src/circuit/sapling.rs

# What is the LC stuff?
# Difference between AllocatedNum and Num
# Why BlsScalar vs JJScalar?
const:
    G_VCV: Point
    G_VCR: Point
    G_SPEND: Point
    G_PROOF: Point
    G_NOTE_COMMIT_R: Point
    G_NULL: Point

    CRH_IVK: Blake2sPersonalization
    NOTE_COMMIT: PedersenPersonalization
    MERKLE: list<PedersenPersonalization>
    PRF_NF: Blake2sPersonalization

def value_commit(value: U64, randomness: Scalar) -> Binary:
    let value_bits: Binary = value as Binary
    let value: Point = value * G_VCV

    let rcv: Binary = randomness as Binary
    let rcv: Point = rcv * G_VCR

    let cv: Point = value + rcv
    emit cv
    return value_bits

# The parameters to this function are the same as in:
#   struct Spend
contract input_burn(
    value: U64,                 # ValueCommitment.value
    randomness: Scalar,         # ValueCommitment.randomness

    ak: Point,                  # from ProofGenerationKey
    ar: Scalar,

    nsk: Scalar,                # from ProofGenerationKey

    g_d: Point,                 # Computed from payment_address

    commitment_randomness: Scalar,

    auth_path: list<(Scalar, Bool)>,

    anchor: Scalar
) -> (Point, Point, Point, Binary):
    let ak = witness(ak)
    ak.assert_not_small_order()

    let ar: Binary = ar as Binary
    let ar: Point = ar * G_SPEND

    let rk: Point = ak + ar

    let nsk: Binary = nsk as Binary
    let nk: Point = nsk * G_PROOF

    let mut ivk_preimage: Binary = []
    # Must be Binary as well
    ivk_preimage.extend(ak.repr())

    let mut nf_preimage: Binary = []
    let nk_repr: Binary = nk.repr()
    ivk_preimage.extend(nk_repr)
    nf_preimage.extend(nk_repr)

    assert len(ivk_preimage) == 512
    assert len(nf_preimage) == 256

    let mut ivk: Binary = blake2s(ivk_preimage, CRH_IVK)
    ivk.truncate(Scalar::CAPACITY)

    let g_d: Point = witness g_d
    g_d.assert_not_small_order()

    let pk_d: Point = ivk * g_d

    let mut note_contents: Binary = []

    let (cv: Point, value_bits: Binary) = value_commit(value, randomness)

    let mut value_num: Num = Num.zero()
    let mut coeff: Scalar = Scalar.one()
    for bit in value_bits:
        value_num = value_num.add_Bool_with_coeff(bit, coeff)
        coeff = coeff.double()
    # Is this equivalent?
    let value_num = value_bits as Num

    note_contents.extend(value_bits)
    note_contents.extend(g_d)
    note_contents.extend(pk_d)

    assert len(note_contents) == 64 + 256 + 256

    let mut cm: Point = pedersen_hash(NOTE_COMMIT, note_contents)
    let rcm: Binary = commitment_randomness as Binary
    let rcm: Point = rcm * G_NOTE_COMMIT_R
    cm += rcm

    let mut position_bits: Binary = []
    let mut cur: Scalar = cm.u

    # This should be fixed: for i in 0..N then use array indexing
    for i, (node, is_right) in enumerate(auth_path):
        position_bits.push(is_right)

        let node: EncryptedNum = EncryptedNum.from(node)
        print(node)
        let (left: Binary, right: Binary) = Num.swap_if(is_right, cur, node)

        let mut preimage: Binary = []
        preimage.extend(left)
        preimage.extend(right)

        cur = pedersen_hash(MERKLE_TREE[i], preimage).u

    let rt: Point = EncryptedNum.from(anchor)

    enforce (cur - rt) * value_num == 0

    let position: Point = position_bits * G_NULL
    let rho: Point = cm + position

    nf_preimage.extend(rho)
    assert len(nf_preimage) == 512
    let nf: Binary = blake2s(nf_preimage, PRF_NF)

    emit (rk, cv, rt, nf)

contract output_mint(
    value: U64,
    randomness: Scalar,

    g_d: Point,

    esk: Scalar,
    pk_d: Point,

    commitment_randomness: Scalar
) -> (Point, Point, Scalar):
    let (cv: Point, value_bits: Binary) = value_commit(value, randomness)

    let mut note_contents: Binary = []
    note_contents.extend(value_bits)

    let g_d: Point = witness g_d
    assert is_not_small_order(g_d)

    let esk: Binary = esk as Binary
    let epk: Point = esk * g_d

    let v_contents: Binary = pk_d.v as Binary

    let sign_bit: Bool = pk_d.u.is_odd() as Bool

    note_contents.extend(v_contents)
    note_contents.push(sign_bit)

    assert len(note_contents) == 64 + 256 + 256

    let mut cm: Point = pedersen_hash(NOTE_COMMIT, note_contents)

    let rcm: Binary = commitment_randomness as Binary
    let rcm: Point = rcm * G_NOTE_COMMIT_R

    cm += rcm

    let cmu: Scalar = cm.u

    emit (cv, epk, cmu)