PineNaCl
PineNaCl is a Dart implementation of the TweetNaCl
the world's first auditable highsecurity cryptographic library.
This dart implementation based on the tweetnacldart
library, but it's slightly rewritten and extended by some higher level API implementations, similar to the PyNaCl library's APIs and concepts, for reallife
applications.
Thes library has the aim of
 improving the
 usability, by implementing highlevel and simpletouse APIs,
 security and speed, by using the dart implementation of the highsecurity
TweetNaCl
library.
 and providing a simple API for creating reallife applications easier.
Installing
 Add the following into the
pubspec.yaml
of your dart package:
dependencies:
pinenacl: ^0.6.0
 You can install now from the command line with pub:
$ pub get
 In your
Dart
code, you can use the similar:
import 'package:pinenacl/api.dart';
import 'package:pinenacl/public.dart';
Features
PineNaCl
reuses a lot of terminologies, concepts, sections of documents and implements examples and some features from, the before mentioned PyNaCl's publicly available readthedocs.io.
Implemented features:
 ECDH (with Curve25519) for key exchange (authenticated encryptions)
 Publickey Encryption
 Box (publickey authenticated encryption) and
 SealedBox
 Privatekey encryption
 SecretBox (privatekey authenticated encryption)
 Publickey Encryption
 EdDSA for Digital signatures (signing). It is complete (they are valid for all points on the curve) and deterministic i.e. no unique random nonce is required.
 Ed25519 Signatures i.e. Curve25519 with SHA512.
 Hashing and message authentication
 SHA256,
 SHA512, the default hashing algorithm of the original
TweetNaCl
 BLAKE2b for KDF and MAC (not implemented in
TweetNaCl
).  HMACSHA512.
 Password based key derivation and password hashing.
 PBKDF2 with
HMACSHA512
, iterating theHMACSHA512
many times on a combination of the password and a random salt.
 PBKDF2 with
Lowlevel Functions supported by PineNaCl
This library supports all 25 of the C NaCl functions, that can be used to build NaCl
applications.
 crypto_box = crypto_box_curve25519xsalsa20poly1305
 crypto_box_open
 crypto_box_keypair
 crypto_box_beforenm
 crypto_box_afternm
 crypto_box_open_afternm
 crypto_core_salsa20
 crypto_core_hsalsa20
 crypto_hashblocks = crypto_hashblocks_sha512
 crypto_hash = crypto_hash_sha512
 crypto_onetimeauth = crypto_onetimeauth_poly1305
 crypto_onetimeauth_verify
 crypto_scalarmult = crypto_scalarmult_curve25519
 crypto_scalarmult_base
 crypto_secretbox = crypto_secretbox_xsalsa20poly1305
 crypto_secretbox_open
 crypto_sign = crypto_sign_ed25519
 crypto_sign_keypair
 crypto_sign_open
 crypto_stream = crypto_stream_xsalsa20
 crypto_stream_salsa20
 crypto_stream_salsa20_xor
 crypto_stream_xor
 crypto_verify_16
 crypto_verify_32
However a simple NaCl
application would only need the following six highlevel NaCl API functions.
 crypto_box for publickey authenticated encryption;
 crypto_box_open for verification and decryption;
 crypto_box_keypair to create a public key (scalarmult k with basepoint B=9) for key exchange.
Similarly for signatures
 crypto_sign,
 crypto_sign_open, and
 crypto_sign_keypair, to create signing keypair for signing (scalarmult k with basepoint B=(x, 4/5))
Extension to the TweetNaCl
The following NaCl
library's highlevel functions are implemented as the extension to the TweetNaCl
library.
 HMACSHA512 and HMACSHA256
 crypto_auth = crypto_auth_hmacsha512, HMACSHA512
 crypto_auth_hmacsha256, HMACSHA256
 Hashing algorithm
 crypto_hash_sha256, SHA256
 Utils
 crypto_verify_64, verifying function for SHA512 as an example
 X25519 conversion utilities
 crypto_sign_ed25519_sk_to_x25519_sk
 crypto_sign_ed25519_pk_to_x25519_pk
 Curve25519 lowlevel functions
 crypto_scalar_base, for retrieving different type of publickeys e.g.
