qaci-crypto

This module implements abstractions over cryptographic functions which MACI employs.

Constants

NOTHING_UP_MY_SLEEVE: The Keccack256 hash of the string "Maci", modulo the BN254 group order.

Types and interfaces

PrivKey: A private key (a random value modulo the BN254 group order).

PubKey: An EdDSA public key.

Keypair: A private key and the public key it generates.

EcdhSharedKey: An Elliptic-curve Diffie–Hellman shared key.

Plaintext: An array of unencrypted values.

Ciphertext: Encrypted Plaintext. This data structure abstracts over the initialisation vector and encrypted data.

Signature: A signature. This data structure abstracts over theR8 and S values.

Classes

G1Point: A point in the group G_1 as defined in EIP-197.

G2Point: A point in the group G_2 as defined in EIP-197.

Functions

genRandomBabyJubValue: Returns a cryptographically secure random value modulo the BN254 group order, and prevents modulo bias. Relies on Node.js's crypto.randomBytes(32) for entropy.

genRandomSalt: BigInt

Returns a secure random salt value. Wraps genRandomBabyJubValue().

genPrivKey: PrivKey

Returns a secure random private key. Wraps genRandomBabyJubValue().

genPubKey = (privKey: PrivKey): PubKey

Generates the public key associated with the given private key.

genKeypair: Generates a random private key and its associated public key.

formatPrivKeyForBabyJub = (privKey: PrivKey): Formats a random private key to be compatible with the BabyJub curve. This is the format which should be passed into the PubKey and other circuits.

packPubKey = (pubKey: PubKey): Buffer: Losslessly reduces the size of the representation of a public key.

unpackPubKey = (packed: Buffer): PubKey: Restores the original PubKey from its packed representation.

genEcdhSharedKey = (privKey: PrivKey, pubKey: PubKey): EcdhSharedKey

Generates an ECDH shared key.

encrypt = (plaintext: Plaintext, sharedKey: EcdhSharedKey): Ciphertext

Encrypts the plaintext with the given key and returns the associated ciphertext.

decrypt = (ciphertext: Ciphertext, sharedKey: EcdhSharedKey): Plaintext

Decrypts the ciphertext using the given key.

sign = (privKey: PrivKey, message: Plaintext): Signature

Produces a signature of the given message using the private key.

verifySignature = (message: Plaintext, signature: Signature, publicKey: PubKey): boolean

Checks whether the given signature is valid.

Hash functions

sha256Hash = (input: BigInt[]): BigInt: a wrapper function over ethers.utils.soliditySha256, where the output is modulo the BN254 group order.

hashOne = (elements: Plaintext): BigInt: the Poseidon hash function for one input. Equivalent to hash2([input, 0]).

hash2 = (elements: Plaintext): BigInt: the Poseidon hash function for 2 inputs.

hashLeftRight = (left: BigInt, right: BigInt): BigInt: equivalent to hash2([left, right]).

hash3 = (elements: Plaintext): BigInt: the Poseidon hash function for 3 inputs.

hash4 = (elements: Plaintext): BigInt: the Poseidon hash function for 4 inputs.

hash5 = (elements: Plaintext): BigInt: the Poseidon hash function for 5 inputs.

hash12 = (elements: Plaintext): BigInt: the Poseidon hash function for 12 inputs. Combines other Poseidon hash functions (accepting 5 and 6 inputs) to do so. Given the following inputs [i_0, i_1, ... i_11], this function hashes them in the following manner:

hash4(
    hash5([i_0, i_1, i_2, i_3, i_4]),
    hash5([i_5, i_6, i_7, i_8, i_9]),
    i_10,
    i_11,
)