Prepare Private Inputs

The gcEVM handles private inputs by encapsulating them within an Inputtext object. To utilize a private input, one must construct an Inputtext instance using their input data.

Each Inputtext instance includes an encrypted representation of the amount and a signature generated by concatenating the sender's address, contract address, function, and the encrypted amount.

The SDK offers a function designed to facilitate the creation of Inputtext objects from the specified data.

The function signature is provided in Python, JavaScript, and Go languages as follows:

Python

def prepare_IT(plaintext, user_aes_key, sender, contract, func_sig, signing_key)

Typescript

function prepareIT(plaintext, userAesKey, sender, contract, hashFunc, signingKey)

The function encrypts the plaintext using the AES key to get the ciphertext, then sign the concatenation of the addresses, hashed function signature and ciphertext using the ECDSA private key.

Input parameters:

• plaintext to encrypt

• AES key

• sender address

• contract address

• function signature (as string in go and python case, or hashed in js case)

• ECDSA private key.

Output:

• Ciphertext

• Signature

Example usage - Private ERC20

When conducting a private amount transfer, the value needs to be converted into an Inputtext format. Below are examples demonstrating how to utilize the prepare IT function in both Python and JavaScript languages:

Python

# In order to generate the input text, we need to use some data of the function. 
# For example, the address of the user, the address of the contract and also the function signature.
# To simplify the process of obtaining the function signature, we use a dummy function with placeholder inputs.
# After the signature is generated, we call prepare input text function and get the input text to use in the real function.
dummyCT = 0
dummySignature = bytes(65)
function = contract.functions.transfer(alice_address.address, dummyCT, dummySignature, False)
func_sig = get_function_signature(function.abi) # Get the function signature
# Prepare the input text for the function
ct, signature = prepare_IT(plaintext_integer, user_key, account, contract, func_sig, bytes.fromhex(private_key[2:]))
# Create the real function using the prepared IT
function = contract.functions.transfer(alice_address.address, ct, signature, False)

Typescript

// In order to generate the input text, we need to use some data of the function. 
// For example, the address of the user, the address of the contract and also the function signature.
// To simplify the process of obtaining the function signature, we use a dummy function with placeholder inputs.
// After the signature is generated, we call prepare input text function and get the input text to use in the real function.
const dummyCT = 0;
const dummySignature = Buffer.alloc(65);
func = contract.methods.transfer(alice_address.address, dummyCT, dummySignature, false); // Create dummy function to get the signature for prepare input text
let hashFuncSig = getFunctionSignature(func);
// After the function signature is obtained, prepare the input test for the function
let {ctInt, signature} = prepareIT(plaintext_integer, user_key, account.address, contract.options.address, hashFuncSig, Buffer.from(SIGNING_KEY.slice(2), 'hex'));
// Create the real function using the prepared IT
func = contract.methods.transfer(alice_address.address, ctInt, signature, false);