A = k * B
.  crypto_point_add, for adding two public keys' point together
A = y1 : y2
.
 crypto_scalar_base, for retrieving different type of publickeys e.g.
Key Types
Key id*  Alt key id  Key length  Function  Comment 

ed25519_sk  ed25519_skpk  64  Digital Signatures (EdDSA)  Ed25519 signing key. It can be converted to X25519 secret key for authenticated encryption. 
ed25519_pk  32  Digital Signatures (EdDSA)  Ed25519 verifying key. It can be converted to X25519 public key for authenticated encryption 

x25519_sk  curve25519_sk  32  Authenticated encryption (ECDH)  X25519 private key. 
x25519_pk  curve25519_pk  32  Authenticated encryption (ECDH)  X25519 public key. 
ed25519e_sk  ed25519_esk  64  EdDSA and ECDH  The first 32 byte is a valid X25519 secret key. 
ed25519_pk  ed25519e_pk  32  EdDSA  It's an Ed25519 verifying key, so it can be converted to X25519 public key. 
*: Key id is the HumanReadable Part (HRP) of the Bech32 (binarytotext encoding standard/scheme) encoded keys used in pinenacldart
.
Examples
PineNaCl
comes /w the following examples:
Public Key Encryption
examples Box example and its source code.
 SealedBox example and its source code.
Private Key Encryption
example SecretBox example and its source code.
Digital Signatures
example Signatures example and its source code.
Hashing
example Hashing example and its source code.
Public Key Encryption
example
Implemented from PyNaCl's example
Box
Imagine Alice wants something valuable shipped to her. Because it’s valuable, she wants to make sure it arrives securely (i.e. hasn’t been opened or tampered with) and that it’s not a forgery (i.e. it’s actually from the sender she’s expecting it to be from and nobody’s pulling the old switcheroo).
One way she can do this is by providing the sender (let’s call him Bob) with a highsecurity box of her choosing. She provides Bob with this box, and something else: a padlock, but a padlock without a key. Alice is keeping that key all to herself. Bob can put items in the box then put the padlock onto it. But once the padlock snaps shut, the box cannot be opened by anyone who doesn’t have Alice’s private key.
Here’s the twist though: Bob also puts a padlock onto the box. This padlock uses a key Bob has published to the world, such that if you have one of Bob’s keys, you know a box came from him because Bob’s keys will open Bob’s padlocks (let’s imagine a world where padlocks cannot be forged even if you know the key). Bob then sends the box to Alice.
In order for Alice to open the box, she needs two keys: her private key that opens her own padlock, and Bob’s wellknown key. If Bob’s key doesn’t open the second padlock, then Alice knows that this is not the box she was expecting from Bob, it’s a forgery.
This bidirectional guarantee around identity is known as mutual authentication.
 PyNaCl
import 'package:pinenacl/api.dart';
import 'package:pinenacl/public.dart' show PrivateKey;
void main() {
// Generate Bob's private key, which must be kept secret
final skbob = PrivateKey.generate();
// Bob's public key can be given to anyone wishing to send
// Bob an encrypted message
final pkbob = skbob.publicKey;
// Alice does the same and then Alice and Bob exchange public keys
final skalice = PrivateKey.generate();
final pkalice = skalice.publicKey;
// Bob wishes to send Alice an encrypted message so Bob must make a Box with
// his private key and Alice's public key
final bobBox = Box(myPrivateKey: skbob, theirPublicKey: pkalice);
// This is our message to send, it must be a bytestring as Box will treat it
// as just a binary blob of data.
final message = 'There is no conspiracy out there, but lack of the incentives to drive the people towards the answers.';
// TweetNaCl can automatically generate a random nonce for us, making the encryption very simple:
// Encrypt our message, it will be exactly 40 bytes longer than the
// original message as it stores authentication information and the
// nonce alongside it.
