src/ecc/aes.js
function decrypt(private_key, public_key, nonce, message, checksum) {
    return crypt(private_key, public_key, nonce, message, checksum).message;
}
function decrypt(private_key, public_key, nonce, message, checksum) {
    return crypt(private_key, public_key, nonce, message, checksum).message;
}
Spec: http://localhost:3002/steem/@dantheman/how-to-encrypt-a-memo-when-transferring-steem

@arg {PrivateKey} private_key - required and used for decryption
@arg {PublicKey} public_key - required and used to calcualte the shared secret
@arg {string} nonce - random or unique uint64, provides entropy when re-using the same private/public keys.
@arg {Buffer} message - Encrypted or plain text message
@arg {number} checksum - shared secret checksum

@throws {Error|TypeError} - "Invalid Key, ..."

@return {Buffer} - message