deoxysii async primitive

crypto/deoxysii.js

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+const nacl = require('tweetnacl');
+const deoxys = require('deoxysii');
+
+const boxKDFTweak_str = 'MRAE_Box_Deoxys-II-256-128';
+var boxKDFTweak = Buffer.alloc(boxKDFTweak_str.length);
+for (var i = 0; i < boxKDFTweak_str.length; i++) {
+  boxKDFTweak[i] = boxKDFTweak_str.charCodeAt(i);
+}
+
+// ECDHAndTweak applies the X25519 scalar multiply with the given public and
+// private keys, and applies a HMAC based tweak to the resulting output.
+function ECDHAndTweak(PublicKey, PrivateKey) {
+    let PreMasterKey = nacl.scalarMult(PrivateKey, PublicKey);
+
+    let hash = require('crypto').createHmac('sha256', boxKDFTweak);
+    hash.update(PreMasterKey);
+    return new Uint8Array(hash.digest());
+}
+
+module.exports = {
+  Seal: async function(Nonce, Plaintext, AdditionalData, PeerPublicKey, PrivateKey) {
+    let AesKey = ECDHAndTweak(PeerPublicKey, PrivateKey);
+
+    let AEAD = new deoxys.AEAD(AesKey);
+    return AEAD.encrypt(Nonce, Plaintext, AdditionalData);
+  },
+
+  Open: async function(Nonce, Ciphertext, AdditionalData, PeerPublicKey, PrivateKey) {
+    let AesKey = ECDHAndTweak(PeerPublicKey, PrivateKey);
+
+    let AEAD = new deoxys.AEAD(AesKey);
+    return AEAD.decrypt(Nonce, Ciphertext, AdditionalData);
+  }
+};