final encrypted = bobBox.encrypt(message.codeUnits);
// Finally, the message is decrypted (regardless of how the nonce was generated):
// Alice creates a second box with her private key to decrypt the message
final aliceBox = Box(myPrivateKey: skalice, theirPublicKey: pkbob);
// Decrypt our message, an exception will be raised if the encryption was
// tampered with or there was otherwise an error.
final decrypted = aliceBox.decrypt(encrypted);
print(String.fromCharCodes(decrypted.plaintext));
}
SealedBox
The SealedBox class encrypts messages addressed to a specified keypair by using ephemeral sender’s keypairs, which will be discarded just after encrypting a single plaintext message.
This kind of construction allows sending messages, which only the recipient can decrypt without providing any kind of cryptographic proof of sender’s authorship.
Warning
By design, the recipient will have no means to trace the ciphertext to a known author, since the sending keypair itself is not bound to any sender’s identity, and the sender herself will not be able to decrypt the ciphertext she just created, since the private part of the key cannot be recovered after use.
 PyNaCl
import 'package:pinenacl/public.dart' show SealedBox, PrivateKey;
void main() {
// Generate Bob's private key, which must be kept secret
final skbob = PrivateKey.generate();
final pkbob = skbob.publicKey;
// Alice wishes to send a encrypted message to Bob,
// but prefers the message to be untraceable
// she puts it into a secretbox and seals it.
final sealedBox = SealedBox(pkbob);
final message = 'The world is changing around us and we can either get '
'with the change or we can try to resist it';
final encrypted = sealedBox.encrypt(message.codeUnits);
// Bob unseals the box with his privatekey, and decrypts it.
final unsealedBox = SealedBox(skbob);
final plainText = unsealedBox.decrypt(encrypted);
print(String.fromCharCodes(plainText));
assert(message == String.fromCharCodes(plainText));
}
A Secret Key Encryption
example
Implemented from PyNaCl's example
SecretBox
Secret key encryption (also called symmetric key encryption) is analogous to a safe. You can store something secret through it and anyone who has the key can open it and view the contents. SecretBox functions as just such a safe, and like any good safe any attempts to tamper with the contents are easily detected.
Secret key encryption allows you to store or transmit data over insecure channels without leaking the contents of that message, nor anything about it other than the length.
 PyNaCl
import 'package:pinenacl/api.dart';
import 'package:pinenacl/secret.dart' show SecretBox;
void main() {
final key = Utils.randombytes(SecretBox.keyLength);
final box = SecretBox(key);
final message = 'Change is a tricky thing, it threatens what we find familiar with...';
final encrypted = box.encrypt(message.codeUnits);
final decrypted = box.decrypt(encrypted);
final ctext = encrypted.ciphertext;
assert(ctext.length == message.length + SecretBox.macBytes);
final plaintext = String.fromCharCodes(decrypted.plaintext);
print(plaintext);
assert(message == plaintext);
}
Digital Signatures
example
Implemented from PyNaCl's example
Signing
You can use a digital signature for many of the same reasons that you might sign a paper document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender such that they cannot deny sending it (authentication and nonrepudiation) and that the message was not altered in transit (integrity).
Digital signatures allow you to publish a public key, and then you can use your private signing key to sign messages. Others who have your public key can then use it to validate that your messages are actually authentic.
 PyNaCl
import 'package:convert/convert.dart';
import 'package:pinenacl/signing.dart';
void main() {
///
/// Signer’s perspective (SigningKey)
///
// Generate a new random signing key
final signingKey = SigningKey.generate();
final message = 'People see the things they want to see...';
// Sign a message with the signing key
final signed = signingKey.sign(message.codeUnits);
// Obtain the verify key for a given signing key
final verifyKey = signingKey.verifyKey;
// Serialize the verify key to send it to a third party
final verifyKeyHex = hex.encode(verifyKey);
///
/// Verifier’s perspective (VerifyKey)
///
final verifyKey2 = VerifyKey.fromHexString(verifyKeyHex);
assert(verifyKey == verifyKey2);
print('The "$message" is successfully verified');
// Check the validity of a message's signature
// The message and the signature can either be passed separately or
// concatenated together. These are equivalent:
verifyKey.verify(signed);
verifyKey.verify(signed.message, signed.signature);
// Alter the signed message text
signed[0] ^= signed[0] + 1;
try {
// Forged message.
verifyKey.verify(signed);
} on Exception catch(e) {
print('Successfully cought: $e');
}
}
Hashing
example
Implemented from PyNaCl's example
Cryptographic secure hash functions are irreversible transforms of input data to a fixed length digest.
The standard properties of a cryptographic hash make these functions useful both for standalone usage as data integrity checkers, as well as
blackbox
building blocks of other kind of algorithms and data structures.All of the hash functions exposed in
hashing
can be used as data integrity checkers.As already hinted above, traditional cryptographic hash functions can be used as building blocks for other uses, typically combining a secretkey with the message via some construct like the HMAC one.
 PyNaCl
Blake2b
The
blake2b
hash function can be used directly both formessage authentication
andkey derivation
, replacing the HMAC construct and the HKDF one by setting the additional parameterskey
,salt
andperson
.
Warning
Please note that key stretching procedures like
HKDF
or the one outlined inKey derivation
are not suited to derive acryptographicallystrong key
from alowentropy input
like aplaintext password
or to compute a strong longterm stored hash used as password verifier. PyNaCl
Hashing
...
void main() {
final hasher = Hash.blake2b;
print('Hash example\nH(\'\'): ${hex.encode(hasher(''))}');
Message authentication
To authenticate a message, using a secret key, the blake2b function must be called as in the following example.
/// It can ganarate a MAC to be sure that the message is not forged.
final msg = '256 BytesMessage' * 16;
// the simplest way to get a cryptographic quality authKey
// is to generate it with a cryptographic quality
// random number generator
final authKey = Utils.randombytes(64);
final mac = hasher(msg, key: authKey);
print('MAC(msg, authKey): ${hex.encode(mac)}.\n');
Key derivation
The blake2b algorithm can replace a key derivation function by following the lines of:
print('Key derivation example');
final masterKey = Utils.randombytes(64);
final derivationSalt = Utils.randombytes(16);
final personalisation = Uint8List.fromList('<DK usage>'.codeUnits);
final subKey = hasher('', key: masterKey, salt: derivationSalt, personalisation: personalisation);
print('KDF(\'\', masterKey, salt, personalisation): ${hex.encode(subKey)}');
By repeating the key derivation procedure before encrypting our messages, and sending the derivationSalt along with the encrypted message, we can expect to never reuse a key, drastically reducing the risks which ensue from such a reuse.
TODOS
x
Implement encoding/decoding) classes.x
Add more unit tests.x
Refactor to much simpler code.x
Simplify or refactor the APIs and modules' dependencies.x
Removebech32
,hex
andconvert
pakages dependency.x
Removefixnum
pakage dependency.x
Add Ed25519 to X25519 function, to allow Ed25519 to be used in authenticated encryption too, see note below.x
Refactor key derivation function to be able to use diffhmac
s.x
OptimiseSHA256
for faster execution. Done 5 time faster now 0.41 sec instead of 3.1 sec for 256K iterations.SHA512
for faster execution.x
Add some benchmark files.
Note: Ed25519
keys that are used only for digital signatures (EdDSA), can be
converted to Curve25519/X25519
key (that is used only for authenticated encryption i.e.
ECDH), therefore the same key pairs can be used for
 digital signatures (EdDSA), as it's already used, using
crypto_sign
and  authenticated encryption (ECDH) using
crypto_box
.
Thanks and Credits
 PyNaCl library
 TweetNaCl dart implementation
 TweetNaCl: a crypto library in 100 tweets
 blake2b
 bech32
 And many others...
References
 How do Ed5519 keys work?
 Using Ed25519 signing keys for authenticated encryption
 The Provable Security of Ed25519: Theory and Practice
 Implementing Curve25519/X25519: A Tutorial on Elliptic Curve Cryptography